I am having a problem with my TPI running rough when it is in closed loop mode (while cool). I can fire the truck up in the mornings and drive it ok and it runs pretty well and once the open loop kicks in everything is fine. If I let the truck cool off after driving it like I go into the store or something and it cools below the 185* (or whatever) for open loops it runs poorly when I start it up and try and drive.

It runs rough and the idle jumps all around from 600-1000 and back and forth. The motor tries to die then the computer catches it and kicks the RPM up and then it goes down again and so forth. In gear it acts all surgie and this is very bad when you are trying to rock crawl in technical areas. Once the truck heats up and hits open loop it is fine again and everything runs normal.

I need to get this problem fixed because I am having problems offroading it cause when I am waiting in line for an obsticle out rock crawling my truck will kick into closed loop mode and run like crap until I heat the motor back up again.

WTF is wrong? I am kind of thinking TPS input might be screwy but I don't know. It trips no codes in the computer at all.............

Harley

P.S. 1988 MAF TPI off a Firebird no VSS (running in Park mode) on a stockish 350. It was swapped into my 85 K5 Blazer about 1 year ago that I rock crawl and drive daily.

 

Check your TPS range but to be honest you might want to try to reset minimum air. You obviously have a scanner if you know when the ECM is toggling between open and closed loop. What are your IAC counts???? Did you use factory manifolds or is it an aftermarket header/exhaust system??? If so where is the O2 bung and is it a heated O2 sensor?

Do a search for the proper minimum air adjustment and "Vader".

 

Actually I don't have a scanner. I just watch the temp gauge and when it is at 150* it runs like crap and once it hits 185* (or whatever degree kicks the system into open loop) it runs fine. Low temp it runs bad and normal operating them it runs fine.

Thank
Harley

 

Hmmm, sounds like your terminology is backwards. Open loop is what your car runs in cold, until it is warmed up enough that the sensors are in range. Closed loop is what your car runs in warm, taking feedback from sensors and applying control. Temperature alone is not the only criterion for triggering closed loop -- the O2 sensor must start emitting a varying voltage, coolant temps must be above 160, etc. Not having your park/neutral switch hooked up properly may be a contributing factor to your problem. I have a TPI swapped onto a 1969 327, and I use a toggle switch to the park/neutral wires so the computer knows when I'm not in park/neutral.