Questions about codes and lack of codes

[matthew]

I finally got sick of chasing ghosts and bought a code scanner so I could quit the guess and replace sensor chase. I ran my 91 Colony Park wagon and got these codes:

11 all clear KOEO (engine off codes)
18,91,41,53,31 continuous memory
and 12,23,41,91,13,74 KOER (engine running codes)

question on the above KOER codes:

41,91 list as HEGO (HO2S) sensor voltage low, system lean
Is HEGO the O2 sensors?

Questions on memory codes:

31 is EVP or PFE circuit below minimum voltage
What is EVP or PFE Circuit?

18 Loss of tachometer input/ IDM circuit failure/ Spout circuit grounded
What do I do for this one, I don't have a clue?

Now for the more compelling mystery. Plugged in the Loveboat (1991 sedan) and got nothing and the scanner shows it is not linking with the computer. I checked the ground plug and had good continuity from the plug itself to the block and hence the ground terminal and from the wire leading to the harness to the frame and block and body. All showed good continuity = no doubt that there is a good ground.

So, what does that mean? is my ECM toast and running on fail mode or something. The car actually run really well except for a high load/ low rpm stumble that is barely noticeable by me and undetectable to most others. However the MPG did go to shit a while back.

Any assistance would be greatly appreciated, glad to see there are so many new members coming here, it is a good place.

Thanks

[gadget73]

41/91 HEGO is oxygen sensors. Lean on both banks probably means you have a vacuum leak somewhere. Possibly related to

31 EVP low. EVP is part of the EGR circuit. Its actually located, *thinks 1991* I think on the side of the upper intake, it looks like a film canister. There is a filter in there under the lid. Pop that out and clean it. It might also mean a stuck EGR valve. Check with 88grandmarq on that, he's the EFI expert.

18 might mean failing PIP in the distributor or a short in the wiring for the SPOUT connector. I'd check the conditon of those wires, and if you've got a spare distributor swap it in. Memory codes also aren't the most important thing. I'd really clear them out, run the car a while, and re-scan it to see whats going on. It may be a condition that was set a long time ago thats been cured and never cleared from the ECM.

As for the no code condition, check this out: http://fordfuelinjection.com/index.php?p=44

[matthew]

I know what your talking about with the film canister thing, the filter inside was disintegrated so I remove but did not replace. I am going to replace that now as well as the tps with is what the other codes indicate is bad. I remember why 18 would be a memory code now. When I set the timing I was running the car with the spout out (obviously) and as a "memory" code it is still there, so I'm not worried about that anymore.

the wagon has 185,000 miles, should i just replace the O2 sensors?

That link is helpful, man it may be a real bitch to track down the problem on the loveboat.

[mrltd]

The 02's prolly could be replaced at that milage.

[gadget73]

I've heard it said that O2 sensors aren't really accurate beyond about 60k, so at 185k I'm sure they're not so hot anymore. It would still be an excellent idea to make sure you don't have any vacuum leaks first though just to make sure you aren't throwing money at it without fixing the problem. Easy way to verify it, hook a vacuum guage up and start pinching off lines. If you pinch off something and the guage jumps, you have a leak somewhere.