87 TBI - Sporadic Starting

[routha]

I couldn't find a brand name on it. .

Allegedly the truck had "51xxx original miles" but I think the guy was full of s*** and it actually had a 151,000. I assumed it was the original one.

 

[1987 GMC Jimmy]

They told me the same thing when I bought my Jimmy 83,000 original miles, but the Carfax had 183. I must look stupider than I am because even though I think it was a good one, and I wanted one real bad, I wasn’t born yesterday.

 

[routha]

Well I installed a new module on Saturday and fired it in the garage a few times. It took longer than usual to fire but not unusually long. I never took it for a drive until today.

I started it and backed it out of the garage to warm up (Minnesota winter) and it idled for about five minutes and died.

I started it again and put it in drive to pull into the garage and it died once it went into gear.

Any suggestions?

I went to O'Reillys and Auto zone to have the old module tested but neither one could because the machine was down or they didn't have the right end.

I'm going to put the old one back in and see if it will idle with that.

I'm looking over the troubleshooting guide at the moment as well.

The guy at o'reillys suggested a distributor cap

 

[hatzie]

Have you downloaded the GM Light Truck Emissions and Driveability manual for 1987? For that matter the Wiring Manual, the Unit Repair Manual, and the Service Manual are available to download as well. Look in my signature.
The 1987 GM wiring manual is a bit nasty to read but it's not a one-size-fits-all wiring diagram like the Haynes manual either. You need to open to the RV chassis section. It's a full line wiring manual that includes the early CK (T400) and the ST G P & M chassis wiring diagrams too.

I doubt it's the distributor cap. Replacing the cap and rotor won't hurt anything but don't expect them to fix an intermittent like this. The Standard Motor Products Blue Streak cap and rotor sets used to have brass terminals. They were top shelf parts.

The coil maybe. I've had them go intermittent. I'm not sure if the ECM will get pulses from the ignition module with a dodgy coil or not. The AC Delco Pro ignition coil is D503A

Standard Motor Products are a top tier manufacturer. I think I'd still get an AC Delco Pro D1943A or the OEM GM Delphi DS10059 ignition module. They're the same price. Delphi is what your truck came from the factory with.

 

[hatzie]

The other thing to consider getting is a cheap Dell D620, D630, D820, or D830 Windows XP laptop on eivlbay. I just bought 2 for $120. They typically cost between $60 & $150 for tested working units. I like the D6xx and D8xx laptops because they run XP and have real RS232 Serial ports for talking to ancient test equipment and ALDL ECMs and the batteries are cheap and easy to find. Pay attention to processor speed, memory size, HDD size, and Screen res. More is better and they don't necessarily cost more to get more because they are so old. If you don't need XP they can be found with Windows 7 32bit pre-installed but you really want as much processor HDD and memory as you can get because these are old dual core machines.

You can hack one of Craig Moats ALDL cables together or buy a slick new Red Devil River or 1320 Electronics USB to ALDL cable for around $50. I would buy one if you don't have electronics fabrication experience.
WinALDL or Tuner PRO RT with the correct ADX file will talk to your TBI ECM. They're both free. They only listen they don't command solenoids etc like a Vetronix Tech I or Tech 1A but they don't cost $1000 plus either.

 

[1987 GMC Jimmy]

When it dies, is it instantaneous or does it slowly sputter out and die?

 

[routha]

When it dies, is it instantaneous or does it slowly sputter out and die?

Instaneous. . As soon as you come to stop basically.

I swapped out the new Standard module and put the old one back in (brand unknown). I let it idle for 5-10 minutes without issue. i drove it for approx 5 miles and got it up to operating temp and highway speeds without any issues. I parked it in the garage, shut it off, and started it 5 minutes later and it fired right up.

I'm going to look into what Hatzie said and also pick up a Delco or Delphi module and go from there.

I'm at a loss.

 

[1987 GMC Jimmy]

I’d be checking for spark whenever it decided to act up. That’s strange, but there’s no shortage of strange problems here. If you could find it not sparking for sure, that would really narrow down your list of options.