88 GMC 1500 no start

[Double Snowman GMC]

OK now, my no start is solved thanks to the Forum telling me where to focus! Woo Hoo!

I went back to check the Pickup coil and found the red connector to the ignition module loose (which I installed in some haste when I swapped back to the original 1988 ignition module)

So I guess I’m somewhat confident that this no start problem was the new/faulty ignition module I installed 6 months ago??

Buoyed with this success to get back drivable I plugged in the ALDL cable while the engine was idling ....and it immediately sped up 50 rpm.

Why does plugging in an open ended data cable shut down the truck one time and then increase the idle the next time??

I do see 4 rows of data in WinALDL, but it seems like I should be using Tunerpro??

Thanks for all the help so far,
Bob W

[tayto]

i assume the red connector is the pickup coil wires that plug into the 2 pins on the back of the ICM. I've had a moates OBD1 cable for close to a decade now and never had the issues you are having. does your cable have continuity between terminals A & B?

[Double Snowman GMC]

Ya, the pick up coil to ICM was loose on the swapped in ICM
No continuity between A & B terminals on the data cable.
Is Tuner Pro the best software for my application?
It seems like my truck is somewhat haunted.....with a mind of its own

[Double Snowman GMC]

PS. My IT guy (son) says we tried to download Tuner Pro off the internet, but our antivirus did not like it.

It also showed “missing DLL” errors.

[PlayingWithTBI]

No continuity between A & B terminals on the data cable.

Possibly it has a 10K Ohm jumper between A & B for older vehicles and TPI? My ALDL cable has all 3 options, open, jumped direct, and 10K Ohm resistor.

[tayto]

that's what I was thinking, maybe in field service mode. i remember messing around with an old handheld obd1 scanner and when you put it in field service mode the rpms went up. this was 15 years ago and I probably only played around with it for 30 minutes

[Double Snowman GMC]

Of course you guys are correct as usual, my cable does have the 10k resistor. So I remove it and can see a few rows of data in WinALDL.
Where should I focus on the data to cure my original stall problem?
I would download TunerPro but my antivirus doesn’t like it.

Happy New Year

Thanks again,
Bob W

[tayto]

we need more information, when does it run rough? cold? hot? on acceleration? after a highway run? all the time? I would suggest getting an adapter so you can check fuel pressure. i would suggest posting a log here of when the vehicle is running rough. ignore your anti-virus and install tuner pro.

[PlayingWithTBI]

we need more information, when does it run rough? cold? hot? on acceleration? after a highway run? all the time? I would suggest getting an adapter so you can check fuel pressure. i would suggest posting a log here of when the vehicle is running rough. ignore your anti-virus and install tuner pro.

^^^What he said, YMMV.

Edit: I have Malware Bytes and don't have any problems with TunerPro RT v5xx on my laptop.

[Double Snowman GMC]

Problem: stalls out at idle consistently. Worse when hot, I can barely keep it going in neutral at a stoplight with the two foot driving method. Lately it’s gotten progressively worse, it feels “electrical” like it comes on quick.

Work done so far:

New fuel pump, filter, rebuilt TBI with higher pressure spring (I did check fuel pressure at the TBI)
Two new injectors
New MAP sensor
New coil
New Idle air controller
New temp sender
New throttle position sensor
Good egr
No obvious vacuum leaks

120k original miles, passes Cal Smog easily but puffs a little oil smoke at start up

Based on the latest info, I have ordered a new GM ignition pickup coil and see if that helps.

[dave w]

The attached pictures below are screen shots from TunerPro RT. WINAldl is a good program. TunerPro RT is a better program.

Increasing fuel pressure might not be a good plan for a stock engine?? The stock chip is programmed for stock fuel pressure. Increasing fuel pressure to much will cause the engine to run rich, maybe even to the point where excess fuel is washing the piston cylinder walls of oil. If your oil smells like gas, then it's a sure sign the engine is running to rich.

I would use the information from TunerPro RT to determine if the engine is running to rich, but a the foul smell of gasoline in the oil is almost as accurate as TunerPro RT data to determine if the engine is running to rich.

dave w

[PlayingWithTBI]

Maybe I missed it, did you replace the ICM too? A bad coil can take out the ICM. Get a good quality one like the AC Delco 1948A (IIRC).

[Double Snowman GMC]

Ya, I replaced the original ICM in May 2020 with Standard Motor Products ICM. Apparently, and coincidentally, this replacement failed when I plugged in my ALDL cable (with 10k resistor).

Now I have the original ICM re-installed (which runs).....but I don’t trust the pickup coil. I have a new pickup coil & ICM on order (both GM).

I had replaced the distributor about 5 years back with a cheapie parts store model, so now I suspect the pickup coil.

I guess this all makes sense?

[tayto]

did you get the throttle shafts bushed when you rebuilt it? I have no seen a unit in the last 10 years that hasn't had play. Granted usually only the bad ones cause running issues. How do you know EGR is good? i use to have a block off plate to eliminate the egr valve all together. A bad valve will cause poor/rough running @ idle is the only reason I mention it. I assume you have verfied the basics here, spark plugs (i only run delco), spark plug gap, wires, cap & rotor? do you have a datalog for us to look at yet?

i see you say 2 new injectors, did you save your old injectors? i have found getting the old ones cleaned and flow tested are better than what the aftermarket supplies.

[tayto]

Increasing fuel pressure might not be a good plan for a stock engine?? The stock chip is programmed for stock fuel pressure. Increasing fuel pressure to much will cause the engine to run rich, maybe even to the point where excess fuel is washing the piston cylinder walls of oil. If your oil smells like gas, then it's a sure sign the engine is running to rich.

some probably won't agree with me but i think this is a BS myth. a stuck injector will cause this but even 10:1 isn't going to hurt anything aside from maybe fouling plugs. maybe if it was to the point that they aren't lighting the mixture MAYBE it would wash the walls down but a poor or not running at all engine should be evident before things get this bad. I do agree that he doesn't need the stiffer spring if his engine is stock. I personally like to run 13-15 psi on stock setups vs the "recommended" 9-12 psi if the pump will allow it.