I have just completed an LS Swap (2001 5.3) into my 1981 El Camino. When in Open Loop at first startup the car runs great and drives like a champ. As soon as it hits closed loop it absolutely falls on its face. Immediately in the Short Term Fuel Trims the passenger side (Bank 2) shoots up to +51% almost instantly. While the driver side (Bank 1) goes down to -31% in the same speed as Bank 2. I will separate my multiple concerns below in hopefully an easy way to read and answer to.

I put new 02 sensors in it on the upstream, they are AC Delco. The rears are not in the exhaust but still plugged in. They should not be able to effect the performance at all. When taking out the old ones the passenger side was dark black while the driver was just a little black which is because the car wants +51% more fuel on the passenger side for some reason.

Full exhaust system with hi flow cats and mufflers, problem occurs with and without exhaust on the car.

My theory right now is that it is something wrong with the tune in the computer. If there was a major vacuum leak or non firing sparkplug/fuel injector, to my understanding the car should run bad in open loop aswell but in open loop it runs completely fine. Please correct me if i am wrong on this and if I should be checkin all the plugs and injectors.

NO CODES AT ALL

The engine, transmission and PCM were taken from one donor truck that ran good in open and closed loop. The computer was sent out to get the wiring harness re-done and removed a lot of the unnecessary things that connecter to the car itself. Now it acts as a standalone computer. I did give the guy some info like tire size and rear end ratio so he could adjust the tune. Unfortunately he does not do the harnesses anymore and was hard to reach even when he did. I believe there is a chance something could have been messed up while he was in there and want other peoples opinions about it.

I know a few guys around that could possibly help me look at the tune but I wanted to share this here and get some other eyes on it.

Let me know if there is any info I am missing that is crucial to diagnose this.

 

Check your wiring. If the LTFT are max positive and negative, you may have the 02 sensors swapped drivers to passenger.

 

I wonder if your front and rear sensors are wired correctly in your new harness?

I would unplug your rear sensors and make sure you get the proper codes for that "problem," which would partially confirm the wiring for the sensors. (i.e. If you get a code back for one front sensor and one back sensor, that would confirm a wiring problem.)

 

From my 24 years experience with GM EFI, if the front and rears are swapped, the readings would stay at about 450mV and not cause one bank to swing positive and the other negative.

 

Shouldn't make a difference given they are the same sensor for both sides and same distance down stream.

I'd check the wiring to make sure the wires are in the correct pins for the signal wires to the PCM.

 

Very recently around here, I had the similar symptoms and was advised by member "Gametech" that he thought my O2 sensor cables were swapped. Sure enough, mine were wrong - I installed them correctly and instantly had a perfectly operating rebuilt LM7 engine with a PSI Conversions harness.

Rick

 

Merv, not what I have experienced. If the pcm is seeing lean on driver but reporting it electrically on pass side, any deviation will be exasperated and continue on the wrong bank/side till it is max out. Conversely on pass/opposite side its got nothing to do with the sensor part number and in most cases how far down stream, providing the reported signal is measured pre-catalyst.

 

I was thinking that only one side could be switched front to rear.

 

thats not what im saying.


Im saying the driver side wiring is connected to the passenger side sensor and the passenger wiring is connected to the driver sensor.

 

Yea, I could see that now. That makes sense and where I would look. Long day yesterday I wasn't tracking on it.