hello there! I have a 99 Chevy Silverado, with 335,000 miles on it. The other day, my truck threw a check engine code for the first time. PO 171, and 174, saying both banks were too lean. At the time, we had been below 0 for 5 days. STFT Numbers have read perfectly every since I got my scan tool. Before we warmed above freezing, LTFT was running between 20-25% at all rpms, then the check engine code went away after about 2 days. Now, 5 days later, both STFT and LTFT are normal at idle and all rpms (not driving though), and LTFT only goes above 6% when I press down the accelerator (while driving) but if I let go of the gas, even at 2000 rpms and 75 mph, it drops down to below 6%. I have no idea what is going on. Had some ideas at first but the data is being to crazy on this.
MAF is running interesting, 4-5g/s at idle, and up to 50g/s while at 1500rpms driving. And O2 sensors seem to be running fine too
no really cold weather can do naughty things the electronic and computer systems but if it does have problems running even when it warms up a lot of times a week fuel pump will do that it doesn't pump enough fuel which makes the engine run lean
Ok Scotty, thank you! I’ll have to have my fuel pump tested but other than those numbers, the truck runs great. Doesn’t bog down or lose acceleration or anything so another reason why I’m at a loss
Yeah listen to Scotty. And I would check for vacuum leaks too.
