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IAC Valve?

 
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Arnold
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PostPosted: Fri, May 22 2015, 11:14 am    Post subject: IAC Valve? Reply with quote

I really know nothing about these. I read a bit and seems to me..they are hard to test properly..and are a cheap throw a part at it thing and see Laughing
I took mine out and it was in the fully open position..and could not move it. I read that some of them you cannot move and if you do move it you broke it..or was broke. I read sometimes they stick and become junk.Open or closed.
First price I got was $80.Cdn..here in Canada. Seems like I should wait for RockAuto or the like for like $15 haha.

Symptoms. Is this an iac problem?

1994 Chev 1 ton van. 5.7. tbi.

Starts ok..runs rough..not that responsive..will idle. Low power until it warms up.Once warm it runs much worse below about 1500rpm. Has absolute zero power just above an idle..will idle but will stall immediately even in neutral with any throttle
ncrease engine rpm is to first start it with full throttle..then back it off to about 1500..and use it from there and above.
I checked the spray pattern at idle and just above idle as soon as the throttle is opened.All is well there. Any throttle and it just dies.
Runs so badly right now when warm that I could not really drive it.
Sound like an iac? This always idles.
Thanks As Usual Laughing

Ya..this does not make me that happy as I go through my vehicle expense records and see that it cost the same to operate my old van for the last 7 years as it did my sub compact 4 cyl car. My basic insurance coverage for my car will now be almost 40% higher for the most very basic no collision insurance thanthe van.

I just want to get my van running nice before I send it to it's scrap yard burial. Not gonna spend much..maybe zero money on this.

Might even buy another big chev van..used..with awd.
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kb426
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PostPosted: Fri, May 22 2015, 12:19 pm    Post subject: Reply with quote

All the iacs I have worked on are driven by stepper motors. I can unscrew the plungers on most but can't move them by pushing on them. My thought is that it isn't your iac but I believe you need to connect a code reader to see what's going on. You can always unplug the wiring connection on the iac to see if it's different. If the plunger is in the closed position when you do this, you will eliminate that source of vacuum-air from entering the engine.
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PostPosted: Fri, May 22 2015, 1:19 pm    Post subject: Reply with quote

kb426 wrote:
All the iacs I have worked on are driven by stepper motors. I can unscrew the plungers on most but can't move them by pushing on them. My thought is that it isn't your iac but I believe you need to connect a code reader to see what's going on. You can always unplug the wiring connection on the iac to see if it's different. If the plunger is in the closed position when you do this, you will eliminate that source of vacuum-air from entering the engine.


Thanks Very Happy There are of course no codes Laughing This is an OBD 1..or 1 1/2.
I don't have a reader that will read this live..or even show values. I think there is some way of doing this by accessing the terminals..I dunno.
I know it works because when the egr went it showed that/fixed that/light out. I did manage to check it for codes too and it didn't show any.
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PostPosted: Fri, May 22 2015, 2:08 pm    Post subject: Reply with quote

Would this be of help?
http://www.troublecodes.net/GM/

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PostPosted: Fri, May 22 2015, 3:18 pm    Post subject: Reply with quote

kb426 wrote:
Would this be of help?
http://www.troublecodes.net/GM/


Thanks again..the cel is not on..it did come on before and I accessed the terminals and it showed an egr. I changed that/light out/no light/no codes. Now it still shows no codes. I can't believe anything can run this bad and not show cel/codes. Maybe a bad comp.? I dunno. I thought there was a way of accessing problems live with these old systems by jumping..maybe not. I am pretty sure there are some newer scanners that will do these old things live.
Even though it idles I am thinking iac.
Maybe I just rig something up to set the idle about 1500 then it would be ok. Laughing
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UGLY OLDS
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PostPosted: Fri, May 22 2015, 6:44 pm    Post subject: Reply with quote

Arnold ...
Try this ....

First verify that the EGR valve you replaced is working properly .. The symptoms you are providing sound just like a sticking / hung up EGR valve ..
Here is the procedure to re-set the IAC motor .....
Install the IAC motor in the throttle body...

Remove the "ECM B" fuse for about 30 seconds to clear memory. Reconnect. Jump the A&B terminals like you're going to check codes. Turn key on, wait about 30 seconds. Turn key off. Remove jumper from A&B terminals. Done.

What this does is close the IAC and set the ECM's memory for its position at full closed. It's a "dumb" system with no feedback, so the ECM can only work off an assumed position of the IAC and send it commands to open or close as it sees fit. This requires a known baseline setting, provided by the reset.

I have also seen the IAC passage gum up with varnish & gunk ... It is a square opening at the R/Rear part of the throttle body directly above the IAC motor just inside where the Air Cleaner ring sets ...
These engines were also notorious for having the T/Body base gasket go bad & cause a vacuum leak ...

Hope this helps resolve the issue ...

Bob..... Wink

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Arnold
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PostPosted: Sat, May 23 2015, 10:26 am    Post subject: Reply with quote

UGLY OLDS wrote:
Arnold ...
Try this ....

First verify that the EGR valve you replaced is working properly .. The symptoms you are providing sound just like a sticking / hung up EGR valve ..
Here is the procedure to re-set the IAC motor .....
Install the IAC motor in the throttle body...

Remove the "ECM B" fuse for about 30 seconds to clear memory. Reconnect. Jump the A&B terminals like you're going to check codes. Turn key on, wait about 30 seconds. Turn key off. Remove jumper from A&B terminals. Done.

What this does is close the IAC and set the ECM's memory for its position at full closed. It's a "dumb" system with no feedback, so the ECM can only work off an assumed position of the IAC and send it commands to open or close as it sees fit. This requires a known baseline setting, provided by the reset.

I have also seen the IAC passage gum up with varnish & gunk ... It is a square opening at the R/Rear part of the throttle body directly above the IAC motor just inside where the Air Cleaner ring sets ...
These engines were also notorious for having the T/Body base gasket go bad & cause a vacuum leak ...

Hope this helps resolve the issue ...

Bob..... Wink


That is some really great info Exclamation Thanks Very Happy
I also read somewhere that this system on this truck..iirc 1993-1996
G30 Vans 5.7 engines required a road speed of a minimum 38 mph at normal temperature and under normal driving conditions before it would allow the iac to re-set.
I sprayed all around looking for vac leaks..unplugged all the vacuum stuff. I sprayed Sea Foam..then starting fluid.. nothing made any difference.
I am tempted to also think that there is some crap in there somewhere.I might put some of that GM stuff in.
Sad to see this old truck reduced to this.
This is still a seriously powerful truck from 1500 rpm and up.
Yes..my old 1994 1 ton 5.7 Van had like 10 times the low end power of mine and my GF's 6.0's. Makes my 6.0 HO Police engine seem just inadequate at low rpm Laughing

I have felt/tested the egr/vac.W w/o..this thing idles but just DIES
at ANY throttle..get at going from a full throttle crank and let it back down to about 1500..ya..I can't see anything wrong there. I need to move this truck haha. This is not a vehicle that one should move at a screaming idle.

I don't think it can be plugged up that bad..I had the iac out..ran Sea Foam through it..plugs are new..fires well..new cap/rotor. Doesn't seem to make much difference.

Think I'll try either a used or cheap iac next. I think mine is stuck open.

Thanks Very Happy
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PostPosted: Sat, May 23 2015, 3:07 pm    Post subject: Reply with quote

Have you thought of blocking the iac port off as a diagnostic tool? A lot of what you describe makes me think you could a weak spark or a fuel pressure problem. I think those older systems are 14-16 lbs. It wouldn't take much to cause an off throttle problem. At idle does it sound correct?
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PostPosted: Mon, May 25 2015, 9:35 am    Post subject: Reply with quote

kb426 wrote:
Have you thought of blocking the iac port off as a diagnostic tool? A lot of what you describe makes me think you could a weak spark or a fuel pressure problem. I think those older systems are 14-16 lbs. It wouldn't take much to cause an off throttle problem. At idle does it sound correct?


Thanks..for your continued help Very Happy I haven't had time to look at it in the last few days..
I have thought about just getting an iac and stuffing it in..or getting this one to it's extended..closed position and leaving it that way to test it.
Weak spark I don't think so..it runs too well from 1500 and above..plus I have tested the spark output sort of..by pulling off the leads and using an hei spark tester.both cranking and running.Seems ok.
Pump pressure..I have not tested it..but I doubt it..runs too well above 1500 and at idle..it sounds pretty good actually.It will idle pretty much forever.
An iac was like $80 Cdn locally..forget that..unless I know that is what it is. I am going to play around and try and test the iac..and the wiring to it next.

Thanks again
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PostPosted: Mon, May 25 2015, 9:42 am    Post subject: Reply with quote

Have you checked the tps to see if the output is linear? If it had a bad spot you could have no fuel delivery until it hit a spot where the voltage output caught up.
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PostPosted: Mon, May 25 2015, 10:12 am    Post subject: Reply with quote

kb426 wrote:
Have you checked the tps to see if the output is linear? If it had a bad spot you could have no fuel delivery until it hit a spot where the voltage output caught up.


I thought of that/checked that.Thanks.(It has fuel delivery..good spray..and then additional spray when you open the throttle..then it dies)
Doesn't even show anything bad during a vacuum test. Idle vac is a tad low at about 16 but seems to be ok otherwise.
Probably something stupid like some weak valve springs..allowing some valves to get yanked off their seats at high vacuum..big gulp of air..gasp..dies. Laughing
I also read that the coolant temp sensor on these things can wreak havoc too.
Might be a map too?
My feeling right now is to get it to the local garage that does a lot of my work..they work on lots of old stuff. They would find it then I would know and be happy and could send it to the scrap yard Laughing
I don't need it right now..but it sure bugs me as to what is wrong with it

Thanks again.. Very Happy
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PostPosted: Tue, May 26 2015, 5:27 pm    Post subject: Reply with quote

Arnold wrote:
kb426 wrote:
Have you checked the tps to see if the output is linear? If it had a bad spot you could have no fuel delivery until it hit a spot where the voltage output caught up.


I thought of that/checked that.Thanks.(It has fuel delivery..good spray..and then additional spray when you open the throttle..then it dies)
Doesn't even show anything bad during a vacuum test. Idle vac is a tad low at about 16 but seems to be ok otherwise.
Probably something stupid like some weak valve springs..allowing some valves to get yanked off their seats at high vacuum..big gulp of air..gasp..dies. Laughing
I also read that the coolant temp sensor on these things can wreak havoc too.
Might be a map too?
My feeling right now is to get it to the local garage that does a lot of my work..they work on lots of old stuff. They would find it then I would know and be happy and could send it to the scrap yard Laughing
I don't need it right now..but it sure bugs me as to what is wrong with it

Thanks again.. Very Happy


Un-plugged the iac while idling.Revving it up. No difference. No cel.Tried shuttijg it off disconnected..looking at it's position..it is still open. Probably stays open. Tried starting it with it connected,dis-connected.Clearly there is something wrong with the valve or the wiring to it or the comp.Or whatever else controls it. Might be as I mentioned I read need 38mph to re-set it.Tried Ugly Olds iac re-set.
Tried un-plugging the map..no difference there either.Cel came on as soon as I un-plugged it then off when I hooked it back up. Did not even store the code.

I read where someone had the same problem and it was the tank return fuel line. When it plugged up...the return fuel pressure added to the existing pump pressure now and again caused it to run rich.

Tried driving it. Not driveable. Just dies.
Tried some fresh gas and some cleaner.

Guess I will back probe the iac circuit and the comp.
Test the map..and back probe that circuit and back to the comp.
Coolant sensor. Can't find any way to test that. Wonder how much they are?
Fuel pressure test coming too..

Might head back to basics and do a comp test..on all the cyl. this time haha..watch it build pressure and then vac test back through the plug hole..with my finger..works every time Laughing Might see how much slop there is in the chain or dist.

I really don't want to junk it until I find out what is wrong with it Laughing

I still can't beiieve that it runs as it bad as it does and does not show any codes. LOL..doesn't even store a map code when I pull it off.
Code test just shows normal.

Thanks Guys Very Happy
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wayne petty
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PostPosted: Sun, May 31 2015, 5:35 am    Post subject: Reply with quote

idle issues. on GM trucks with TBI... engine off.. grab the throttle lever.. open it slightly.. wiggle.. it should move in and out only along the throttle shaft.. there should NOT be any or very little front to back play..

the linkage side gets a lot of wear.. because the throttle stop is against the lever.. the linkage can close to a slightly different position each time. this just freaks out the computer as it never knows when you really have your foot OFF the gas..

the screws are metric.. M2.5 x.45 i think.. custom large pan head..

i seem to recall you have access to a bunch of stuff.. got any engine rebuilders around.. they have if they do cylinder heads. K Line thin wall valve guide liners.. buy a few from them. get them for 0.375 or 0.376. most will have the 0.375 in stock.. measure the wall thickness.. 0.015. or 0.0145" for the 0.376. .. i know you can lay your hands on a Letter Y drill .0.404.

grind the damaged exposed threads off the throttle plate screws.. do not dig deep into the shaft with your grinder.. the last few threads are good close to the shaft.. you might want to back the screws out slightly till you feel them get snug but don't snap them off. then grind. this leave a little extra lenght to punch to lock them later.. with the throttle shaft out. you can drill the bore to 0.404.. use hose clamps on the thin wall liners on a 3/8 wooden dowel to cut to length with the dremel tool cut off disc.. insert.. if you have a .375 valve guide reamer.. you can go thru with that.. i usually go thru with my knurling finishing tool with WHITE GREASE so it does not get stuck.. i work the throttle shaft back in with grease also.. it is now nice and tight fitting.. you can reinstall the screws.. back off the idle stop screw so you can center the throttle plates in the bores.. adjust to the minimum throttle with the T15 screw just enough to prevent the throttle plates from sticking and going BOING when you open the throttle..

get the injectors bolted back in.. use G P Sorenson 800-9214 and 800-9215 for the fuel fitting orings.. autozones usually stock that number. i can cross it if you know what brands of seals your parts store carries.

i normally use a shop rag and a screw driver to pack the idle air passage closed to adjust minimum idle with the engine warmed up.

if you had access to a scan tool..

TPS at idle.. under 0.75.. above 0.35. but each time it must return to the EXACT SAME fraction of a volt. or it will confuse the computer.

looking at the idle air counts.. 20 to 50 at warmed up idle. is the best setting. adjusting the idle stop screw to reach it.. if its less than 20 .. close the throttle farther or check for vacuum leaks.. or oversized PCV valves. blown power brake booster.. if its more than 50.. open the throttle farther.. . coolant temp should be over 185 warmed up.. it should have a 192 F thermostat..

i change coils really often.. they leak externally.. fail a spark gap test.. must throw a bright blue snappy spark over 1/2 inch. if you only get a dim orange spark.. change the coil.

please print and perform the 6 step voltage drop test. http://i.imgur.com/WMDprhm.jpg why .. because i have had so many ground issues and power issues on these..

i found this online.. might help ..
http://forums.superchevy.com/corvette-fever/70/8585187/c4-corvettes/whi ch-used-scan-tools-for-82-to-94-corvettes-with/
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Arnold
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PostPosted: Mon, Jun 01 2015, 1:30 pm    Post subject: Reply with quote

wayne petty wrote:
idle issues. on GM trucks with TBI... engine off.. grab the throttle lever.. open it slightly.. wiggle.. it should move in and out only along the throttle shaft.. there should NOT be any or very little front to back play..

the linkage side gets a lot of wear.. because the throttle stop is against the lever.. the linkage can close to a slightly different position each time. this just freaks out the computer as it never knows when you really have your foot OFF the gas..

the screws are metric.. M2.5 x.45 i think.. custom large pan head..

i seem to recall you have access to a bunch of stuff.. got any engine rebuilders around.. they have if they do cylinder heads. K Line thin wall valve guide liners.. buy a few from them. get them for 0.375 or 0.376. most will have the 0.375 in stock.. measure the wall thickness.. 0.015. or 0.0145" for the 0.376. .. i know you can lay your hands on a Letter Y drill .0.404.

grind the damaged exposed threads off the throttle plate screws.. do not dig deep into the shaft with your grinder.. the last few threads are good close to the shaft.. you might want to back the screws out slightly till you feel them get snug but don't snap them off. then grind. this leave a little extra lenght to punch to lock them later.. with the throttle shaft out. you can drill the bore to 0.404.. use hose clamps on the thin wall liners on a 3/8 wooden dowel to cut to length with the dremel tool cut off disc.. insert.. if you have a .375 valve guide reamer.. you can go thru with that.. i usually go thru with my knurling finishing tool with WHITE GREASE so it does not get stuck.. i work the throttle shaft back in with grease also.. it is now nice and tight fitting.. you can reinstall the screws.. back off the idle stop screw so you can center the throttle plates in the bores.. adjust to the minimum throttle with the T15 screw just enough to prevent the throttle plates from sticking and going BOING when you open the throttle..

get the injectors bolted back in.. use G P Sorenson 800-9214 and 800-9215 for the fuel fitting orings.. autozones usually stock that number. i can cross it if you know what brands of seals your parts store carries.

i normally use a shop rag and a screw driver to pack the idle air passage closed to adjust minimum idle with the engine warmed up.

if you had access to a scan tool..

TPS at idle.. under 0.75.. above 0.35. but each time it must return to the EXACT SAME fraction of a volt. or it will confuse the computer.

looking at the idle air counts.. 20 to 50 at warmed up idle. is the best setting. adjusting the idle stop screw to reach it.. if its less than 20 .. close the throttle farther or check for vacuum leaks.. or oversized PCV valves. blown power brake booster.. if its more than 50.. open the throttle farther.. . coolant temp should be over 185 warmed up.. it should have a 192 F thermostat..

i change coils really often.. they leak externally.. fail a spark gap test.. must throw a bright blue snappy spark over 1/2 inch. if you only get a dim orange spark.. change the coil.

please print and perform the 6 step voltage drop test. http://i.imgur.com/WMDprhm.jpg why .. because i have had so many ground issues and power issues on these..

i found this online.. might help ..
http://forums.superchevy.com/corvette-fever/70/8585187/c4-corvettes/whi ch-used-scan-tools-for-82-to-94-corvettes-with/


Wayne..thanks as usual for a bunch of great info. Very Happy I do appreciate it.

I think this is toast..this engine. I think it is just too carbonned up..I did that when I really needed it a year or two ago. The egr came apart..rotted..it was gonna be like $175-$250 or something really stuped Canadian..then I dunno..from like Thursday until at least Tue to get it..so I backyarded a bracket up to hold the egr together. It ran too rich..I felt it..saw it..fuel mileage dropped..
I just kept driving it... Laughing until it quit Shocked

Thought I MIGHT drive it again Laughing but the black soot that kept blowing out...it would never get by emmssions. I kept thinking it was cleaned out..but then..there was more. Enough Sea Foam and GM F. I cleaner.

I took out the iac valve and cleaned it..and did that a few times..then it started to come to life..I never got that 100%..but it was a big improvement. Then I decided to re-visit the compression test. Do all of them this time Laughing One built pressure normally..but when I leaked it(at a few different spots) I could hear it hissing out just too bad..pretty sure it was a port leak..I am guessing that I just carbonned the thing up too bad and now..there was seat leakage. Could be that it was going anyway..I doubt that..these things go forever.
Anyway..I salvaged an old Chevette engine years ago. That one was junk from carbonned up. I actually had to pretty much seal the exhaust side of the engine..(so the cleaner would not run out Laughing )Filled it through the plug holes at bdc with valves open and managed to fiddle around and force the fluid up into the chambers..valve seat area..then filled the intake from the other end.Left that for a few days..cleaned it out..
I laughed so hard when I first pulled a plug out of that because it was so carbonned up there was pretty much no combustion chamber Laughing

That one re-turned to life and I drove it.

My old truck..I am not going to go that trouble..

I kept trying to clean it out last week by just revving it up..with cleaner in it..finally..it just got weaker and weaker..with my foot buried in it..missed worse..would not..could not idle..vac at as slow as it would barely run dropped to 8..
Won't start now. Just not enough cranking vaccum Crying or Very sad

I need to pull the heads. I told my g/f I would not spend time and money on this thing.

I might Twisted Evil
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PostPosted: Fri, Jun 05 2015, 1:06 am    Post subject: Reply with quote

the IDLE air control valve does NOTHING ABOVE idle.. other than act like a dash pot to prevent high manifold vacuum when you take your foot off the gas and close the throttle..

please verify the spark .. before you go anywhere else.. i have changed so many ignition coils on GM TBI and Vortec motors i cannot count them..

the sides of the coil will have marks like this grey area or worse on the sides
http://i.imgur.com/LIyPczv.jpg this is where the high voltage spark leaks out ..no high voltage spark.. you won't have enough voltage to flash over the spark plug and rotor to cap gap and the engine will misfire or die...

how long does it take to check for spark.. a minute... how long does it take to change a coil on a TBI or Vortec V8... under 15 minutes.. i did a vortec V6 coil in a 98 GMC safari in 12 minutes last week. but i already had the engine cover off so that is kinda cheating.

how to tell.. use a spark gap tester.. 8 bucks.. at most parts stores.. not the neon bulb type.. the adjustable gap type.. if your coil looks like above.. don't bother . just replace it.. you can pull the coil wire out of the cap.. position it 1/2" from something metal and crank then engine.. if you only get a dull orange spark.. replace.. if you get a SNAPPY BRIGHT BLUE spark... then the coil may be OK.

a few things that will make your truck also just die..

bad ground connections.. there is a computer to engine ground connection for the TPS and some of the other sensors on either the thermostat stud or the stud directly behind the thermostat. i have to replace that ring terminal the first time i work on so many TBI and Vortec engines another uncountable number..

but the Computer MAIN ground is to the back of the cylinder heads... where on a VAN you have to pull the engine cover, sorry.. there are a pair of wires that come out of the harness with ring terminals for this.


please examine the distributor cap.. the rotor.. man do those burn thru also.. the cap terminals burn up. the center carbon also.. but before you throw anything back on.. grab your flash light.. aim it right down at the top of the reluctor.. that is the star shaped device on the distributor shaft.. the second layer is a ceramic magnet.. if its cracked.. you will need to change the distributor..
hopefully you will find a OEM brand.. not a delco.. and OEM or OER that is reman by A1 Cardone. they started using replacement distributor shafts on these with a solid reluctor.. no rivets.. no magnets to crack.. far superior AC wave form output.. i get them at Autozone.. i don't know who else carries them. probably a lot..
the distributor cardone reman part number is.. 1995 Chevrolet Truck G30 1 ton Van 5.7L TBI 8cyl Part Number: 30-1830 Alternate Part Number: DC804EFI

if the upper bushing is worn. the shaft will have side to side play.. where the pole pieces actually touch the pickup coil poles.. i have had them so bad it sounded like the valves were clicking.. up and down play is allowed ..

if you go to replace the distributor.. preset the engine please.. print this section out.. with your remote starter button hooked up and hopefully its one of the better ones that has a push button on the end.. place that in your hand upside down.. with it clenched in your fist.. bump your fist like you are playing rock paper scissors into something to push the button into that object.. floor board.. engine .. something solid. this will allow you to move the crank fractionally.. figure out where the number one wire is in the cap.. get the rotor almost pointing in that direction.. use tiny bumps to get the reluctor tip to align perfectly with the pickup coil poles.. if the rotor is pointing in the proper direction. and the poles are lined up .. if you go up front and look at the timing marks.. G Vans have a special timing pointer and additional mark usually.. that should be aligned at base timing.. what ever that is... 0TDC or 15 BTDC. could be either.. i try not to remember the timing settings i always look them up. or check the emission label. i have a smog book that keeps getting put away that lists them...

back to the distributor.. if the pole pieces are aligned.. the rotor pointing in the proper direction . the crank marks should be at base timing.. you can now remove the distributor. work on it. use it like a baseball bat and swat rocks with it.. but when you install the new one. you can actually drop it in.. you may have to use a long screw driver to reset the oil pump shaft.. but if you get it to seat.. you can turn the housing to align the pick up coil to the reluctor teeth.. lock the hold down plate and reassemble. base timing will be so close its crazy..

i do that when i work on any distributor.. i can preset the engine/distributor.. pull the distributor.. work or change it.. put the new one in.. sometimes i use the remote starter button to spin the engine to get it to drop but only with the distributor in. so i know which crank turn i am on.. i bring the crank to base timing marks.. i turn the housing to align the pole pieces.. i lock the hold down plate.. reach thru the open window and start the engine without needing to turn the distributor.. this blows most people away.. they have never seen anything like that.

its just that with the crank set to base timing.. if the pole pieces are aligned and the rotor pointing to the number one wire.. the timing is going to be within 2 degrees. its closer if you don't turn the crank backwards.. and you have to be on the #1 Compression stroke not the number six..

~~~~~~~~~~~~

next thing that can cause your issue.. CLOGGED CATS.. easy to tell.. unscrew the oxygen sensor.. unplug it.. start the engine.. rev it up.. what happens.. does it run good now.?? will it rev.. if so.. your cats may be clogged from the excess carbon from combustion or the crud from the seafoam treatments.

another thing.. bad MAP Sensor. that domino shaped device with a green 3 wire plug. and a vacuum hose..

you might also want to search out and just replace the engine coolant temp sensor and its pigtail. at az.. its part number SU102.. from wells also the same number.. or an AC delco Part # : 213-52 that is both sensor and pigtail.. usually under 20 bucks for the pair.. either can go bad.. since you have a hard one to work on..

you may want to breeze thru this forum post i found.. http://forums.superchevy.com/corvette-fever/70/8585187/c4-corvettes/whi ch-used-scan-tools-for-82-to-94-corvettes-with/ that guy knows scan tools.. who ever he is..
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Arnold
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PostPosted: Fri, Jun 05 2015, 12:27 pm    Post subject: Reply with quote

wayne petty wrote:
the IDLE air control valve does NOTHING ABOVE idle.. other than act like a dash pot to prevent high manifold vacuum when you take your foot off the gas and close the throttle..

please verify the spark .. before you go anywhere else.. i have changed so many ignition coils on GM TBI and Vortec motors i cannot count them..

the sides of the coil will have marks like this grey area or worse on the sides
http://i.imgur.com/LIyPczv.jpg this is where the high voltage spark leaks out ..no high voltage spark.. you won't have enough voltage to flash over the spark plug and rotor to cap gap and the engine will misfire or die...

how long does it take to check for spark.. a minute... how long does it take to change a coil on a TBI or Vortec V8... under 15 minutes.. i did a vortec V6 coil in a 98 GMC safari in 12 minutes last week. but i already had the engine cover off so that is kinda cheating.

how to tell.. use a spark gap tester.. 8 bucks.. at most parts stores.. not the neon bulb type.. the adjustable gap type.. if your coil looks like above.. don't bother . just replace it.. you can pull the coil wire out of the cap.. position it 1/2" from something metal and crank then engine.. if you only get a dull orange spark.. replace.. if you get a SNAPPY BRIGHT BLUE spark... then the coil may be OK.

a few things that will make your truck also just die..

bad ground connections.. there is a computer to engine ground connection for the TPS and some of the other sensors on either the thermostat stud or the stud directly behind the thermostat. i have to replace that ring terminal the first time i work on so many TBI and Vortec engines another uncountable number..

but the Computer MAIN ground is to the back of the cylinder heads... where on a VAN you have to pull the engine cover, sorry.. there are a pair of wires that come out of the harness with ring terminals for this.


please examine the distributor cap.. the rotor.. man do those burn thru also.. the cap terminals burn up. the center carbon also.. but before you throw anything back on.. grab your flash light.. aim it right down at the top of the reluctor.. that is the star shaped device on the distributor shaft.. the second layer is a ceramic magnet.. if its cracked.. you will need to change the distributor..
hopefully you will find a OEM brand.. not a delco.. and OEM or OER that is reman by A1 Cardone. they started using replacement distributor shafts on these with a solid reluctor.. no rivets.. no magnets to crack.. far superior AC wave form output.. i get them at Autozone.. i don't know who else carries them. probably a lot..
the distributor cardone reman part number is.. 1995 Chevrolet Truck G30 1 ton Van 5.7L TBI 8cyl Part Number: 30-1830 Alternate Part Number: DC804EFI

if the upper bushing is worn. the shaft will have side to side play.. where the pole pieces actually touch the pickup coil poles.. i have had them so bad it sounded like the valves were clicking.. up and down play is allowed ..

if you go to replace the distributor.. preset the engine please.. print this section out.. with your remote starter button hooked up and hopefully its one of the better ones that has a push button on the end.. place that in your hand upside down.. with it clenched in your fist.. bump your fist like you are playing rock paper scissors into something to push the button into that object.. floor board.. engine .. something solid. this will allow you to move the crank fractionally.. figure out where the number one wire is in the cap.. get the rotor almost pointing in that direction.. use tiny bumps to get the reluctor tip to align perfectly with the pickup coil poles.. if the rotor is pointing in the proper direction. and the poles are lined up .. if you go up front and look at the timing marks.. G Vans have a special timing pointer and additional mark usually.. that should be aligned at base timing.. what ever that is... 0TDC or 15 BTDC. could be either.. i try not to remember the timing settings i always look them up. or check the emission label. i have a smog book that keeps getting put away that lists them...

back to the distributor.. if the pole pieces are aligned.. the rotor pointing in the proper direction . the crank marks should be at base timing.. you can now remove the distributor. work on it. use it like a baseball bat and swat rocks with it.. but when you install the new one. you can actually drop it in.. you may have to use a long screw driver to reset the oil pump shaft.. but if you get it to seat.. you can turn the housing to align the pick up coil to the reluctor teeth.. lock the hold down plate and reassemble. base timing will be so close its crazy..

i do that when i work on any distributor.. i can preset the engine/distributor.. pull the distributor.. work or change it.. put the new one in.. sometimes i use the remote starter button to spin the engine to get it to drop but only with the distributor in. so i know which crank turn i am on.. i bring the crank to base timing marks.. i turn the housing to align the pole pieces.. i lock the hold down plate.. reach thru the open window and start the engine without needing to turn the distributor.. this blows most people away.. they have never seen anything like that.

its just that with the crank set to base timing.. if the pole pieces are aligned and the rotor pointing to the number one wire.. the timing is going to be within 2 degrees. its closer if you don't turn the crank backwards.. and you have to be on the #1 Compression stroke not the number six..

~~~~~~~~~~~~

next thing that can cause your issue.. CLOGGED CATS.. easy to tell.. unscrew the oxygen sensor.. unplug it.. start the engine.. rev it up.. what happens.. does it run good now.?? will it rev.. if so.. your cats may be clogged from the excess carbon from combustion or the crud from the seafoam treatments.

another thing.. bad MAP Sensor. that domino shaped device with a green 3 wire plug. and a vacuum hose..

you might also want to search out and just replace the engine coolant temp sensor and its pigtail. at az.. its part number SU102.. from wells also the same number.. or an AC delco Part # : 213-52 that is both sensor and pigtail.. usually under 20 bucks for the pair.. either can go bad.. since you have a hard one to work on..

you may want to breeze thru this forum post i found.. http://forums.superchevy.com/corvette-fever/70/8585187/c4-corvettes/whi ch-used-scan-tools-for-82-to-94-corvettes-with/ that guy knows scan tools.. who ever he is..


That is a ton of great info Wayne Very Happy

This thing has lost the ability to produce enough cranking vacuum.I am highly suspecting it is just too carboned up. I thought it might have been a bad cam..(that would artificially raise it) and in combination with other leakage..leveled it out to normal
Ya..one of the cylinders just leaks down like right now Laughing buids normal compression at a normal rate..at least it did when I checked it last.
Could be that enough clean out stuff has softened enough carbon to allow the valves to seat..I doubt it.Maybe there is a burned seat.That is what used to happen. Deposits on usually the back face of the valve..working their way down..finally close to/on the seat. Then hot exhaust gases blowing by and burning the valve at the seat.
I dunno..if I try it again..it is gonne have to have some cranking vacuum..before I go any further.

The Iac..does/did quite a bit above an idle on this thing. Laughing A couple of times after I had had it out and cleaned it..you could hear it hissing like crazy from quite a a big vacuum leak..as the valve was stuck..then it moved toofar the other way Laughing I cannot see it as a problem now. It could not leak enough to lead to a no vacuum crank.
When the iac was pretty freed up..that was the best it ran from idle up.

I am lazy when it comes to GM hei units. Stick another one in Laughing
I check them with a calibrated tester for Hei It is a little centre gap spark plug that has a clip attached to it. Stick plug lead in.Clip plug to metal. Spark. It has spark. I tested that already.I don't have an adjustable one. I found the adjustable ones good with points ignition..as head room seemed to be an issue. When hei came along..there was plenty of spark. I was stunned when I read what the likes of Jenkins did with just bone stock hei's. I used to have piles of them. I would get the curve info I needed/wanted..and could just get a particular " dist..or I could get the #'s for the weights and springs. Ditto for vac cans.
The coolant sensor was next on my list.
I don't think the cat was plugged..It seemed..to have plenty of power from above idle somewhat..and up..I mean that was only being revved up..not driven. Huge differences can occur there.
I had a vacuum gauge on it when it died.I idled it down..and the vacuum just kept dropping..dropped below 8..now next to zero on cranking.
Think I would rather replace the van than the heads on this one Laughing
I already went through the vac system on this truck.

Thanks Again Very Happy
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