Fuel Trim Issues! 1998 540i

[uberKL]

Hey guys, I’m at a total loss. I’ve done so much work on my 1998 540i and I’m trying to get it ready for emissions but I keep getting error P0170 and P0173 for fuel trim on bank 1 and bank 2.
I’ve replaced the fuel pump, O2 sensors, MAF, intake manifold gaskets, injectors, and more. Any ideas on what might be causing this?

[TheAngryBear]

There are a lot of possibilities and without more data we aren’t going to be much use.
Read through this https://www.meeknet.co.uk/e38/Diagnostics.htm
It will give a guide.
You don’t need inpa, just the data equivalent.
We can then assist in reading it and diagnostics.


2001 750iL DD74441
E65 fan & clutch, E65 headrests, Front First Aid Kit, Ultimate Cup holder

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[mattmar1]

as Tab states, you arent giving us much to work with without any data, just the codes. quit throwing parts at the car, unless you just enjoy spending the money. have you had the codes since you started this round of work or did they come along with any repairs done? quite possibly a vac leak, as it is in both banks. inspect all the air ducts post MAF and the vac lines, or have a smoke test done.

[Iforgetalot]

I’ve had the same issues with my 99 540i. High ltft and no clue about how to fix it. I have read post after post, watched YouTube fuel trim tutorials, talked to local shop guys, thrown parts at it, replaced gaskets, smoke tested it, cursed it, smoke test again, prayed, replaced vacuum hoses, gaskets and now they are even higher, LTFT climbing close to 24%. Still no clue on how to fix it. I am seriously considering taking it to the local reputable Indy and have them give it a go.

I believe for this kind of issue you need to be really good at troubleshooting ghost problems and have a good OBD tool.

If I do find the cause to the high trims I will let you know immediately. Please let us know what you find out.

[1999 540i m]

I would check the fuel pressure

[uberKL]

To clarify, there were a host of issues when I got the car and almost all of those parts were repairs that needed to be done. Only one related to the trim that I wasn’t sure on was the MAF but I figured it should probably be done as well. I’m going in to run a smoke test now. Once/if the pending code goes full, I’ll have more data to share.
Minor notes: car idles right where it should (700 with AC on, about 550 off) no misfires, and doesn’t bog or get sluggish.