for the last week or so ive been having this problem in my TPI Vette. as soon as the coolant temp hits mid 150s, the car will bog for a few seconds (like the fuel lines suddely became kinked), then it will rev fine, then bog again, then rev fine, etc. it does this from 157* until i shut the car off. the fuel pump is new (2 months old MAX) and i dont think the problem is with that (ive checked for FP and everything is fine). i also had a spare ignition module lying around and threw that in... car still had the same problem.

about a month ago the car would do this to me at the track, but only when i launched. it would bog, then pick up and rocket down the track

im thinking ECM failure possibly, and have a reman unit from GM ready to go in, unless you guys have any insight to add. any suggestions?

 

well i just got back from swapping a GM rebuilt ECM into the car. this is very confusing. put the new ECM in the car. car cranks but wont start. tried a few times, but same result. took out the new ECM, put the old one back in, car starts.

one thing i did notice was that the 2 ECMs had different part #s...

OLD ECM - 16198259
NEW ECM - 88999194

i was told the new ECM may be an "updated" part. so would this mean the PROM from my old ECM will not work with the new "updated" ECM? my PROM has the following #s on it: ARAP 1613 4193

 

Your old prom should work in the new ecm. Where did you get the ecm? That part number looks strange.

 

i work at an independant reapir shop and ordered it through the local chevy dealership (so i can get it at cost). apparently they somehow looked up an ECM for the wrong car. im going to give them my old part# tomorrow and send the unknown ECM back

 

I would check the resistance on your fuel injectors. They are supposed to be between 11-14ohms resistance. I had the EXACT same problem on my TPI. It would run great when you first started it or was cold. But after it warmed up, it would idle bad and bog under accel for a min, then pick up and run like a beast. Turns out, the injectors get heat soaked from the intake manifold, and over time it wears out the insulators inside the injectors, causing the resistance to be greater or lower. This in turn causes irregular spray patterns.

OR, Ive learned that dirty injectors can cause the same problems with driveability and acceleration. Really dirty injectors can actually cause the resistance readings to change. Id say check the resistance(motor warm and cold). If they are out of spec, get some concentrated injector cleaner(screws onto fuel rail) and run it through and see what that does. If they are still out of spec, Id replace them.


Good luck

 

Where can you get that?

Thanks,

Matt

 

ive heard that injector cleaner will short out the Multec brand injectors (which are found on my 89'). its safe for the earlier Bosch injectors, but the only fix for the Multecs is to replace them.

as for replacement injectors... are the Accel ones any good? theyre pretty cheap at about $225 for a set of 8.

 

I didnt know that about the Multec's. Probably not a good idea then. As for replacements, Id go with the $99 slp 25lb hr injectors and have somebody(or do it yourself) make a chip that has the injector constant changed from 22 to 25lb hr. Its that simple....and a LOT cheaper than the accel's. Good luck....

 

Check the Pick Up coil....Mine acted similar when it started to go bad..... Mine would really have problems on the top end.... YET when Cold the car ran perfect...

 

Check the Pick Up coil....Mine acted similar when it started to go bad..... Mine would really have problems on the top end.... YET when Cold the car ran perfect...

 

did you ever find out what was wrong?

 

Nope, it doesnt do it as often or as bd lately though. I'm gonna redo the entire ignition system by the end of summer. I am thinking its the MAF sensor though. My exhaust is pretty busted up right after the Cat so I can smell the exhaust. When it does it, sometimes it smells rich, other times lean. I checked the fuel injectors, not a single one was leaking. I added in the cold start injector and ran it to a momentary switch. When it bogs sometimes I hit the switch to add in fuel and it stops the bog, other times it makes the bog worse. So that pretty much convinces me that it is a fuel problem. MAF is my best guess.