TPI running rough...

[Hossbaby50]

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.

 

[jmd]

Wouldn't hurt to have a scanner on it to see what the O2s are reading, see the crosscounts, view the TPS values, etc.

just a thought.

 

[beater74]

maybe idle air control valve

 

[loafer]

Sounds like you might be running too lean close to idle. Has it always done this from the day you installed the system? Or did this just pop up?

Have you checked for vacuum leaks? Maybe between the throttle body and intake?

You may want to check the coolant temp. sensor as well.

 

[87GMCJimmy]

Did you swap out the 3 wire 02 for the 1 wire? If so, it sounds like the o2 sensor could be getting cold when idling causing the lean condition. When I had the problem with mine I thought it was having a problem in closed loop but it was in open loop with cold o2 sensor. Either way I have a scanner if you need to borrow it for a couple days/weeks.

Mike

 

[HarryH3]

Harley, you've got the open/closed loop part bassackwards.

Closed Loop = Feedback to ECM from O2 sensor. This is when there is a continuous feedback loop. The ECM reads the O2 sensor, then adjusts the fuel, then reads the O2 sensor again to test the results. This can only happen when the O2 sensor is hot enough to provide a signal.

Open Loop = No feedback to ECM from O2 sensor. This is when there is no feedback loop. The ECM makes blind assumptions based on table data vs. engine temp, load, etc. So the feedback loop is open or "broken". This happens when the O2 sensor isn't hot enough to provide a signal.

Do you have the park/neutral switch wired in? The symptom sounds like what happens when the engine thinks it's in park or neutral instead of in gear.

 

[Hossbaby50]

I thought I might have gotten those backward but didn't know for sure.

Harry, my truck is wired to run in park only since I don't have the VSS setup hooked up yet.

Mike, I did switch to a 1 wire 02 sensor last fall. It didn't start doing this till more recently. I might have to take you up on that offer in a couple weeks to use the scanner. It kind of makes sense though that the O2 is getting to cold since it has happened more since the weather cooled off and it only happens when the truck has been shut off for a little while or if it sits idling on the trails for awhile. If the motor is up to temp and the motor is pulling a load (in gear and moving) then it will run fine.

I am going to check the TPS reading soon and re-adjust the idle with the IAC disconnected.

Harley

 

[HarryH3]

my truck is wired to run in park only since I don't have the VSS setup hooked up yet.

That can cause some strange stuff to happen, as the computer thinks that the truck is standing still all the time.

 

[Hossbaby50]

It ran fine for 8 months like this though. This problem is a new problem not a problem that has been this way since the install.

Harley