For 3 years now I have been fighting a problem on my wifes 1997 GMC Jimmy 4.3L Automatic trans with 165000 miles.

I had replaced the ignition switch for a problem with the instrument lights flickering and then shutting off randomly but car would remain running.

Due to milage I replaced the plugs, cap, rotor and wires before the dieing started.

First time the car died was about 6 months after I replaced the ignition switch and we was on a 3 hour trip in the summer and the vehicle died like the key was turned off. After about 10 min it started back up and ran great but dies shortly after. I noticed the longer I would let it cool off the longer it would run before it died again. When we finally got back home I did not suspect the ignition switch but I rang it anyway and it rang good so I installed a new ICM "Ignition control module" from autozone. I also pulled the codes using my snap-on MT2500 scanner and it had code P1351 which is ignition control circuit high/low so I thought the ICM had to be the culprit. After a couple weeks it did the same thing. I rang the wires that had anything to do with the ignition and found nothing so I replaced the crank position sensor. After a couple weeks and the right conditions it died again the same as it always has. I then replaced the ignition coil even though it rang good but figured maybe when it is hot it is opening up. Again it died a few days later. I checked the fuel pressure even though it has nothing to do with the code P1351 and it was fine except that when I turn off the key the pressure drops faster than it should so I pulled the plenum off and check to see if the injectors were leaking and they did NOT show any indication they were so I put it all back together. Weather turned cool and problem stopped then wife went out one day and car would not start at all so I tought finally a hard fail so this will be easy now to fix, I found the fuel pump had died so I ordered a new fuel pump assembly and installed it and car was back up and running again. I hoped that might have been the problem all along so I waited till summer and sure enough the car died when it got hot again. I thought maybe the autozone ICM is junk so I had them warranty it for me and after installing the new one it died the next day. I figured maybe PCM is bad so I found one on ebay from a Jimmy the same as ours and after a few weeks it died. I thought maybe the ignition switch autozone sold me has been the problem all along so I had them warranty it for me and I installed the new one with no help. Only thing I have not replaced is the the cam position sensor but I was told that would not make the car die but I am not so sure. I am getting really frustrated not to mention my wife doesn't like to go anywere because she is afraid of being stranded. Any new ideas or help would be great.

Recap of what has been replaced.

IGNITION SWITCH=Twice
PLUGS
CAP
ROTOR
WIRES
ICM=twice
PCM
CKP
COIL
FUEL PUMP

 

I had an older car that did the same thing (mid 80s) and it turned out to be the coil. I found out later that they are really affected by heat, and when they are going bad they will only work til they warm up. The only other thing that is affected by heat is the ICM, and it sounds like you've beaten that horse. Get yourself a cheapo spark plug wire tester and keep it in the truck and when it dies, check for spark.

 

Actually I did replace the coil I just forgot to add it to the list. I have since added it to the list.

One thing I have been wondering is if the autozone ICM's are just junk and can't take the heat the way the Delco units can. The bracket the ICM mounts to gets so hot you can't touch it with your bare hands so I have since built a huge heatsink and have attached the ICM to it and have been driving now for 2 days and everything is good so far. I will post back if It seems to have fixed it.

What sucks is autozone does not carry a better ICM so I can't ask them to upgrade me to a better unit. The only option I might have is ask autozone to refund my money and buy a AC delco unit but I bet they wont do that for me.

 

I thought I fixed my stall issue (97 blazer) with ICM+coil, but now I'm getting down to my last theories, too. I just did the ign switch and I'm waiting for a stall any day now to confirm the old one wasn't my issue.. I, too, wonder if my aftermarktet ICM is maybe not capable of handling extreme heat?

PCM?? You say the truck has to cool for a few minutes before a restart? Perhaps the second-hand unit has the same heat problem as your original? I've heard you can try pouring water over the case after a random hot stall to determine if that's the culprit.

When it stalls and won't restart, does the fuel pump prime, or are you getting dash lights only?

Have you cleaned&inspected your EGR before? (probably not your issue)


You can apply 12v to the fuel pump socket on the harness and it should run the pump (on my 97 blazer it's the top drivers side harness, pin 1 green/white wire). If the key doesn't run the pump, but jumpering this pin does, the only culprits are VCM or ignition switch related (probably VCM since you're on your third switch!!). If you plug the harness back in and the key still doesn't run the pump, bingo! (tough to verify depending on how long you are typically in a no-start situation)

97 blazer VCM pinouts (click on the "see full conversation" link to get the pinout tables)

good luck!

 

Yea I thought about the second VCM. The fuel pump will prime with key. Everything seems to work when it dies except it will not start, it acts just like the ICM overheated. I am still waiting to see if I get a call from the wife bitching at me because the car died again and then I will know if the heat sink mod worked. I am still thinking about just spending the 100 bucks and buying a delco ICM.

 

You can get better ICMs and Heatsinks. Go to Summitracing.com and there part #s are ACF-10474610 for the Heatsink, (AC Delco, $17.99) and MSD Module W/rev limiter # MSD-83647 for $92.95. Thats a lot cheaper than GMs $300.00 unit, and I trust MSD. In fact I am going to order one now (you never know when they're gonna go) I'll let you Know how it works. Also it is a good idea to keep an extra in your rig, I've had mine go out driving down the road.

 

Thanks for the info however the ingnition module you listed is not the right one for my application. Mine is like this one. http://www.summitracing.com/parts/ACF-D579/

The heatsink on summits site looks just like the factory one that I replaced with my upgraded computer CPU heatsink. Infact I see that the maker of the heatsink from summit is ACdelco so it is probably the OEM heatsink that it came with.

So far the Jimmy has not died since I have done the upgraded heatsink mod and the outside temps have been about 103 so I have my fingers crossed that this has finally fixed it. Below are a couple pics of what the heatsink looks like.

Edit:
Just out of curiosity I hit the heatsink with my laser thermometer after the wife just got back from shopping and it was at 177 degrees. Does anyone no what the max rated temp is that the ICM should be able to handle. Unfortunately I never got the temps with the factory heatsink so I can not compare the two to see how much cooler this one is running.

 

Man, I just had a nightmare of an afternoon with this stalling issue. Probably 10 stalls in an hour (city & hwy driving) after I had driven an hour.

Are you showing any relevant trouble codes?
I had advance do a scan for me on my way home and one of the codes I have stored is P1351 (ICM high voltage).

The sticky post on P1351 sounds like this may be due to faulty wiring ???
https://blazerforum.com/forum/diagnostic-trouble-codes-dtcs-49/p1351-explained-35134/

Oh joy, at least I have something to look into that doesn't involve swapping parts! =).

 

Sounds exactly like my problem and yes the code that always came back was P1351. I rang every wire that had to do with ignition or computer and even wiggled the wires as I rang them and did not find any issues with wiring.

SO far the added super heatsink has seemed to cure the problem, we havent made any trips over about 1-1/2 hours yet but the outside temps have been above 100 for the past few weeks and the vehicle has not died once. I still have my fingers crossed that this problem is fixed.

If you decide to try a ICM do NOT buy the one autozone sells, I would spend the money and get a ACdelco unit they are about $99.00 online and I paid $80.00 plus tax at autozone for there brand that can't take the heat the way ACdelco units can.

 

Yeah, x2 on the delco ICM advice for anybody reading this thread. I think I might try to beef up the heatsink

I decided to switch out my crankcase position sensor with one from a junkyard (I have a 97 with 170,000 and this sensor came out of an '02 at u-pull-it yard). For $5 it's worth a shot even though I didn't have a code for CKP. It's $50 new.

I still need to do the procedure of checking voltage on VCM pins while molesting the ICM+CKP wiring harnesses... been busy fixing other stuff. We're about to have cooler weather and I'm going to Texas for a month, so it could be a while before I might determine the CKP sensor wasn't the problem.

Please post to this thread if it stalls again.