87' R10 TBI 350 shuts off when driving. HeLP

[gmbellew]

I got tired of following the troubleshooting guide after going about 3/4's the way thu it and finding nothing wrong... So I just replaced the distributor coil like was told earlier and also swapped the ICM just because I had the extra ones in a box. It Started... I wonder if the new (standard) ICM went bad?? But happy to say it is running again! Now have to do the timing and button it back up! Hoepfully what ever I did fixed the random cut out while driving! And will replace the pigtail to the coil when it arrives on Thursday!

I try to only use AC Delco parts for any engine sensor or management, including the ICM.

 

[Hunter_Michael]

I try to only use AC Delco parts for any engine sensor or management, including the ICM.

I definetly will in the future! Thanks for the help!

 

[Knuck55]

Throw a fuel pump relay at it. Happened to me.

 

[YakkoWarner]

This thread is near and dear to my heart because my 1989 suburban (R2500/TH400/454) has started doing pretty much the same thing. I had to replace the whole distributor 3 months ago because the pickup coil was bad (no spark no fuel pulse) and it was in rough shape inside (corrosion), so it has a brand new distributor, pickup and ICM. Only seems to die on throttle lift or idle, when it dies no fuel OR spark until key cycle, then starts right up again. I've replaced all the sensors that should be relevant (TPS, MAP, O2, TEMP, OIL) to no effect; tank and pump were replaced when truck was purchased 2 years ago (filter replaced last week). Runs properly even with the fuel pump relay disconnected which confirms oil pressure switch functionality. Previous post recommends pump relay swap which I have done (results still pending), but I'm not 100% sure how the pump relay could cause the spark circuit to go dead since they aren't in any way interconnected.

 

[gmbellew]

This thread is near and dear to my heart because my 1989 suburban (R2500/TH400/454) has started doing pretty much the same thing. I had to replace the whole distributor 3 months ago because the pickup coil was bad (no spark no fuel pulse) and it was in rough shape inside (corrosion), so it has a brand new distributor, pickup and ICM. Only seems to die on throttle lift or idle, when it dies no fuel OR spark until key cycle, then starts right up again. I've replaced all the sensors that should be relevant (TPS, MAP, O2, TEMP, OIL) to no effect; tank and pump were replaced when truck was purchased 2 years ago (filter replaced last week). Runs properly even with the fuel pump relay disconnected which confirms oil pressure switch functionality. Previous post recommends pump relay swap which I have done (results still pending), but I'm not 100% sure how the pump relay could cause the spark circuit to go dead since they aren't in any way interconnected.

I'd be looking hard at the new ICM or some sort of electro interference from a cracked distributor cap or a plug wire touching an ICM or any of the ECM sensor wires. With it doing at idle or deceleration (throttle off, slows it down) it might me something that is making contact under certain conditions. Might try wiggling the harness all around while it is idling and see if you can reproduce it

 

[Ricko1966]

This thread is near and dear to my heart because my 1989 suburban (R2500/TH400/454) has started doing pretty much the same thing. I had to replace the whole distributor 3 months ago because the pickup coil was bad (no spark no fuel pulse) and it was in rough shape inside (corrosion), so it has a brand new distributor, pickup and ICM. Only seems to die on throttle lift or idle, when it dies no fuel OR spark until key cycle, then starts right up again. I've replaced all the sensors that should be relevant (TPS, MAP, O2, TEMP, OIL) to no effect; tank and pump were replaced when truck was purchased 2 years ago (filter replaced last week). Runs properly even with the fuel pump relay disconnected which confirms oil pressure switch functionality. Previous post recommends pump relay swap which I have done (results still pending), but I'm not 100% sure how the pump relay could cause the spark circuit to go dead since they aren't in any way interconnected.

Your fuel pump relay has nothing to do with it. It's a redundant circuit as you already proved by removing the relay. Just a WAG by someone to send you down a rabbit hole.

 

[YakkoWarner]

When logic and reason fail, sometimes the WAG is all we have left. Either that or appealing to supernatural powers. I'm kind of to that point on this one. Even British car electricals obey the laws of physics and cause-effect relationships.

 

[YakkoWarner]

I'd be looking hard at the new ICM or some sort of electro interference from a cracked distributor cap or a plug wire touching an ICM or any of the ECM sensor wires. With it doing at idle or deceleration (throttle off, slows it down) it might me something that is making contact under certain conditions. Might try wiggling the harness all around while it is idling and see if you can reproduce it

These are all sound ideas, which unfortunately I had already investigated. The new distributor came with a new cap and rotor, and since I had a spare unused ICM handy (purchased prior to discovering the actual bad pickup coil in the original distributor), I tossed that in (and yes I used high quality thermal paste) which also did not solve anything. Plug wires are routed cleanly away from the distributor signal wires (is there an award for Zip-Tie engineering?), and I have also ensured solid grounding by adding an additional ground wire from the coil bracket directly to the firewall (this was installed in response an ESC error I was experiencing last year and solved that problem nicely). When the distributor failed I also replaced the coil - since I didn't know what caused the distributor to fail I was hedging by bets) - I swapped the original coil back on which also did not resolve the random shutdown. I checked fuses, shook the wires while running and could not induce the failure - but had it happen twice just sitting in the driveway in park while not touching anything.

 

[gmbellew]

does it die suddenly, or die sputtering like it ran out of fuel?

does your SES light work, any stored codes?

might try to diagnose the ignition system next time it happens before you cycle the key? run through the check in section 6 of the emissions and drivability manual.

 

[YakkoWarner]

It dies suddenly, as if the key had been shut off (except all the instruments continue showing readings). My truck didn't come equipped with a tach so don't know what does or doesn't happen on that tach send wire of the coil when it dies. If it dies while actually driving at a decent speed (45-55mph), I've had the engine continue to be spun by the transmission (which I always thought was impossible with an automatic until I observed it happening) and still have oil pressure showing, so I am pretty sure it is not the key switch losing contact but I checked the connectors under the instrument panel anyway to be sure. I am pretty sure this is not a fuel delivery malfunction.

SES light does work, only stored code I get is an intermittant 44-LeanCondition which is not consistant with the shutting down (sometimes get the code and no shutdown, sometimes shutdown with no code, sometimes both) - I am pretty sure a lean condition is a seperate issue which shouldn't result in a loss of spark or injector pulse signal, but my understanding of how these systems interact is clearly not complete. I have pulled plugs and they appear to be buring normally, not the bleached and cracked overheated ceramic you'd see on a consistant lean running condition.

I need to hunt down a copy of that "Emissions And Driveability" manual, that is one I don't seem to have a PDF of and probably should.

 

[gmbellew]

All the GM manuals are in the reference library on this forum. check the home page.

 

[YakkoWarner]

Obtained!!! Thanks.....

 

[chairmnofthboard]

Have you considered a bad ignition switch?

 

[Olegmbuilder]

I've learned over the years with these old 80's something chevy trucks/blazers that they are really finicky about replacement parts. I discovered that using anything other than AC Delco or GM original replacements those off brands don't work to well. I had a engine shut off problem like this and come to find out it was the off brand replacement fuel pump and sending unit from a my local auto parts store. I ordered a direct original GM replacement from the GM site plugged it in and never had a problem with the no start issue again. Go figure. Hope this helps.