So here is my saga. I have my 86 that I bought new…. Garage queen..12,000 miles. I was warming it up one day and it just shut off. I restarted it and drove it and all was ok. Then several weeks later I went to take it out and the same thing happened. No SEL light or codes. Sometimes it’s ok sometimes not. I am trying to diagnose the problem with no luck. It will start up from cold and when it gets to about 170 temp strange things happen… the idle will kinda jump around and the radiator fan will cycle on for several seconds and then go off with no rhyme or reason. It can sit there and idle and the fan can cycle at 232 /217 several times over 20 minutes or so and all the sudden it will shut off…. And when it shuts off, if the fan is running that will die as well. It doesn’t set a SEL light but it did set a code 42- 1 time and a code 34- 1 time. However after running for 4 or 5 minutes I shut it off and went to pull the codes again and they were be gone. I’m thinking the ECM has a problem but that is just a guess. When nothing weird is going on it runs perfect….. When it starts to act up it acts like it is missing a little and won’t idle… but 30 seconds later all is well again. I checked the ohms on all the injectors both hot and cold and they are within specs 16.2 to 16.8 Ohms. Not quite sure how to continue the diagnosis.

 

Corrosion on grounds, or battery. Fuel quality since car sits too much. Carbon build up in throttle body. MAF relays. If you choose to replace ecm prom needs to be transferred, it's under a small door on ecm.

 

No corrosion on anything.... I checked all the grounds that I could get to and they were all tight and clean. The fuel is fresh. Zero carbon build up on the TB. Not sure about the MAF relays but I would "assume" that since this is an intermittent problem that they are fine. I'm going to try to upload 2 videos. ( well that didn't work, the files are to large) The first one is what it does.... will run for 15 plus minutes warming up with no problems. In this video it was running from cold and dies several seconds after the main fan comes on. When it dies the fan also cuts off. I'm not 100% sure wither it dies as the fan cycles off or at some point before it shuts off. The 2nd video I decided to stick a screw driver on the adj screw to raise the idle to 1300 to see what would happen. After several minutes it starts stumbling, the fan actually seems to go up and down rpm wise, the engine rpms drop to about 800 and stay there for the rest of the video.... remember it was at 1300 and nothing changed as far as the throttle plates go. After the video ends I took the screwdriver out and it stalled. Through all of this it never set a code. Not sure how to post the videos since they are to large.

 

Kevova hit on the things I usually think of a failure on the ground side, but what if it's a failure on the power side. Corroded fuse, bad supply and the fan kicking on is enough to shut down ECM

 

So today it was nice so I took it for a short 15 mile drive. Ran perfect came home and parked it. Did some much needed yard work and it sat for about 3 hours. I went to start it the fan came on as soon as the key went to on and the engine started and shut off.... got it running again and it was running rough. I kept the idle up at about 2000 and after a couple minutes I saw the SES light Flash a couple times so I let it idle down but it stalled... It would not idle. So i figured I would check for codes.... however with the key on engine off the SES light wouldn't come on. It's supposed to be on with the key on engine off. I tried to pull a code but it wouldn't flash even the 12 code. I let the car sit another 3 hours and now the SES light comes on and If I try to pull a code all I get is the 12 code. I'm kinda leaning the ECM is bad. It's driving me crazy...lol

 

Got an ECM out of an 87 Auto car and swapped it in with the 87 prom and she runs like a top again.

 

It would be a good idea to at least check the memcal labels on both of the proms to determine which bin files are programmed on to each prom, then decide which prom makes the most sense to use in the car.

1986 is a $32 masked bin, while 1987 is a $32B mask which includes some minor programming and addressing changes with respect to $32. Spark advance and TCC settings (axle ratio dependent) will likely be a bit different between them. I assuming that the car and both proms are auto transmission proms.

If you post up the broadcast code for each prom, I can help you compare them if I have copies available.

 

Thanks for your help. So my original 86 prom is AANL4045 and the 87 is ABTD0731. My 86 is an auto I think the 87 was also.

 

Here's some info:

32 AANL 16.00 KB 1986 31397 16064044 1227165 4045 2241 YB L98 5.7 MD8 AUTO G44 (3.07 gear)
32 ABTD 16.00 KB 1987 31565 16070729 1227165 731 7761 YB L98 5.7 MD8 AUTO GM1 (2.59 gear)

I do have copies of both bins, but need to do some work first in order to compare them in a meaningful way. The masks are different, so the parameters don't really line up side by side. I will see what I can do.

Does the car have iron heads? AANL is labelled as an iron head bin, but not sure that this is really correct. If so, ABTD may be a bit aggressive spark advance wise, since it was designed with aluminum heads in mind.

 

Thanks again..... it is a late 86 so it is aluminum headed....... I did notice on my drive that the upshift light kept coming on and I'm sure that is from the different gearing with the bins..........I'll try to make this as short as i can...lol My whole deal with getting the car running right is I want to do an engine change out. I wanted to make sure it was running normally before I did any more so I wasn't scratching my head as to if it was something new that i did or an old problem cropping up. So i already put a Dana44 3:45 in it with new half shafts etc, and I changed the speedo gearing to try to match what I have. My short term goal is to swap in the Dynamic EFI setup, which I have, and get somewhat used to tuning with the stock engine. I have the wide band set up as well and will hook that up too. Then when I am somewhat comfortable with that...... I have a 396 stroker with AFR heads and a SuperRam all done sitting on the engine stand waiting to go in. Since I have never done the computer tuning it will be a vertical learning curve for me for sure but I'm sure once I start actually doing hands on it will come, abet slowly, I'm sure. There is a guy on ThirdGen that lives in NJ and is willing to come and help me which is awesome. Everybody is always willing to help which is great. I am always amazed at your knowledge when reading all the posts in regard to the tuning stuff.