Question on fuel trim

[Donald]

The long term bank 1 fuel trim on my Jeep (at idle) was 21 and on bank 2 is 23. How close should they be? Is the ECM doing this to compensate for something else?

I am much more knowledgeable about power trim on my Mercruiser than fuel trim on my Jeep.

 

[gathermewool]

I only have my old STI to reference (which had a wide-band AFR sensor,) but +/- 4% was my personal threshold for pain. When it started creeping much past that, it was due to a torn turbo inlet hose. I had it fixed under warranty and my long-term fuel trim dropped in half and stopped fluctuating from log set to log set.

I don't know any other application, but if I saw what you're seeing in my old Subie, I'd be very concerned. It's basically telling you that your MAF sensor (these are MAF-based, not MAP-based, right?) is reading so far off, that the AFR sensor is telling the ECU to add a substantial amount of fuel to compensate.

 

[Roadkingnc]

You are running very lean, long fuel trim is usually in single digits and more often than not close to zero.
I would look for a vacuum leak or a biased sensor. Unmetered air leak also if it has a mass airflow sensor.

 

[Trav]

As others have posted its adding fuel like crazy to compensate for an air leak, bad MAF,etc.
What CEL codes does it have?
Get this fixed ASAP and change the oil, it could be \diluted. Has the oil level crept up?

 

[Donald]

I tried it again and I think I forgot that the numbers were a -21 and -23. After driving they were -16 and -19. Old eyes, old memory.

 

[gathermewool]

Also of note, is that the ECU will only add or subtract so much fueling before it's beyond the ECU's capacity to effectively control the AFR. I think that number was something like +/- 25% for Subies.

 

[vssjim]

Fuel trims are always once they settle down from accelerating or just at idle should be plus or minus 10%. you are very lean at idle for the numbers to be that high.

 

[Trav]

Originally Posted By: Donald
I tried it again and I think I forgot that the numbers were a -21 and -23. After driving they were -16 and -19. Old eyes, old memory.

So its subtracting fuel. Any codes stored?

 

[Donald]

Originally Posted By: Trav
Originally Posted By: Donald
I tried it again and I think I forgot that the numbers were a -21 and -23. After driving they were -16 and -19. Old eyes, old memory.

So its subtracting fuel. Any codes stored?


I had a P0456 but cleared it and it has not come back.

 

[Donald]

Originally Posted By: Trav
Originally Posted By: Donald
I tried it again and I think I forgot that the numbers were a -21 and -23. After driving they were -16 and -19. Old eyes, old memory.

So its subtracting fuel. Any codes stored?


These are the injectors I got from Trav.

 

[Trav]

Yes they are guaranteed. I don’t think they are the issue especially on both banks, one maybe but two at the same time on different banks is highly unlikely

Look at the fuel pressure regulator,if its vacuum operated pull the vacuum line and see if there is any fuel there at the hose. If so its defective, if not do a pressure test.
Check the MAP sensor.

Edit: I just looked it does have a vacuum hose.

 

[rslifkin]

FWIW, there's no MAF sensor on those Jeeps and the fuel pressure regulator is on the pump in the tank, there's no regulator on the fuel rail.

 

[Donald]

Originally Posted By: rslifkin
FWIW, there's no MAF sensor on those Jeeps and the fuel pressure regulator is on the pump in the tank, there's no regulator on the fuel rail.


RockAuto does list a Fuel Injection Pressure Regulator for that engine in 2001.

 

[Trav]

It has a MAP sensor also.

 

[gathermewool]

Are the injectors of a different flow rate or characteristic than OEM? If so, then there you go...

 

[Trav]

Same flow rate and current draw. They have been in the vehicle a while.
This engine uses 2 upstream O2 sensors 1 for 1-3 and one for 4-6 so the issue has to be something common to both banks.

 

[Vikas]

Trav already suggested the FPR or the vacuum hose connected to it. That is the most likely cause of engine running rich on both banks. FPR controls the fuel pressure down and if FPR is broken or vacuum hose disconnected, the pressure in the rail will be higher than the specified one which will make car run rich. Concentrate on that aspect.

 

[Clevy]

Jeeps use a speed density type injection system. So no mass air sensor.

 

[linksep]

So your LTFT is Plus 20-something or Minus 20-something? Your first post indicates positive, your second post indicates negative... If your LTFT is positive replace the primary (pre-cat) O2 sensor(s) and see what it does after 100 miles normal use.

 

[Vikas]

sorry but the objective here is to diagnosis here and not do blind parts swapping. tell him how he can actually test the O2 sensor. OP has live data scanner.