87' TBI timing question

[johns87]

First time posting, thanks ahead of time.

I got my dad's 87' Silverado and was starting to clean it up for the 8 years it sat in the driveway. After a couple new fuel tanks and pumps everything started right up. It was was having idle issues and stalling and decided to refresh things up some, well and squirrels had chewed up some stuff. Once I got started I ended up replacing TPS, MAF, IAC, temp sensors, rebuilt throttle body, various hoses, new distributor, coil, plug wires plugs, and a few other things I can't remember right now.

Everything seemed to be going good and been trying to set the timing. I unplugged what I think is the timing ecm wire (tan with black stripe wire w/plug near the drivers firewall) to set the timing. The truck is really stumbling, rough idle but when I jump out to set the timing it seem to adjust and run smooth. Almost like the ECM is compensating, but it should be unplugged. I set the timing, since it would adjust some but like I said it was pretty smooth. Turn the truck off, plug it back in, start it up, same thing. Rough idle, a few seconds later it smooths out. I unplugged it again, start up , same thing. Rough idle check the timing a little off, fine tune, plug in, restart same rough idle for a few seconds. I'm starting to feel like I am in ground hog day or something. Any ideas anyone?

 

[74 Shortbed]

Welcome to the site, you came to the right place for info, but not from me you wouldn't want to hear it, lol.

 

[johns87]

I will admit, this site has helped me so far in all I have done. Been lurking around it for a few months now.

 

[4WDKC]

wait did you do the IAC reset procedure?

 

[johns87]

Do I need to do that after i unplug the timing wire? Initially I reset but this weekend, I rebuilt the throttle body again. I was getting a high idle and traced it back. Figured one of the new gaskets wasn't sitting right. But, I did not reset it this time...

Off to try that...

 

[4WDKC]

Do I need to do that after i unplug the timing wire? Initially I reset but this weekend, I rebuilt the throttle body again. I was getting a high idle and traced it back. Figured one of the new gaskets wasn't sitting right. But, I did not reset it this time...

Off to try that...

That only needs to be done when replacing the IAC or if you change the pintle (sp?) position while cleaning it.

 

[johns87]

That's what I thought, but went ahead and did the reset again. Started it up and it had a really rough chugging sound, even a little bit of a backfire sound. After a few seconds the idle picked up and ran better. I let it warm up and the idle slowed back down. Set the timing again, plugged the ECM plug back in. It still starts the same way, rough chugging like for a few seconds.

Anyone have any ideas now?

 

[MrMarty51]

After adjusting the timing, did You disconnect the neg battery cable for a while ?
It will have to go through a learning procedure after starting it again.

 

[4WDKC]

That's what I thought, but went ahead and did the reset again. Started it up and it had a really rough chugging sound, even a little bit of a backfire sound. After a few seconds the idle picked up and ran better. I let it warm up and the idle slowed back down. Set the timing again, plugged the ECM plug back in. It still starts the same way, rough chugging like for a few seconds.

Anyone have any ideas now?

When you replaced the IAC did you notice if inside the housing was dirty or did you clean it?

 

[bucket]

How's the injector's spray pattern look? Nice fine mist? Do they drip after you shut the truck off?

 

[johns87]

I did disconnect the battery, but i haven't drove it around any. How long does it normal take to get the computer to learn?

I didn't notice if the IAC area was dirty. I know the whole thing was dirty and I cleaned it up good. It is a new IAC now.

Spray pattern seems to be a nice pattern, and I don't see any dripping.

 

[1987 GMC Jimmy]

I've read this post a million times to see if I could come up with something. Did you say that every time you check the timing after you adjusted it and start the truck up, it'll be slightly different, and you'll adjust it a little to compensate, and it keeps doing this?

 

[johns87]

So today I tried things again and here is the result. I turned the truck on to a really rough, almost missing feel. After a few seconds, the idle increased and it smoothed out. I let it run for about 15 minutes, and it seems to have been running pretty smooth. I turned it off and unplugged the ECM timing wire. Turn it over and it will barely run, feels like it is missing, super low idle. I ran around to the front and turned the distributor clockwise and it smooth out some. Checked the timing and it is a little advanced but now the timing light is only flickering every few times, almost like it isn't getting good power or a good spark signal.

I checked all my plug wires, coil plugs, but everything looks good. My coil clips are in bad shape, so about to put on new pigtails. And now I'm also wondering if maybe me cheap timing light is messed up.

 

[4WDKC]

So today I tried things again and here is the result. I turned the truck on to a really rough, almost missing feel. After a few seconds, the idle increased and it smoothed out. I let it run for about 15 minutes, and it seems to have been running pretty smooth. I turned it off and unplugged the ECM timing wire. Turn it over and it will barely run, feels like it is missing, super low idle. I ran around to the front and turned the distributor clockwise and it smooth out some. Checked the timing and it is a little advanced but now the timing light is only flickering every few times, almost like it isn't getting good power or a good spark signal.

I checked all my plug wires, coil plugs, but everything looks good. My coil clips are in bad shape, so about to put on new pigtails. And now I'm also wondering if maybe me cheap timing light is messed up.

It can take a long time if it even has the capability to figure it out on its own, I replaced one in my s10 years ago because it would die when I came to a stop, it took months for it to work tht out because I didn't have a scanner to communicate with the OBD2. First thing is google the reset procedure, Second I see you listed everythin in the ignition except the coil they werent the strongest when new and 30 yrs later is probably weaker also. I have a Vortec motor coil planned for my truck as they are stronger and needed to jump the large gap the vortec heads use.

 

[TIE_Fightertk06]

Yep, i just thought the same thing as @4WDKC

Coil and distributor.
The HEI module would be a place to start, all the way out to the coil. I use Pertronix flame throwers on all my HEIs.

Check your timing light on another vehicle just to eliminate that as a contributor to diagnosis issues as well.

You said those parts are new, but that really sounds like a spark distribution problem that the computer is trying to compensate for.

Another guess would be deterioration of wires in the ECM path...?