Codes 25 and 26 - 91 FJ80 (1 Viewer)

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Jacksonville, NC
New owner of a 91 FJ80 with 203,000 miles on it. I’m a self-taught novice mechanic with most of my experience working on vintage BMWs, so these are new to me. Looking for some help on this one.

My CEL came on the other day. I just checked it tonight. It’s throwing codes 25 (lean mixture) and 26 (rich mixture). Anyone know why it could throw both at the same time?

I’m also throwing a 71 code, which from reading the 3FE manual is related to the EGR. The P.O. “de-smogged” the truck. I say that loosely because I’m still finishing the job.

Thanks in advance!
 
New owner of a 91 FJ80 with 203,000 miles on it. I’m a self-taught novice mechanic with most of my experience working on vintage BMWs, so these are new to me. Looking for some help on this one.

My CEL came on the other day. I just checked it tonight. It’s throwing codes 25 (lean mixture) and 26 (rich mixture). Anyone know why it could throw both at the same time?

I’m also throwing a 71 code, which from reading the 3FE manual is related to the EGR. The P.O. “de-smogged” the truck. I say that loosely because I’m still finishing the job.

Thanks in advance!
I was throwing 25, 26 and 71 as well when I purchased the mine. I had a bad exhaust leak before the O2's. I replaced the exhaust gaskets between the manifold and the down pipes and the 25,26 code never returned. I put a small jumper wire on the EGR plug to cure the 71. Good luck
 
25 and 26 are O2 sensor related. I would start with a physical inspection of the wires/connectors for the O2s. They are low hanging fruit.
Also, pull the 15 amp EFI fuse from the under hood fuse block for about 10 minutes. This will clear any past codes and essentially reboot the ECU.
If all checks well and the codes come back, then replace the 2 O2 sensors.
 
I want to close this one out (hopefully): A couple weeks ago I replaced both O2 sensors with new gaskets.

Yesterday, I replaced the manifold to downpipe gaskets, which were leaking like a sieve. I can't feel an exhaust leak from them anymore.

Reset the ECU, and no codes yet. I'm expecting the 71 code to come back, though.
 

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