Please help with EGO codes
 

Well, my car is still getting the following codes. These are both KOEO:

41 - EGO sensor signal out of range
(EX. 5.0L SEFI); Fuel pressure
out of range-5.0 SEFI / Always
lean

91 - EGO sensor problem due to fuel
pressure of injectors out of
balance / transaxle fault
(shift solenoid 1)


Now these codes bring up a few questions.

1) What is a transaxle fault?
2) What is a shift solenoid 1?
3) Does this mean it is an
injector problem or O2 sensor?

I tapped into the EGO wires at the computer and got readings of .3v under partial load and it only went up to .6v @ WOT.

I am installing a Procharger in a few weeks and don't want to run lean under any kind of boost, so I would like to get this resolved before then. Does anyone have any ideas? Should I change O2's again?

Thanks for any help. As always, it is greatly appreciated.

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Let's nail this one point at a time. First, a transaxle is a front wheel drive transmission. Unless you've done some SERIOUS modifications like Tim the Toolman Taylor, you don't have a transaxle OR shift solenoids. Shift solenoids are devices used to shift gears in an electronic automatic transmission. You have an AOD (non-electric) if automatic, and a T-5 if manual. Pull your plugs & inspect them before going any further. Have your fuel pressure checked, too. This'll eliminate a lot of headaches & time wasted.

Okay, on to your codes. 41 means "No HEGO switch detected--always lean (right HEGO)." 91 means "No HEGO switching detected (left HEGO)." Basically your HEGO's (oxygen sensors) are either shot (been replaced in the last 30-40k miles?) or the heater circuits have a problem. My money is on the latter if your HEGO's are relatively new and not cruddy, and that fuel pressure and the plugs both checked out okay. There's a common ground running to both sensors, and if this connection goes bad it can turn codes like this. Reason being the EGO's need to be heated to kick out a signal (does it run like it's lean???). Only other thing I can think of would be them being contaminated. Have you used RTV anywhere on the engine or sprayed anything into the throttle bore? If you need more detailed info, email me.

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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch http://smilecwm.tripod.com/net3/wink2.gif

Capri- Thanks for the reply.

I have changed the O2's. It was probably a couple of months ago. The car does tend to run like it is lean, popping out of the exhaust (not a full out backfire). I pulled the plugs and they all seem to be fine. All are a nice tan color.

As far as RTV, I'm not sure what you are asking there. I have used it on my car several times as I have changed the heads, intake and cam a few times. Also, I haven't sprayed anything in the throttle bore.

Thanks again for the reply Capri. Anyone else with any ideas?

Well, this weekend I changed my O2's, pulled the battery cable to reset the computer, and I am still getting these codes? Does anyone else have any suggestions. Could a bad MAF cause these symptoms? Is there a way to test for a bad MAF before I drop $185.00 at the local Ford dealer for a new one? Thanks again.

93 did you run the test's I gave you? Any luck?

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Why go to the Ford dealer for a MAF? You can get one from a parts store like AutoZone for about $100. A weak MAF could theoretically cause problems if it's leaning out the mix too much, but then again the computer should be able to correct for this. I asked about RTV (aka Permatex, blue goo, silicone of ANY kind) because it contaminates EGOs like nothing else. Sensor safe is shifty advertising if you ask me. They all give off fumes that affect the readings. I'm still banking on low fuel pressure.

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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch

Hey Rick, I haven't had a chance to run those tests yet. I am going to try tomorrow or Wednesday when I get a little more time.

Capri - You mention low fuel pressure. That's a pretty good guess because if I get below 37psi, the car runs real bad, missing/popping/bad idle, etc... I have to keep it at about 39psi (with the line on, about 44psi with the line off) or it gets almost completely undriveable, bucking and missing. I tapped the O2 wires at the computer and got reading of .3v under light and partial load, and only reading barely stoich at WOT. I talked to the C&L guys today and they said it sounds like a vacuum leak. These do sound like vacuum leak symptoms, but would that cause the code faults as indicated above?

Oh, most definitely it would create problems such as these. You'd be getting unmetered air past the MAF sensor, leaning out the mixture. ANY air entering the engine not going through the MAF is considered unmetered. If your fuel pressure regulator isn't hooked to manifold vacuum (in some cases even if it is), then that would further lean it out. Sounds very plausible to me. Hope you find the leak soon. http://www.mustangworks.com/msgboard/smile.gif

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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch