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-   -   P0171 P0174 Check Engine Light CEL (https://xoutpost.com/bmw-sav-forums/x5-e53-forum/115443-p0171-p0174-check-engine-light-cel.html)

JPuma 10-27-2023 12:57 AM
Quote:
Originally Posted by workingonit (Post 1234224)
I have a comparison from the day I switched from my stock Siemens MAF, to using the $20 ($23 then) Amazon MAF. First is the Siemens' reading, then the initial reading of the cheap MAF, and a third reading a little later on that day. I didn't zero-out my fuel trims, as I was primarily interested in the MAF readings.
Attachment 83641

Per JPuma and andrewwynn, the Siemens reading was already pretty good, but the cheap MAF readings were actually a bit high (but that kept the fuel trims from setting lean codes). Since that day, the lowest idle MAF reading I've seen was 4.1 g/s, and the highest was 6.1 g/s. I'm still hunting for a vacuum leak.
The OE is really the best bet, but I do think there is something else going on why your fuel trims are so high.

andrewwynn 10-27-2023 08:01 AM
Logicality just the MAF. The reading reported is almost exactly as low as expected by the % fuel trim error.

racebmwm3 10-27-2023 10:36 AM
Quote:
Originally Posted by andrewwynn (Post 1234218)
JPuma did the measurement and yep.

4.35 is the center of the range.
Ok I have a cheap Amazon MAF on the way. Should be here tomorrow.

I’m going to check that MAF wire.

Whatever is going on, CEL is definitely dependent on the car being warmed up as it triggers after driving.

racebmwm3 10-27-2023 10:41 AM
Quote:
Originally Posted by JPuma (Post 1234222)
This was a recent discovery for me. I had a bad maf wire for a long while. tried two MAF's to no avail. my problem was intermittent but didn't notice until I started monitoring airflow. Finally replaced the wire and its been stable since. I may have killed my Cat's because of this.
You have the part number for the MAF wire?

JPuma 10-27-2023 10:57 AM
Quote:
Originally Posted by racebmwm3 (Post 1234238)
You have the part number for the MAF wire?
I actually just purchased a wire from Autozone.

Duralast / Turn Signal Light Connector (no idea why it's listed as this lol)
Part Number:
789
https://www.autozone.com/electrical-...789/884233_0_0


I was going to buy parts from the FCP Euro, but I didn't want to wait. plus you have to crimp pins on the wire.

https://www.fcpeuro.com/products/bmw...or-12521427222

https://www.fcpeuro.com/products/bmw...lk-12521427612

JPuma 10-27-2023 11:08 AM
Quote:
Originally Posted by andrewwynn (Post 1234233)
Logicality just the MAF. The reading reported is almost exactly as low as expected by the % fuel trim error.
Can a MAF give a good reading at idle but then not really respond well as more air is introduced, showing less air that is coming in?

Took my car for a ride last night after having my fuel filter/pressure regulator replaced.

What I have been seeing after the wire repair is barely any adjustments in LTFT when I am mostly idle or doing local driving.

When on highway, steady driving. LTFT goes to 2.13-3.19 ish. Bank 1 is lower than bank two. But after the fuel filter replacement, the LTFT has been even in both banks. but still around 2.13-3.0. when i get off highway, the LTFT starts to drop.

This could be normal but I am not sure. I'm also planning on either replacing my fuel injectors or cleaning. I may just replace as they are original from 2001 and I am trying to overhaul as much as I can.

racebmwm3 10-27-2023 11:14 AM
Quote:
Originally Posted by JPuma (Post 1234240)
Can a MAF give a good reading at idle but then not really respond well as more air is introduced, showing less air that is coming in?

Took my car for a ride last night after having my fuel filter/pressure regulator replaced.

What I have been seeing after the wire repair is barely any adjustments in LTFT when I am mostly idle or doing local driving.

When on highway, steady driving. LTFT goes to 2.13-3.19 ish. Bank 1 is lower than bank two. But after the fuel filter replacement, the LTFT has been even in both banks. but still around 2.13-3.0. when i get off highway, the LTFT starts to drop.

This could be normal but I am not sure. I'm also planning on either replacing my fuel injectors or cleaning. I may just replace as they are original from 2001 and I am trying to overhaul as much as I can.
Shouldn’t you be monitoring short term fuel trims instead?

JPuma 10-27-2023 11:28 AM
Quote:
Originally Posted by racebmwm3 (Post 1234241)
Shouldn’t you be monitoring short term fuel trims instead?
I do, but values are normal when idle, just bouncing up and down within range. As I understand it, LTFT is the result of where your STFT is averaging out, so LTFT adjusts for that.

racebmwm3 10-27-2023 01:22 PM
Quote:
Originally Posted by JPuma (Post 1234239)
I actually just purchased a wire from Autozone.

Duralast / Turn Signal Light Connector (no idea why it's listed as this lol)
Part Number:
789
https://www.autozone.com/electrical-...789/884233_0_0


I was going to buy parts from the FCP Euro, but I didn't want to wait. plus you have to crimp pins on the wire.

https://www.fcpeuro.com/products/bmw...or-12521427222

https://www.fcpeuro.com/products/bmw...lk-12521427612
Not sure if you’ve measured continuity in these wires but this is what I got:

Wires 1 & 2: 4.669 kOhms
Wires 2 & 3: 10.58 kOhms
Wires 1 & 3: 3.763 kOhms

andrewwynn 10-27-2023 01:24 PM
Is that the measurement off the MAF?


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