2002 blazer LTFT 25% STFT 54% ? Running Lean !!HELP PLEASE
 

Hi, i have a 2002 that is running super lean , my LTFT B1 25% and STFT B1 54% at Idle and normal numbers at Bank 2. ..my scan tool also shows P0300 and when i check, it is misfiring on cylinders 1 , 3 and 5 ... when I accelerate to 2500rpm it quickly goes to 0 then starts climbing rapidly to 54% as i hold down the accelerator. I did a fuel pressure test and it is at 55-56 psi on idle. when i open throttle goes up to about 60psi and instantly goes down to 53psi and back to 55 psi so i dont think it is fuel pressure but dont know specs so i could be wrong? the car shakes or vibrates at idle and has a smell and some smoke coming out of the pipe i believe right before the cat next to the o2 bank 2 sensor. Does anybody have an idea what is causing this ? i changed, plugs, wires, cap and rotor... I'm thinking an exhaust leak or manifold gasket leak?? not sure what to think actually !!!Thankhttps://blazerforum.com/forum/images...icon_smile.gif you!

Please put +/- signs on all fuel trims and report both banks.

George

Sorry, Bank 1 LTFT +25% , STFT +54% ......Bank 2 LTFT -9% , STFT -3%...these are at idle ! thanks

You add the LTFT and STFT for a given bank. +79% on bank 1 is crazy high (adding fuel command for a perceived lean condition), never seen this before. Cylinders 1/3/5 are all three on bank one. You have extra air, restricted fuel delivery, bad sensors or a bad PCM.

So when you increase rpms the bank one total fuel trim goes to near zero and then back up to +79?

If you have scanner live data capability look and see if the O2 sensors look normal. They should oscillate between 0.3V ish and 0.8V ish every second or so. What happens if you swap the two upstream O2 sensors?

Does the truck run better initially while the live data shows the system in open loop (not using the O2 sensors yet)?

Have you done a compression test? Have you looked at your vacuum hoses? Have you addressed the lower intake manifold gaskets? How many miles?

George

yes it goes to 0 then quickly rises to LTFT +25% STFT +54% bank 1 ....bank 2 remains normal...o2 sensors operate normal for first 30 minutes then car starts to run rough and sensor 1 bank 1 starts to read .3v to .4v .....sensor 2 bank 1 reads .8v - .9v ... bank 2 sensor 1 fluctuates normally .3v -.8v....
hopefully i will do a compression test today... in open loop the car runs normal for first 30 minutes ...vacuum hoses look ok, have not found cracks or holes in them.. previous owner said he did the intake gaskets 3 years ago but i cant confirm that it is true.. or that it was done correctly.... miles are 190,000....car ran perfect for 3 years since the day i purchased it..

Try swapping the two pre cat sensors to make sure the problem doesn't follow the sensors. That and the compression test and we'll know a lot more.

Are the injectors originals?

George

i will attempt swapping the sensors and doing the compression test today. the spider is original , but i did a pressure test and it gives me a steady 55-56psi with no leak when i turn it off , holds pressure.

Report on the condition of the plugs after the compression test. If the injectors are the problem it would be plugged/insufficient delivery resulting in a lean condition resulting in an attempt for additional fuel delivery hence the positive fuel trim.

i will try to upload some pics of the plugs and tests results today

Thank you for the help!!!!! Turns out my bank 1 sensor 1 was lying to the pcm. Put in a new sensor and the truck is now running smooth!!!