Aaron Bridges

Ok Guys So I have had a drivers side lean problem for a while now, Monday I Broke down and took it to get Tuned By Dan @ Pro Dyno In SC, I had already checked for Vacuum Leaks Smoke Tested it 3 times Replaced Intake Manifold, Fuel Pump Fuel Filter, Anything that vould possible throw this code I fixed I have done a PI Swap So I just thought maybe it needs to be tuned, while hooked up on the dyno and he was watching the trims all of the sudden it started running right then about 10 sec later it would start running to **** again pegging out the LTFT To 1.25 He said that has to be a wiring prolem be it that or PCM is bad, theres no other explanation as to how it can kick on and off running good and bad. so does anyone have any Idea as to begin to trace down this possible problem, Start with PCM first or wiring harness, we were guessing its going to be from The Drivers side 02 wiring to somewhere to the PCM? or should i Bite the Bullet and take it to My buddy at the Ford Dealership?

petrock

Is that 1.25 volts? If so, then thats not LTFT (Long Term Fuel Trim). That is the voltage being generated by one of the O2 sensors. They typically generate between .1 & .9 volts. Anything more then 1 volt means you have a short somewhere in that O2 sensors wiring.

LTFT is usually defected as a percentage. If you add the LTFT and the STFT (Short term fuel trim) for a bank together it should be between 10% & -10%. Outside of that range and your running rich (if below -10%) or lean (above 10%). The LTFT numbers aren’t very useful without the corresponding STFT numbers. But 1.25% LTFT is pretty good. Ideally, LTFT & STFT should be floating around 0%.

What was the exact code you got?

Aaron Bridges

no 1.25 percent fuel i shouldve said that

Aaron Bridges

voltage is good on the 02 sensors the ltft and stft on bank one do correspond each other however at idle only the stft and ltft do not on bank 2. for some reason while he had his computer hooked up to it there were mooments when it just started running riught then go bad again.

Aaron Bridges

im throwing p0174 drivers side lean code. we checked for burnt valves there are none cant be anything compression wise cause it would constantly run bad also could rule out jumped timing or anything of that sort because also it would not run good at all

petrock

1.25% LTFT is a good percentage. It isn’t an indication of a lean condition. Its right around where you want it. The job of the LTFT is to keep the STFT around 0%. So if your LTFT is at 1.25% then the STFT must be bouncing somewhere around there.

A lean condition that would trigger a code would have the LTFT in the 20’s or 30’s and the STFT anywhere between 0 & the 20’s or 30’s.

Because it is intermittent it sounds like an electrical or vacuum problem to me. Check out this site for some possible solutions: http://www.obd-codes.com/p0174

Good luck...

Aaron Bridges

i know the ltft and stft is suppossed to off set each other but the stft stays around .95 and 1.0 so i know thats not right its adding 25% more fuel than needed i could prob upload a video of the data log for you to see. as stated i have no vaccum leaks i have smoke tested it 3 times i have double and triple checked everything it has to be electrical

petrock

If the computer was adding 25% more fuel, then the LTFT and/or the STFT would be 25. I think you have your numbers crossed, or the tech who got the numbers for you got them mixed up.

A video of the scanner display would be helpful. Make sure it has the STFT & LTFT %’s for both banks in view.

btw, here is a good video that explains how STFT & LTFT work and how to use it to diagnose problems.

Aaron Bridges

I havent had time to post up a video but im about to, i will say again its intermittent when its running like this, it will sometime run good then bad, my thinking is a bad PCM, possible wiring harness short, maybe the alternator is not running enough amperage???

Aaron Bridges