11MPG and Code 41 - FIXED

[whisperer]

My original posts are gone on this problem that told the whole story. Don't know what happened, I'm back to 0 posts, my profile is gone and I seem to be "Reset". Anyway....

I had been having this really crappy running problem where after engine warm up I would lose serious power on the highway. My milage went totally to heck - 11 MPG on a good day. When I bought the truck I was getting about 20 MPG.
The computer kept throwing Code 41 for Oxygen sensor so I replaced that, checked the wiring all the way from the O2 sensor to the Computer and ended up replacing the ECU anyway because I had a known good one. Still throwing code 41. Arggg.
I did all the other normal checks, actually went over everything that I could think could possibly be the problem. Nothing made any difference, Code 41. I did check the fuel PSI during all that and it was good, at least in the shop on my gauge.

OK, the solution. I CHANGED THE FUEL PRESSURE REGULATOR and all the crap went away. I'm posting this in order to try to help somebody else to NOT have to screw around for 2 months trying to find the problem. Note: There was no sign or any indicators pointing to the FPR in this whole scenereo. I guess if I would have hooked up my PSI gauge and clipped it to the windshield and drove until it occured I might have seen something. I should have, I didn't.

Another note: a friend also had the same symptoms on his 4 cyl and I told him to change the FPR and it also fixed his so it's not 2.9 specific.

 

[MAKG]

The FPR problem shows up right away if you measure the fuel pressure leakdown. It doesn't hold pressure and it will drop to nothing very quickly once the engine is turned off.

Another hallmark is liquid fuel in the line. And hard-starting. And carbon fouled spark plugs, especially near the FPR.

Lean codes are caused by just any misfires. HEGO sensors don't know about fuel, just oxygen, and virtually all misfires have both. Including in this case rich misfires.

This is why testing is so important. The entire HEGO feedback system could have been ruled out by a simple voltage probe.

There are at least a dozen potential causes for lean codes. Do not jump to conclusions. At the ABSOLUTE least, a spark plug inspection is called for right away.