Strange fuel trims
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From: Hobart, IN
Strange fuel trims
I think we have finally found our vacuum leak, and now have long term fuel trims at 4%, and short term fuel trims at 0 to -.8% at idle. The problem comes in, when we accelerate down the road, and our long term fuel trims race to 19.5%, and our short term trims are at 15%. Also, after a long cruise(about 70 miles) we are getting lean faults on both banks. So it would have to be something that would effect the whole system. If it was a vacuum leak, I would be seeing it at idle now, I think.
The injectors have been professionally cleaned twice, with a Motorvac system, and a B and G pressure clean system........Any ideas?.......fuel pump?.....upstream 02 sensors?........Thanks in advance......Mike
The injectors have been professionally cleaned twice, with a Motorvac system, and a B and G pressure clean system........Any ideas?.......fuel pump?.....upstream 02 sensors?........Thanks in advance......Mike
Here's something I just posted in another thread about P0171/P0174 codes, maybe be helpful? The list of suspected culprits I mean.
Friend of mine has a supercharged F150 Lightning, he just picked it up cheap a few weeks back because the check engine light was on and the owner was clueless about fixing it.
Yep it had P0171 and P0174 along with the CEL. Fuel trims were off the charts at +25% on both banks LTFT and the STFT's were also very high at idle.
He spent hours searching for a vacuum leak, and in the end, he couldn't find one.
I hooked up my IDS to see if it might give some clues, and it gave a list of likely culprits.
No fuel pressure sensor in this truck so we put in a new fuel filter just to rule it out, the old one was so choked up I could not blow through it, and a dirty brown sludge came out of it.
Seemed to make some improvement, but the trims were still off the chart.
So he chucked a bottle of injector cleaner in the tank and filled up with a high-ethanol content fuel. Drove it around for a couple of days and it slowly got better & better, it sounded better, it drove better, and after clearing the codes, they haven't come back since.
So it was blocked up injectors and fuel filter that was causing the P0171/P0174, not a vacuum leak.
Not saying this is your problem, just sharing some recent experiences.
Yep it had P0171 and P0174 along with the CEL. Fuel trims were off the charts at +25% on both banks LTFT and the STFT's were also very high at idle.
He spent hours searching for a vacuum leak, and in the end, he couldn't find one.
I hooked up my IDS to see if it might give some clues, and it gave a list of likely culprits.
No fuel pressure sensor in this truck so we put in a new fuel filter just to rule it out, the old one was so choked up I could not blow through it, and a dirty brown sludge came out of it.
Seemed to make some improvement, but the trims were still off the chart.
So he chucked a bottle of injector cleaner in the tank and filled up with a high-ethanol content fuel. Drove it around for a couple of days and it slowly got better & better, it sounded better, it drove better, and after clearing the codes, they haven't come back since.
So it was blocked up injectors and fuel filter that was causing the P0171/P0174, not a vacuum leak.
Not saying this is your problem, just sharing some recent experiences.
Thread Starter
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Veteran Member
Joined: Jan 2015
Posts: 1,231
Likes: 237
From: Hobart, IN
Today we observed bubbles in the fuel stream, even though the pressures were close to specs. Maybe my 102,000 mile fuel pump is starting to cavitate. I am thinking these may be my cause for the lean burn codes. Any ideas? I am kind of counting on your feedback, because it is over $600 to have the fuel pump replaced.......Thanks......Mike
Last edited by mrplow58; Oct 17, 2016 at 08:20 PM.
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