87 Suburban, no RPM signal, won't idle

[Bob87Burb]

It's always something....

A couple months back, when diagnosing a surging problem I just can't seem to nail down, I swapped a known good distributor in, and it made no difference. I put my original distributor back in, set the timing, and called it a day. Upon firing it up, the truck would not idle at all. It would start, run for a few seconds, and then die.

I've installed a new fuel filter, IAC, checked the fuel pressure, checked and re-checked the timing, TPS adjustment, Temp Sending Unit, MAP sensor, EGR system and vaccum, and I'm at a loss. I've turned the idle up so it won't stall when in Park, but I need to keep my foot on the gas when in Drive to keep it running at a red light.

Other things of note:

-The truck will stay running when the timing connector (sorry, forgot the technical term) is disconnected, but obviously it's a dog driving it like that, due to no timing advance. When I hook the connector back up, it returns to stalling as described above.

-I attempted to check the idle speed using the tach lead off the coil, and it doesn't seem to be working correctly. On my meter, it reads 120 RPM, and when I blip the throttle open, the value goes down instead of up. I checked the meter on another car with no known issues, and it worked fine on that one.

-None of this ever happened before I swapped distributors.

1987 Burb, 350 TBI, engine and trans are bone stock.

Thanks in advance for any help!

 

[dyeager535]

Post by "thegreatj"

When I scanned my setup, my ECM was not showing it was seeing the engine crank, so my problem very well may be the module.

Apparently on the ignition module there is some sort of failure indicator...a dot or something that pops up when something fails. I've never seen pictures of this, but coming from who said it, I believe it. I just wouldn't trust an electrical component 100% of the time to tell me it has failed, but it's worth a look I guess.

With the bypass disconnected "fixing" the problem, I would suspect that the module is faulty, although I'm not sure, does TBI use a seperate spark module like my TPI does?

thirdgen.org is probably a good place to search for answers to your problem though, or learn more about why it may be doing what it is.

 

[Bob87Burb]

OK, I'll try thirdgen.org out. I forgot to mention, I replaced the module as well. I'm pretty sure the TBI setup uses some sort of ESC and/or EST. Just need to find out what the heck does what.

After messing with it some more tonight, I'm starting to think that while I was swapping distributors, I may have damaged a wire or something.

Thanks for the response, this is really driving me nuts!

 

[dyeager535]

Only thing I can suggest is getting/finding someone that has a service manual.

Thirdgen might have somewhere in all the archives the troubleshooting flow chart, but if all you get is a list of things that COULD be bad, it's not really going to help you.

Most, if not all of the troubleshooting flowcharts help you test both the components AND the wiring, and that should be pretty similar between the car and truck TBI setups.