CEL off, PCM won't erase codes 93 XLT

[rdodd1024]

I have a 93 Explorer. It shows codes 56, 66, and 29. The MAF and Vehicle Speed Sensor were changed. They were out of range. I tried resetting the PCM, by using the scan tool, doing it manually, and even disconnecting the battery. If you check for codes imediatly afterward, the codes are still there. The check engine light stays off, even after 6-10 miles at 45 MPH. If you try reading the codes manually using the CEL, you will get the codes, but under normal driving conditions, the light stays off. It also will not shift into OD or lock the torque converter - the transmission is freshly rebuilt, new converter, and everything seems to check out. I am kind of at a loss - especially since one code means voltage reading is low, another voltage reading is high - it sounds like the PCM has gone to Bermuda for the winter. Ideas?

 

[MrShorty]

1st thought: Are those KOEO (before separator pulse) or memory (CM, after separator pulse) codes? KOEO codes, because they are set during the KOEO test, represent hard faults and cannot be cleared by simply unplugging the computer. These have to be cleared by fixing the cause of the fault. Though you've replaced the VSS and tghe MAF, remember that codes don't point to sensors, they point to circuits. You may have faulty wiring or something isn't plugged in. Only blame the PCM after you've eliminated all other possible causes.

 

[rdodd1024]

Those are from a Key On Engine Off test. I tested the MAF and VSS by the book, and they were both out of range. The MAF had an open circuit. The VSS had low output. The new ones were in the range specified by the book. I have reset the codes on another vehicle with simular problems (92) and it cleared them until the engine was run again. Mine will not clear at all. I suspect the PCM because I had some "help" at one time, when I just finished up heart surgery, and he was quite the idiot. Quite good at shorting things out, not tightening bolts enough, etc. I have tested the wiring harness as much as I can without a breakout box, and everything appears ok. I have one more thing to do monday before I decide what is going on. I know the engine running "hard codes" will not reset until repair, but these should reset with battery disconnect. I also do not understand why I would get a code for too high a signal (MAF) and too low a signal at the same time. That makes no sense. Taking a reading on the MAF connector while running shows normal voltage readings. It is neither high nor low. The vehicle is in good shape and has not exibited any electrical problems at all. I am not going to jump on the PCM as the cause until I have good evidence, as it is about $170.00 exchange for this one - I hate throwing money at things like this, hence my post.

 

[MrShorty]

After clearing the codes are you getting 11 for the memory codes? There are two types of codes output during the KOEO test. KOEO "hard fault" codes which are hard faults just like KOER codes and can't be cleared by simply disconnecting the battery. KOEO codes are output first, before the separator pulse. The second set, after the separtor pulse, are the memory codes. These are the codes that can be cleared. Hence, the question, is it clearing the memory codes?

 

[rdodd1024]

No, and the CEL stays off after startup.

 

[410Fortune]

well I have seen PCM's go south and do strange things. Do you have a buddy with a similar truck to yours? (same year, same trans) you can swap computers with real quick?

I would not be too worried about codes in memory if the CEL is not on and its running fine, likely they will go away. However when did it start not shifting into OD and the lock up no working? those two functions are controlled by the PCM, but if it started after te trans rebuild then it could be many things.

 

[rdodd1024]

It did that before the trans rebuild, and it ran pretty funny for awhile, really rich, stutter sometimes like way overly rich then clear out.

 

[410Fortune]

was the CEL on when it acted funny? Has that problem gone away?

 

[Glacier991]

and if you want to borrow my breakout box you can. The lack of OD and no 3-4 shift strongly suggest a speed sensor input issue.

 

[rdodd1024]

A4ld

Yes, the CEL was on when it ran funny. That has cleared up, it runs fine, and the CEL Stays off. It did have code 29, which is VSS, and I replaced that, because it did not give much signal when spun. The new one (a real ford one) has much stronger signal. I checked the cable as far as I could, I could see no damage to it. I may have to use a breakout box - I am considering it. I am trying to get the rest of this vehicle right.

 

[rdodd1024]

A4ld

Ok, so I checked it out some more. It actually IS shifting into 3rd. I don't believe it is making 4th, but may. I have a new VB to replace the one in it, and it is in massively better condition than the original. The spools all work real nice. Very smooth. I could not get VB gaskets till tomorrow morning, because of my work, otherwise I would have put it in tonight. It shifts very easily when you let off the throttle. It has a new modulator, standard type, hoses are good, and there is good vacuum. Could the modulator be flaky? I think we will have time to do line pressure tests tomorrow night.

 

[410Fortune]

Your posts are confusing.
Do you still have the code 29? (VSS)
This would explain lack of OD shifting, the PCM wont shift the trans without a signal from the VSS, truck wont do OD until over 45 mph.

 

[rdodd1024]

A4ld

I do not understand why they would be confusing. I have tried to make it clear.

1. I got a code 29 when I pulled codes.
2. I checked the wiring to the VSS, checked for signal on it by spinning it
like the manual says, and it appeared low
3. I ordered a new VSS from a Ford Supply house.
4. Testing the new one the same way, output was over twice as much.
5. Installed VSS, CEL is now off when running, it was intermittently on
Before.
6. Pulled codes, 29 is still there.
7. Decided will probably have to check it with a breakout box, to determine
whether it is in the wiring or PCM.
8. I am going to change the VB tonight, for other reasons, and it MAY clear it
up, though I don't 100% expect it.
9. I have made arraingments to use a breakout box and trans tester. I WILL
locate the source of this problem.
10. Thank you for your responses. I appreciate any help and thoughts you
guys have on this stuff. 2000 heads are better than 1.

 

[410Fortune]

CEL is now off when running

K just because you said you had a code 29, then installed new VSS and checked the wiring, never said the new VSS fixed the code.

We are not worried about codes that you used to have and have now been cleared, you fixed them. This is also an indication that the PCM is working.

break out boxes are cool, Ford charges a TON to hook them up and diagnose. I had a 93 PCM go south and after two weeks of trouble shooting I bit the bullet. 1 hour and $350 later ford determined it was my PCM, not wiring.

 

[rdodd1024]

Ford CD Manual

Ok, so I got ahold of the Ford Manual with the EVTM, etc. It is damn good, and shows the codes to mean something else than Haynes, or the code readers manual. It now makes sense, and I will be doing diagnostics most of tomorrow morning. I plan on finishing this thing TOMORROW.

 

[rdodd1024]

cel

The tests show th PCM bad, and I am getting a new one this week - have it ordered. I am still suspecting the connector on the trans for Torque converter lockout, but the codes have to be cleared first, and the way it was acting, the pcm is bad.

 

[Glacier991]

When you get time please post a little about the tests you ran etc ? Might be instructive .....the methodology, etc. If not just showing the value of a breakout box.

 

[410Fortune]

How do you know the PCM is bad? I mean I am not questioning you just wondering what determined this.
this would be number 6 that I know of, 4 of them have been 93 model year Explorer PCM's.