Hi All,
I am having a strange problem with the Computer Control system on my 350 TPI powered 82 Firebird. First I will give you all some history.

I purchased the car new in Jan, 1982. In 1998 I replace the original LG4 V8 with 350TPI engine. Now I’m not racing but wanted to improve the derivability, durability, and fuel economy of my Firebird. I basically succeed in the conversion. I order the complete TPI system from Fuel Injection Specialties in San Antonio, TX. The TPI came with a custom programmed ECM that was set up for my 3-speed auto and 2.73 rear end. I am using the GM Goodwrench 5.7 Liter motor P/N 10067353. At that time I installed a 2 ˝” in/out high flow converter, and 170 degree thermostat. In 1999 I moved to Wake County, and added the Air-injection back onto the engine. The TPI 350 passed state emissions tests with absolutely no problems from 1999 though 2002. In 2000 I installed an SLP cat-back system and a MSD 6A ignition system. The Firebird ran perfect, got great fuel-economy 25MPG on highway, 18 in town and was a blast to drive.

In November 2002 a woman driving a mini-van, ran a stop sign and hit the front right corner of my bird. The Bird stayed in the body shop till October of last year. The bodywork is great and the suspension is great, have absolutely no problems with handling.

Now the hard part, she is failing emission testing. I have replaced MAF, O2, verified Canister operation, EGR, tuned it up with new plugs, cap rotor, wires etc. Please note the MAF was toast when the car was return to me. I have been able to connect my laptop to the ALDL connector and scan the ECM. The temperature sensor read out agrees with my dash gauge. The problem is that the ECM is staying in OPEN-LOOP mode at idle. I can rev the car up and after a few minutes the ECM will go into the CLOSED LOOP mode. But as soon as it drops back to idle, the ECM returns to OPEN LOOP mode. When driving the ECM will go into Closed-Loop and switch back to Open Loop at stop-lights.

The only changes to the engine setup that been made is now I have a SLP Y-pipe and 3” in/out High Flow converter.

Please note that when the body shop had the car that they was doing welding while the ECM was still mounted in the car and the battery connected.

I have disconnected the O2 sensor at idle and connected a voltmeter to it and the voltage is varying. The scan of ECM indicates the the O2 voltage is varing from about 30? to about 45? MV.
The car does not smoke, seems like it running OK, plenty of power, “like not it was”! Exhaust smell is a little OFF, seems like its running rich.

The high voltage on the TPS is about 4.13 VDC, should it be able to reach 4.85VDC.

So is it possible that the ECM is now defective?

Due to SLP Y-pipe, do I need to switch over to a heated O2 sensor? Yes I am still using stock exhaust manifolds.

Has anyone of you purchased an ECM from Advance Auto?

Thanks for your help.

 

maybe you need to get a heated 02 sensor do to the fact the sensor maybe moved up stream with the new y pipe. I have heard of this before.

 

I'm not an expert about this, but I know a little. what you have to worry about is what is telling it to go to closed-loop when the RPM goes up? one of the biggest factors os temperature, so just make double sure that the computer is recieving the right input for that.
~Erik~

 

Thanks guys, but this is really old post.

But to update you all. In Sep of 2004, the ECM went dead and the car would crank but not start. To cut directly to the end of story, I replaced the ECM and the car started and set O2 Sensor code. I replaced the O2 sensor and the code was set again. I check the wiring with an ohm meter and found a open ground to the O2 Sensor. I found the open circuirt and repaired the wiring. No problems sense, no more rich running. The car runs great now.

PS. I in process of replaceing the transmission with an 4L60e "computer control". Please go to the transmission board and check my thread. The new 4l60e goes in the day after Christmas.