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Fuel trim

  • danshere
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3 years 7 months ago - 3 years 7 months ago #54467 by danshere
Fuel trim was created by danshere
Hey guys I have a 2006 scion tc with a p0171 code for a lean condition but the thing is my stft is between -11 and increases up to -18 at idle but my Ltft is at +8 .when I raise the rpm short term moves closer to 0 as does long term here are pics of freeze frame data and live data
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Last edit: 3 years 7 months ago by danshere. Reason: added attachments

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3 years 7 months ago #54481 by danshere
Replied by danshere on topic Fuel trim
I did clean it but that didn't change anything thanks for the reply by the way

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3 years 7 months ago #54482 by danshere
Replied by danshere on topic Fuel trim
I did try that cleaned it and still no change and I'm not getting any crazy number from it either thank you for the reply by the way

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3 years 7 months ago - 3 years 7 months ago #54488 by Tyler
Replied by Tyler on topic Fuel trim
It sounds to me like the Short Term is countering the Long Term, possibly over a fault that didn't happen to be present while you were looking at the fuel trims.

Have you had a look at the Freeze Frame associated with the P0171? When the lean condition was present will help you determine what was causing it.
Last edit: 3 years 7 months ago by Tyler. Reason: herp derp

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3 years 7 months ago #54495 by danshere
Replied by danshere on topic Fuel trim
thanks for the response I have checked it and took pictures of both freeze frame and live data at idle will attach them now
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3 years 7 months ago #54498 by Tyler
Replied by Tyler on topic Fuel trim

thanks for the response I have checked it and took pictures of both freeze frame and live data at idle will attach them now


Got 'em, thanks. B) The Freeze Frame really stood out to me:



Nearly 60% correction at 43 MPH? :blink: This definitely suggests an under load, fuel delivery issue. If you go for a test drive with the scan tool installed and watching data, can you reproduce this condition?

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3 years 7 months ago #54499 by danshere
Replied by danshere on topic Fuel trim
Yes I can and another thing is when I stop and then start again it stumbles or if I'm at idle and do a quick push on the gas it sounds like its gonna die before it actually revs up almost sounds like it sucks in air but I smoke tested and had no leaks I was thinking fuel delivery to but wouldn't it be a positive stft not a negative thanks for your help

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3 years 7 months ago - 3 years 7 months ago #54502 by VegasJAK
Replied by VegasJAK on topic Fuel trim

Nearly 60% correction at 43 MPH? :blink: This definitely suggests an under load, fuel delivery issue.
As Tyler says, fuel delivery problem. At 43mph you're running a total 60% total positive trims. The anomaly of neg STFT at idle could be the intermittent failure of the fuel pump or regulator as examples or the ecm attempting to make a correction. Do some fuel pressure tests. Snap throttle test will show a lot. Any decrease in pressure is what to look for. Is it taking longer cranking time to start.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
Last edit: 3 years 7 months ago by VegasJAK.

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3 years 7 months ago #54646 by danshere
Replied by danshere on topic Fuel trim
Sorry been working but got time to get a pressure gage on it so here is a update ,ar idle the gage reads 50 psi and is steady but when ishut off the car it drops to 40 then very slowly will bleed off ,but from what I've read its within a reasonable amount of time but i don't know if the instant drop of 10 psi when i turn of the ignition is normal.I havent done the snap throttle test yet and again thank you for yours and everyone's help

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3 years 7 months ago #54648 by VegasJAK
Replied by VegasJAK on topic Fuel trim
Snap throttle test will tell alot. Snap throttle to wot watch fuel pressure. Should not see a drop in pressure of more than a pound or two. Preferably no drop.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
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3 years 7 months ago #54651 by danshere
Replied by danshere on topic Fuel trim
Hey bud did the snap throttle test and it dropped maybe a 1/2 psi it is hard to even see it drop thats how little it moved and you had asked if I could recreate the freeze frame data and its nearly identical

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3 years 7 months ago #54652 by danshere
Replied by danshere on topic Fuel trim
you had me check my calculated load at wide openthrottle and heres what I got at idle its 16.9 at 3500 rpm it goes to 13.3 and goes from closed loop to open loop what does that mean

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3 years 7 months ago #54662 by danshere
Replied by danshere on topic Fuel trim
I'm sorry I'm I'm a beginner on somethings,when you say "drive at wide open throttle" , should I literally drive it at wot because the previous results were just reving the vehicle to 4000rpm while in park which were at idle 16.9% and dropped to 13.3 at between 3500 and 4000 and at that point is when it goes out of closed loop and in to open do you want me to redo the wot test but actually put tires to the pavement and give you the readings then

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3 years 7 months ago #54681 by danshere
Replied by danshere on topic Fuel trim
Ok did the wot test while driving and the highest the calculated load would get is 44.3% and kept going into open loop of and on while getting to top speed

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3 years 7 months ago #54702 by danshere
Replied by danshere on topic Fuel trim
I did clean the maf already before the tests and I don't know if the 10 psi drop is normal but the rate that it does drop after the initial 10 psi seems to be consistent with what I read but I haven't read anywhere that the drop of 10 psi at shutoff was normal is that abnormal for that to happen with any ather vehicles

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3 years 7 months ago - 3 years 7 months ago #54706 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Fuel trim
Looks like the volume of fuel flow reaching the engine when the engine is under load rather than low pump pressure -- try looking for a damaged crushed fuel pipe or blocked fuel filter or it could be an issue inside the tank
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Last edit: 3 years 7 months ago by Andy.MacFadyen.

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3 years 7 months ago #54707 by VegasJAK
Replied by VegasJAK on topic Fuel trim
Andy, could it be a failed or failing check valve? 10lb pressure loss on shut down then steady loss there after?

Walter: I trying to make myself smarter.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does

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3 years 6 months ago - 3 years 6 months ago #55507 by kovalmax
Replied by kovalmax on topic Fuel trim

Looks like the volume of fuel flow reaching the engine when the engine is under load rather than low pump pressure -- try looking for a damaged crushed fuel pipe or blocked fuel filter or it could be an issue inside the tank

By the way, I agree with the above recommendations. I had a similar problem on my 5.9 Cummins. I was using a poor quality fuel filter and it quickly got clogged, which caused the problem. My mechanic installed me a and the problem was solved. :) Try cleaning it or installing a new one.
Last edit: 3 years 6 months ago by Noah.

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3 years 3 months ago #56759 by Mariowinax1
Replied by Mariowinax1 on topic Fuel trim
Should you drive it to make the wide throttle test or can put the car to part to test it?

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3 years 3 months ago #56760 by Mariowinax1
Replied by Mariowinax1 on topic Fuel trim
Did you solve it friend?
If yes what was the solution?

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