Question: Are the codes saying the voltage is high or out of range because it running lean/rich, or is it telling me that there is some other problem in the O2 sensor circuit?

I'm trying to diagnose the dreaded idle surge and running rich at all rpm's on my 93 F-150k 302 4x4. MAP, not MAF.

After CEL comes on it throws a KOEO code 41c "HEGO sensor out of range /always lean". KOER shows a 42R HEGO sensor voltage high/system rich...and believe me, it's RICH!

This before AND after a new O2 sensor, plugs, cap, rotor and IAC check/clean. I know I have other sensors and vac leak and BS to check, but the code baffles me: Is it saying the voltage is high or out of range because it running lean/rich, or is it telling me that there is some other problem in the O2 sensor circuit? I checked the fuse for it, it's ok.

 

The fault codes are the result of the other problems.

Fix the vacuum leak first. It's not a BS problem, it's probably the root of your rich mixture and the surging idle.

With a vacuum leak, the PCM cannot properly balance the mixture which leads to all your symptoms.

Steve

 

Thanks...I wasn't using BS to mean unimportant, more like aaargh I don't have time for this.

I'm gonna throw a coolant temp sensor at it first, then chase vacuum if that doesn't work.

 

Why? There's nothing in your post that indicates there's anything wrong with the ECT.

Fix the vacuum leak first.

 

On the 86-97 Forum (and on the advice of a couple mechanics) The ECT has been implicated as a culprit. IF it's failed, it could be sending the wrong signal and telling the computer that the engine is cold, and needs more fuel. So I'm told. (Note: it didn't help).

That there might be a vacuum leak is also educated guessing at this point. I guess I was unclear in the OP. I'll start testing for vac leaks now that I finally located my vac gauge.

 

Fixed it! It was the fuel pressure regulator, the fuel pressure was up to 80lbs instead of 35, overpowering the injectors.

Of course, after spending $70 at Napa and an hour cussing at it while fiddling, I find out it (the FPR) is a recall item on my truck, and Ford would've done the job for free. BUt at least she's purring again.

 

Glad you got it figured out, sorry about the late notice on the recall.