Fuel trim diagnostics

[nonickatall]

If we all talk about the fuel pressure in idle, the fuel pressure should be lower in idle than in throttle.

Therefore a Vakuum hose is at the fuel pressure regulator. If there's a high vacuum, it lowers the pressure.

The background is: In idle, on a closed throttle, the vacuum is much higher in the intake system then on rpm with open throttle.

But the amount of fuel is calculated by the ECU on the data of the mass air sensor and is regulated by the opening time of the injectors at a defined fuel pressure.

If you have a higher vacuum at idle, then it sucks, so to speak, the fuel out of the injectors and the amount of injected fuel is higher, than it should.

That is the reason, why they lower the fuel pressure in idle.

 

[strutaeng]

It sure seems like symptoms of a vacuum leak given the fuel trims at idle and a higher RPM.

So it's only on bank 1, correct? Things like MAF, MAP, EVAP leak into intake (that one would actually cause a rich condition) would affect both banks equally. Same with fuel delivery issues.

A misreporting O2 sensor could also cause a perceived lean or rich condition, but doesn't sound like the case here.

Is the CEL triggered? I'm assuming it was running good at some point?

 

[afpj]

It's both banks actually. They read the same on the fuel trims. That's why I was leaning away against the intake gasket leak. But so far my diagnostics haven't really shown anything. There are no codes, I have a scanner capable of reading ABS, SRS and body codes in addition to the standard p codes. Even though the MAF seems to read okay, ie reads about 5.4 g/s at idle and then goes up from there with throttle. Runs good, plenty of power, very slight rough idle with AC on. With AC off it's extremely smooth. Although the MAF reads about 5.0 or 4.9 with the AC off, 5.4 g/s with AC on, think that's normal?. Apologize for the rambling, thinking out loud..

 

[George B]

What is the fuel pressure?

 

[strutaeng]

It's both banks actually. They read the same on the fuel trims. That's why I was leaning away against the intake gasket leak. But so far my diagnostics haven't really shown anything. There are no codes, I have a scanner capable of reading ABS, SRS and body codes in addition to the standard p codes. Even though the MAF seems to read okay, ie reads about 5.4 g/s at idle and then goes up from there with throttle. Runs good, plenty of power, very slight rough idle with AC on. With AC off it's extremely smooth. Although the MAF reads about 5.0 or 4.9 with the AC off, 5.4 g/s with AC on, think that's normal?. Apologize for the rambling, thinking out loud..

Yes, MAF values seem okay.

 

[afpj]

What is the fuel pressure?

oh heck, I knew I forgot something. He had the fuel pump changed maybe 3000 miles ago, fuel filter about 2000 miles before that. Said Ac delco for both. Haven’t put a gauge on it even though I thought about it, after being reminded here, but then the thought fell out of my brain. It’s sucks getting old.

 

[George B]

oh heck, I knew I forgot something. He had the fuel pump changed maybe 3000 miles ago, fuel filter about 2000 miles before that. Said Ac delco for both. Haven’t put a gauge on it even though I thought about it, after being reminded here, but then the thought fell out of my brain. It’s sucks getting old.

Was the pump installed in an attempt to fix this issue?

 

[BG1988]

After that I'd say reset the LTFTs; they've been learned and may need to be re-learned over a bit of time, and monitored.

sticky closed fuel injectors

https://royalpurpledirect.com/max-clean-fuel-system-cleaner-and-stabilizer/

if the LTFT is that high i would keep an eye on the oil for fuel contamination and a P0420 &/or P0430 code soon.... been there done that...

mine was 15+ to 17+, ended up getting fuel contamination into the engine oil (smelled of gas)

currently is at +3 to +5 LTFT..after using the royalpurple 2x bottles at two different fill ups. i have not checked it with the K&N filter

 

[Tonyrodz]

sticky closed fuel injectors

https://royalpurpledirect.com/max-clean-fuel-system-cleaner-and-stabilizer/

if the LTFT is that high i would keep an eye on the oil for fuel contamination and a P0420 &/or P0430 code soon.... been there done that...

mine was 15+ to 17+, ended up getting fuel contamination into the engine oil (smelled of gas)

currently is at +3 to +5 LTFT..after using the royalpurple 2x bottles at two different fill ups. i have not checked it with the K&N filter

Interesting about the fuel contamination in the oil.

 

[strutaeng]

Yep, double check fuel pressure. Fuel delivery can definitely cause lean condition on both banks (either pump or FPR.)

Even new parts fail or are defective out of the box. You can't assume something is good because it was replaced.