Very high LTFTs, no codes

[tomasidris]

So my M3 has had pretty high long term fuel trims ever since I got the car recently, but has gotten significantly worse as of recent. It used to be around +5-8% in both banks, varying by a couple percent between the two, but now reads +18% in bank one and +15% in bank two. I had my injectors rebuilt and flow tested less than 4k miles ago and replaced the fuel filter at the same time. The car has no codes or lights, not even on inpa (at least relating to the engine). Cant find any evidence of any vacuum leaks too. Very rarely and roandomly my car won’t start on the first crank so I suppose that leaves me with the fuel pump, however the previous owner replaced it less than 50k miles ago and I dont want to replace a $400+ part if i dont have to. Any methods of testing to see if the fuel pump is bad? Thanks!

[sapote]

So my M3 has had pretty high long term fuel trims ever since I got the car recently, but has gotten significantly worse as of recent. It used to be around +5-8% in both banks, varying by a couple percent between the two, but now reads +18% in bank one and +15% in bank two. I had my injectors rebuilt and flow tested less than 4k miles ago and replaced the fuel filter at the same time. The car has no codes or lights, not even on inpa (at least relating to the engine). Cant find any evidence of any vacuum leaks too. Very rarely and roandomly my car won’t start on the first crank so I suppose that leaves me with the fuel pump, however the previous owner replaced it less than 50k miles ago and I dont want to replace a $400+ part if i dont have to. Any methods of testing to see if the fuel pump is bad? Thanks!

Read the MAF rate in g/s hot engine idling and post the rpm at idle too. It should be about 4.9 g/s at idle 870rpm. If the MAF reported too low, then the mixture would be too lean and force to high fuel trim.

[OldRanger]

Very rarely and roandomly my car won’t start on the first crank so I suppose that leaves me with the fuel pump, however the previous owner replaced it less than 50k miles ago and I dont want to replace a $400+ part if i dont have to. Any methods of testing to see if the fuel pump is bad? Thanks!

The crank no start symptom was the first symptom of two that preceded a failed fuel pump for me. The second symptom was a fuel pump relay related code (which needed no corrective action). Getting towed was not fun.

Sorry, I don't know of a way to test the fuel pump that is simple. You could set up a test for fuel pressure, but unless that sounds fun to you...the fuel pump might be a time (cost) effective insurance plan against a failed fuel pump. Which, will happen at the least convenient time possible and require a tow as well as loss of use while you wait on parts.

[y2k_o__o]

To OP, I am also in the same boat as you, my LTFT is 20% for both banks and no CEL, my STFT is very normal (well under 4% while driving), this is usually a sign of vacuum which I have been chasing this year !
I replaced these components:
1. injectors
2. all injector / air rail O-rings
3. fuel pump
4. new intake elbow gaskets x2
5. PCV cyclone with new o-rings & gasket
6. valve cover gasket

smoke test shows no leak, so now I suspect all the plastic vacuum hose that connects to the airbox and brake booster.

[tomasidris]

The crank no start symptom was the first symptom of two that preceded a failed fuel pump for me. The second symptom was a fuel pump relay related code (which needed no corrective action). Getting towed was not fun.

Sorry, I don't know of a way to test the fuel pump that is simple. You could set up a test for fuel pressure, but unless that sounds fun to you...the fuel pump might be a time (cost) effective insurance plan against a failed fuel pump. Which, will happen at the least convenient time possible and require a tow as well as loss of use while you wait on parts.

Yeah I think I might just replace it. I was thinking of upgrading to a 255lph fuel pump since I am tuned and have heard of fuel starvation occurring with stock fuel pumps on tuned m3s. Was thinking of going with the dw200 kit.

[tomasidris]

To OP, I am also in the same boat as you, my LTFT is 20% for both banks and no CEL, my STFT is very normal (well under 4% while driving), this is usually a sign of vacuum which I have been chasing this year !
I replaced these components:
1. injectors
2. all injector / air rail O-rings
3. fuel pump
4. new intake elbow gaskets x2
5. PCV cyclone with new o-rings & gasket
6. valve cover gasket

smoke test shows no leak, so now I suspect all the plastic vacuum hose that connects to the airbox and brake booster.

Yikes, that’s no fun. I’ve replaced all of those too except the pcv and fuel pump with no change. Haven’t done a proper smoke test yet but it may be time. Good luck!

[tomasidris]

Read the MAF rate in g/s hot engine idling and post the rpm at idle too. It should be about 4.9 g/s at idle 870rpm. If the MAF reported too low, then the mixture would be too lean and force to high fuel trim.

Yeah maf is reading around 4.3 g/s hot idle. Idle fluctuates from low 870s to high 880s. I cleaned the maf a bit ago and it read high 4s but seems it went down again.

[sapote]

Yeah maf is reading around 4.3 g/s hot idle. Idle fluctuates from low 870s to high 880s. I cleaned the maf a bit ago and it read high 4s but seems it went down again.

With an unstable idle rpm it's hard to verify if MAF is correct or not.

[tomasidris]

With an unstable idle rpm it's hard to verify if MAF is correct or not.

I feel like bouncing idle, occasional crank no start, and high fuel trims tells me I should just replace the fuel pump. Ig ill do that then.

[y2k_o__o]

I feel like bouncing idle, occasional crank no start, and high fuel trims tells me I should just replace the fuel pump. Ig ill do that then.

high fuel trim are most likely:
fuel pump failure
clogged injectors
vacuum leak - I highly suggest you check thoroughly all the flimsy plastic tube / hose that goes into and out from the airbox, particularly :
1. PCV ventilation hose return to airbox
2. 90 deg tube that goes to oil dip stick

These are the common area of failure for vacuum leak

[tomasidris]

high fuel trim are most likely:
fuel pump failure
clogged injectors
vacuum leak - I highly suggest you check thoroughly all the flimsy plastic tube / hose that goes into and out from the airbox, particularly :
1. PCV ventilation hose return to airbox
2. 90 deg tube that goes to oil dip stick

These are the common area of failure for vacuum leak

Had injectors serviced recently and have had the airbox out when doing it and inspected everything under there which is why im leaning towards my fuel pump. If it for some reason doesnt solve it ill do a smoke test.