What does the ECM need to know to shift?

[1Byounkin]

I have a 1991 explorer A4LD and I'm having trouble not going into OD.
Here is what I know (thanks to Maniak):

The TCC locks up. All shifts work but OD.
Have checked ohms on both TCC and the 3/4 and both read good ohms.
I have connected wires to the RED , orange/yellow drove it to see if 12v are being sent from the ECM. No voltage was sent to the transmission for the OD (3/4).
Checked the coolent temp sensor and reads good.
I pulled codes with the koeo test, a code 22 came up. Which is the MAP/BAP sensor. I've read and heard that only a few had in 1991 had used the MAP/BAP sensor. Note: the MAP sensor and the BAP sensor are the same just the functions are change. The MAP sensor was like the MAF now.
I've checked the TPS and it reads good. I know that the VB is good in the transmission and all the other stuff in the transmission.

What does the ECM need to know to shift into OD?

Is it the BAP/MAP sensor?

Please help me with this.

Thanks

 

[Maniak]

One other piece of info..

During the KOEO test, he does see the voltage/signal being sent from the ECM to the trans, so the ECM Is capable of sending the signal.

~Mark

 

[1Byounkin]

Thanks Maniak I forgot that. Got an MAP/BAP sensor today, haven't been home yet to try it.

Anyone ever seen this before?

 

[1Byounkin]

MAP/BAP sensor made no difference.

What about the VSS? Crusie control works. This is the only sensor I haven't tryied yet.

 

[MrShorty]

The information needed for it to shift into 4th gear is the same information needed to lock up the TCC. A little different algorithm to decide when, but it is basically the same inputs. If the TCC is locking up, I would suspect that all the inputs to the PCM are correct.

I have connected wires to the RED , orange/yellow drove it to see if 12v are being sent from the ECM. No voltage was sent to the transmission for the OD (3/4).

Have you tried the same test on the TCC solenoid? The two solenoids are essentially wired the same. If the TCC is locking up, this will give you a chance to see what it is you are looking for.

Exactly how are you doing this test? The test might be working right, but your description implies a misunderstanding of how these are wired in. The PCM doesn't send a voltage to the solenoids -- the solenoids have a constant +12 V sent to them. The PCM acts as a ground side switch (in similar wording to what you are using, the PCM sends ground to the solenoid). If you wire it in right, you can test it manually like you are doing, but it is unclear to me whether you are doing it right.

Normally when I check these circuits, I start by putting a voltmeter across the solenoid (effectively measuring the voltage drop across the solenoid). Then enter the output state test (see my notes on pulling EEC-IV codes in the EEC-IV section) and see if the computer can talk to either solenoid.

 

[1Byounkin]

So what your saying is that they stay hot (12v) all the time? So I should see it go from 12v to 0v?

I checked the wires by tapping into each and put a volt meter on the two wires. As I drove it the OD stayed 0v the whole time driving. TCC locking up fine. The koeo test it had voltage show up between the tcc and the 3/4 (all with the pigtail unplug and the voltmeter into the harness. I checked the ohms on both on the transmission unplug and both read good.
What else can it be?

 

[MrShorty]

I checked the wires by tapping into each and put a volt meter on the two wires.

I apologize as I try to piece together exactly what you are doing.

If I've understood correctly, you tapped into the red wire, put a voltmeter to it (negative probe to ground I assume?) and saw 0 V, is that correct? This red wire is the power wire to both the 3-4 shift solenoid and the TCC lockup solenoid, and it should have +12 V whenever the key is on. Because this powers the TCC lockup solenoid, if this wire didn't have 12 V, the TCC wouldn't lockup.

With the wire tapped into the O/Y wire that goes between the 3-4 shift solenoid and the PCM. Again I assume you have the positive lead tapped into the O/Y wire with the negative probe to ground (effectively you are measuring the voltage drop across the "switch"). Because it is a ground side switch with a constant power supply, you should see +12 V whenever the switch is open (not shifting into 4th gear), and the voltage drop should go to 0V when the PCM closes the switch. Because you are seeing a constant 0V (assuming I have interpreted your test setup correctly), this suggests to me an interruption in the circuit upstream of the test point.

 

[Maniak]

MrShorty,
when I explained to him how to test the circuit I said to check between the red wire and each solenoid wire. IIRC, it will read 0v until the ecm sends the signal to the solenoids and which point it would read 12v.

That is how I "think" I remember it.. Its been a long time.. I could have sworn it would read 0v since the signal wire for the solenoid would not be grounded yet, it would be floating at that point.

did I remember incorrectly and tell him the wrong way to test it? I "thought" he got it right since during the KOEO he saw 12v during the test but nothing when driving(at least thats how I understood his test results).. .

~Mark

 

[1Byounkin]

I did check between the RED and the O/Y and the RED and TCC wires on the koeo test and got 12v on both. But when driving, with the wires tap with a voltmeter on them, the voltage on the 3/4 solenoid stayed 0v. The TCC locks up all other gears work. Maybe I'm doing something wrong.
Sorry to confuse anybody, just never done this before.

What is the right way to check the current? You see what I did.

 

[MrShorty]

MrShorty,
when I explained to him how to test the circuit I said to check between the red wire and each solenoid wire. IIRC, it will read 0v until the ecm sends the signal to the solenoids and which point it would read 12v.[/quot] Sorry I'm slow on this. So we have meter + attached to the red wire and meter - attached to the O/Y wire, correct -- measuring the voltage drop across the solenoid, correct? In that configuration, you are correct, you should see 0V drop while the switch is open, then, as soon as the switch closes, it should show 12V.

Have you run the output state test with the meter wired in like this? If you don't see the PCM switching during the output state test, that begins to suggest that the PCM "can't" command the shift into 4th gear. if necessary, you would need to adjust the position of your test leads until you are just looking at the PCM and verify that the PCM isn't closing the switch. If you see during the output state test that it can command the shift, then you'd need to look further into why the PCM is not choosing to command the shift.

Are we all on the same page now? Again I apologize for coming on line so slow.