Aaron Bridges

Ok so ive been running lean on both banks for a while my long term Fuel trim on bank to pegs out at idle and drops during drivetime but at idle it goes right to 1.25 short term trims and bank 1 look good all stay close in the negative. Ive replaced 02 sensors, maf sensor, fuel pump had it smoke tested no leaks replaced intake manifold and all gaskets. everything I can think of, did a pi head swap back in april ran great until I took the old intake off to put correct heater tube and coolant nipple in. Im at a complete loss, im about to take it to Pro Dyno in Ft. Mill SC next week if I cant get this fixed myself any suggestions send it my way btw. Fuel pressure is good. no vacuum leaks no intake leaks. everything is as tight as a whistle mods off road x with mils, slp 1's HEADS CAMS AND new intake from 2000 GT

petrock

http://www.obd-codes.com/p0171
http://www.obd-codes.com/p0174

The job of LTFT is to keep STFT as close to zero as possible. If you add the LTFT & STFT for bank 1 together it should be between -10 & +10. Same with bank 2’s numbers. Positive numbers indicate the computer adding more fuel (rich condition), and negative numbers indicate the computer removing fuel (lean condition).

The codes you have indicate that the O2 sensors are detecting too much oxygen in the exhaust compared to the amount of fuel it is pumping into the engine. It knows how much oxygen should be in the system by the MAF sensor. If you have a vacuum leak between the MAF and the cylinders it can cause this problem. If you have an exhaust leak or not enough exhaust pipe after the O2 sensors, it can cause this problem.

If I understand your description correctly, it sounds like the lean condition happens at idle but not while your driving. Correct? If so, then that would point towards a vacuum leak because vacuum pressure is at its highest at idle.

Good luck...

Aaron Bridges

you are correct on your assumption however I had the car smoke tested 2x neither time showed any leaks. wouldn't it have shown if there was a crack in the lines?

petrock

Not always. When doing the smoke test your supposed to wiggle all the fittings, vacuum lines, air intake tubing etc. If there is a crack, doing that should open it up so you can see the smoke come out. As I theorized before, the leak only happens at idle when the vacuum pressure is at its highest. That would suggest that when there is no vacuum pressure that the leak is sealed. It happens… Good luck...

Stevo86

Check to see if your EGR valve is operating properly. If it is stuck open it will present you with a lean condition at idle but not while driving because the computer expects the EGR to be open. Plus there is less unburned oxygen at cruise to recirculate since the engine runs more efficiently in almost any condition other than idle.

Aaron Bridges

checked egr. and cleaned it its functioning properly resmoked all lines again while moving them around, no leaks anywhere any other possible suggestions?>

Stevo86

Was the vehicle ever re-tuned after you swapped on the PI stuff?

Aaron Bridges

no car was never retuned, i never had it tuned because everything i had ever read on the swap said i never needed a tune, that it was just a straight bolt on, a tune would make it better but was not needed

Stevo86

I can't say that's your problem but you most certainly want to have it tuned. You have changed the cams and compression ratio of the engine.

Aaron Bridges

I do not think its my problem i know it will help, do you think its possible i might have a cylinder going down or leaking head gasket or a piston ring going bad that would cause it to run lean, is there another way aside from doing a compression test im tired of putting money into it, im taking it to get tuned monday