Long term and short term fuel trims intake leak, low idle, improving fuel mileage. Mpg

[afpj]

What does your maf read, in g/s, at idle? How old is the maf? The general consensus seems to be that the maf starts crapping out around 140k-160k miles without throwing codes.

 

[Burban22]

What does your maf read, in g/s, at idle? How old is the maf? The general consensus seems to be that the maf starts crapping out around 140k-160k miles without throwing codes.

MAF says Delphi in silver plaque on the side. Not sure if its original or has been replaced. Do I need to wait until it’s at operating temp or can I give readings during a cold start?

I have cleaned it a few months ago with the special cleaner spray. It looked clean but did it anyway since I was installing new cold air intake.

This burb used to have an oiled filter open box intake but I didn’t see any oil on maf. The filter always seemed like the oil dried up anyway. I went to a dry filter enclosed box intake.

 

[Burban22]

MAP Fluctuating between 7, 8 and 9. FYI I’m at 6900 ft elevation if that matters.

 

[Burban22]

MAF IDLE

MAF 2k rpm

 

[afpj]

I think it's best to take a MAF reading when it's warmed up, but the values for idle that you posted 0.6 3 lb per minute is about 4.8 grams per second. That's just slightly on the low side, especially considering your RPM is 602. My idle typically sits, after warmed up, round 550 to 560. I have a 5.3 flex fuel, stock. Not sure if you have the ability to borrow another MAF that's known to be good and see if your field trims still are that negative at idle.

 

[Burban22]

Update:
I cleaned my oem Delphi MAF with a q-tip soaked in crc maf cleaner. I gently rubbed the Q-tip on the intake side of each wire, and there was still a little fuzz and dirt built-up that I was able to remove since when you just spray the wires, you can only spray from the downflow side, not the upflow / intake side.

My long-term fuel trims are now -9 and -7 during idle and -4 to -8 driving.

When I have more time, I’ll try putting in the stock airbox instead of my cold air intake box maybe that is causing the negative fuel trims?

Recently went on a 400 mile road trip and got 16 - 17 miles per gallon driving 65 which seems really good for a 2003 suburban 5.3 4WD Z71 3:73 with 2” lift.

 

[Burban22]

Sending off all 8 injectiors to this cleaning service. Comes out to about $10 per injector. They don’t give flow rates or anything special but have good reviews and I’ll update if my LTFT improve from the -10 through -3 I’m currently seeing once they are clean and reinstalled.

Pardon Our Interruption...

 

[Fless]

When you get them back, a good bi-directional scanner can perform an injector balance test, along with a fuel pressure gauge.

 

[2006Tahoe2WD]

I'm curious to see if your LTFTs change. I'm running +2-4% at idle and ~+10% on the highway. I'm thinking the injectors are not flowing enough and the "+" values are caused by the ECU trying to get more fuel.

 

[Burban22]

Received my cleaned fuel injectors back with new upper and lower O-rings although I had to replace the lowers with the originals as the O-ring they included were just a little bit too big and I couldn’t get the injector all the way in the intake.

The place I used only charges $9-$10 per injector after shipping so they don’t include flow rates.

My injectors do look much cleaner and they replaced the screens inside the injectors and the lower plastic caps.

After all this, my fuel trims are now taking away even more fuel, -12.5 at idle but -3.5 to -9.5 driving. I’ve only driven it once since resetting the computer as the battery was unhooked for a few days.

Suburban runs the same. Will see if there’s any fuel mileage improvement, but I would assume the injectors were dirty after 170 K miles and 20 years.

 

[Fless]

Did you reset the LTFTs when the injectors were replaced? Those values are learned and could be carried over from the prior situation. Eventually they should get closer to what the STFTs run.

The STFTs show it slightly adding some fuel, well within ideal, so there's that. Those are instantaneous trims, and reset at every ignition cycle.

 

[Burban22]

Did you reset the LTFTs when the injectors were replaced? Those values are learned and could be carried over from the prior situation. Eventually they should get closer to what the STFTs run.

The STFTs show it slightly adding some fuel, well within ideal, so there's that. Those are instantaneous trims, and reset at every ignition cycle.

I don’t have a nice enough scanner to reset LTFT. I disconnect battery for a few days which I thought reset the LTFT? If not hopefully it will get better after 100 miles or so.

 

[Burban22]

I’ve only put on 100 miles since injectors were cleaned and LTFT are still -7 to - 12 at idle but during driving my STFT are now adding fuel occasionally along with the LTFT. This is a change for the good as before injector cleaning it was almost always removing fuel at idle and driving.

I’ll post back my next few hundred mile highway trip if any mpg improvement but I’m doubtful as I could still pull down 16 - 17 at 65 with dirty injectors.

 

[Burban22]

Holy crap that fuel injector cleaning service really helps!

We got 22 miles to the gallon down to Phoenix and back up to mayor / Arcosanti.

15mpg on the climb from Arcosanti to NAZ. Best I could ever get before was 18 - 19 down and 13-14 up.

Fuel trims are still negative at idle but while driving on the interstate 68-70:
STFT -5 to +6
LTFT -7.8 to +6

 

[2006Tahoe2WD]

Received my cleaned fuel injectors back with new upper and lower O-rings although I had to replace the lowers with the originals as the O-ring they included were just a little bit too big and I couldn’t get the injector all the way in the intake.

The place I used only charges $9-$10 per injector after shipping so they don’t include flow rates.

My injectors do look much cleaner and they replaced the screens inside the injectors and the lower plastic caps.

After all this, my fuel trims are now taking away even more fuel, -12.5 at idle but -3.5 to -9.5 driving. I’ve only driven it once since resetting the computer as the battery was unhooked for a few days.

Suburban runs the same. Will see if there’s any fuel mileage improvement, but I would assume the injectors were dirty after 170 K miles and 20 years.


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Good info. Thanks for the report.