No Overdrive unless I'm coasting. | Ford Explorer Forums - Serious Explorations

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No Overdrive unless I'm coasting.

Wakeboy1337

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June 17, 2010
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City, State
Fort Pierce, Florida
Year, Model & Trim Level
93 XLT
I'm not sure if I dont have overdrive or if I don't have TC lockup. Here is whats happening. I'll be traveling about 55 mph and the engine is doing about 2800 rpm. I'm asking myself WTH so let off the gas and then it seems to go into overdrive, I put my foot back on it to maintain speed and it shifts down again, making the rpm rise back up. I think its overdrive malfunctioning because if I'm coasting and I shift the shifter from OD to D I'll get the same rpm change. Also I've tried driving up to 55 in D then shifting to OD and the rpm doesn't change whatsoever.
 



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That does sound like it is not shifting into 4th gear. Since 3-4 shift is electronically controlled on your A4LD, the first thing I'd probably do would be to pull codes from the computer (even if the CEL isn't on) to see if the computer has any faults to report.

After that, the 3-4 shift solenoid circuit is a pretty basic DC circuit. It isn't very difficult to inspect the circuit with a wiring diagram and a voltmeter.
 






Where is the Vacuum modulator on the trans.? I saw what looked like a hose nipple on top of the trans. but no hose on it and no signs of a hose down there. I don't see any harnesses around this tranny either :-/

I dis-like having to learn new vehicles.


Btw KOEO I got 566. 3/4 Shift solenoid failure

KOER i got 111
 






Vacuum modulator is on the passenger side of the transmission, up alongside the exhaust. The nipple on top might be for a breather hose.

My experience with KOEO codes for these circuits is that it takes either a full open in the circuit or a short to ground to trigger the code. A KOEO 566 should be fairly straightforward to track down with a wiring diagram and a voltmeter.
 






Going to look under the truck tomorrow. Since it will go into 4th when I let off the gas, could it just be the downshift cable being out of wack? Also I did KOEO again today and no 566 this time :/
 






I wouldn't expect it to be the downshift cable. I could be wrong, but the downshift cable forces the downshift to 2/1. I don't think it does much to the 3-4 shift. The KOEO 566 going away suggests to me the possibility of an intermittent circuit fault.

If it were me, I'd still familiarize myself with the circuit, and maybe even put a voltmeter across the solenoid so I could monitor what the circuit is doing while I'm driving.
 






Hitting the books tonight. Starting inspection tomorrow. I'll keep you posted.


How often do these things fail?
 






Replaced both solenoids today. I have tc lockup now :) Still no overdrive. Still code 566.

I put new gasket and filter in, new solenoids, new vacuum modulator. Only goes to overdrive when coasting, with the circuit fault code still active. What is the best way to test the circuit? I checked the connector on top of the trans. and it does get 12 to both sides when I'm in KOEO test mode.
 






3-4 shift and TCC lockup share a common power supply. Where one works without the other, and you have the KOEO 566 which indicates an electrical fault, the fault would most likely be between the "split" to the two solenoids and the PCM.
I checked the connector on top of the trans. and it does get 12 to both sides when I'm in KOEO test mode.
If I assume both were referenced to ground, that suggests that the fault is not inside the trans. Next step would be to continue down the circuit (seems like the next connector is on the driver's wheel well under the hood) and see if you can still see +12 V there. Then check the appropriate pin at the PCM. As I noted before, a KOEO 566 is likely either a full open or a short to ground. If the circuit is intact from the EEC relay to the PCM, then I would start a series of tests to determine if the circuit has failed inside the PCM.
 






Alright Mr. Shorty. Here's what I've been up to all day, I checked the circuit at every, connector, relay, all the way up to the PCM connector. Then I checked the continuity on pins 52 and 57 (I think it was, I dont have a chart in front of me). Everything checks out.

I even did this.
DSCF5189.jpg


DSCF5191.jpg

That is lamp cord joined into the 3-4 ground wire and then the other side of the lamp cord is attached to the ground of the truck. I had my dad ride along with me and put the wires together at 50 mph and it made no difference. There appears to be no short or gap in the circuit. The red wire has to be good, seeing as I have TC lockup. I'm at a loss here. I'm am going to rip my hair out and roll in the grass crying if my new solenoid is bad.
 






We have two conflicting opinions. You say that the circuit is intact. The computer (via the KOEO 566) says that it is not. Because we are following this over the internet, we can't independently verify what you've done. We also don't believe that computers are infallible. If you did what I think you did with your lamp cord trick, the fact that you couldn't get it to shift into 4th gear manually suggests to me that there is still some fault in the circuit.

If it were me, I'd probably go back to what I suggested in post #6 and see what the computer is doing. Backprobe those same pins you used to check continuity, then enter the output state test (see my notes on pulling EEC-IV codes). You should be able to see the computer switching the solenoid on and off by the changes in the voltage (it should alternate from 0 to 12 V). If it passes the output state test, then you can test drive and see when the computer chooses to command the shift.
 






I'll try output state test at the pins on the computer tomorrow.

I would put a multimeter across he solenoid as I drive but how would I even do that? It's inside the trans.
 






When I've done it, I've simply used pins and backprobed the proper pins at the PCM (52 and 57 sound right). You have to be careful not to damage any connectors.
 






Ok I have some more news. I did what you said, multimeter at the pins and right after TC lockup at around 47 mph, the 3-4 circuit was only putting out .22/.23 volts. If I sped up to 60 it would drop to .18 volts. If I coasted it would get up to .24. I had another computer in the truck, it's the one that came with it. This computer is in failure mode. (It literally has burned up traces on the board) I hooked it up and ran the same test. I got 13.4 volts! but no TC lock or overdrive.(I think TC needs to be engaged first but that pcm is shot so it wont engage.)

Btw, with the good pcm I did output state test in KOEO test mode and when I hit the gas the multimeter showed nothing as I cycled it on and off. This was right at the pins.

I see no burnt traces on this board, no leaky capacitors, no loose solder joints, no missing or broken pins.

It was pin 52 and 37 I tested. I couldn't remember without the chart in front of me. Here it is.

Graphic.gif


My guess is that I'll need to buy yet another computer :/
 






Btw, with the good pcm I did output state test in KOEO test mode and when I hit the gas the multimeter showed nothing as I cycled it on and off. This was right at the pins.
Something isn't right. I'm pretty sure you should see it cycle from 0 to 12 V. What do you get from the output state test if you put positive lead at pin 52 and negative lead to ground (should also cycle from 0 to 12 V)?
 






Something isn't right. I'm pretty sure you should see it cycle from 0 to 12 V. What do you get from the output state test if you put positive lead at pin 52 and negative lead to ground (should also cycle from 0 to 12 V)?


I get 12 volts. Then when I cycle the pedal It drops to 11. :confused:

Edit: Took it for another test drive. This time at 50 mph I put a connector from pin 52 to ground and holy crap, overdrive kicked in! but then not even 5 seconds later, it bounce out of overdrive. Then back in, then out. Then it just stayed out. I disconnected and tried again a few minutes later. Same thing. Then a couple more minutes later it wouldnt do anything at all. When I'm sitting in the driveway with the key on and engine off and I make that connection from 52 to ground I can hear the solenoid click in the transmission. One click when I make the connection. One click when I disconnect.
 






I get 12 volts. Then when I cycle the pedal It drops to 11.
Should drop to near 0 (I believe that Ford's official manual asks if it drops below 10.5 or something). This suggests to me that the fault is either in the PCM or in the grounds to the PCM or maybe the PCM 60 pin connector. I would carefully check the PCM grounds to make sure they are good, check pin 52 in the PCM connector to make sure the pins aren't damaged, then I'd probably be wishing I had a known good PCM to put in and test with.
 






If I was broke and didnt feel like buying another computer seeing as this one is good oterwise, Would it be a bad idea to Make overdrive manually controled by me via a switch on the dash? I'll start checking grounds, I looked at all the pins, the seem to be okay(and clean).
 






From what I remember about the grounding of the OD circuit its not actually a ground. The PCM does an internal grounding type thing. If you outright Ground that pin it would burn something up since it would pull too much power from the ECM.

~Mark
 



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BIG NEWS


Overdrive is engaging fully and staying engaged now.

I adjusted the band on the tranny, and then cliped the tc lockup pin and 3-4 pin together for testing purposes. (Will that burn anything up?) When I hit 50 mph on speedo( 54 on GPS) I was in overdrive. :D My truck will do 55 mphs at 1800rpm. Now I have not decided yet what I'm going to do for a perm. fix. Money is a bit tight and a computer is not an option atm.

Btw I did check all the pcm related grounds. Everything was copacetic.

If you have an idea for a good fix for a switch or a way to wire it to turn on automatically, feel free to chime in. When I'm driving the ground wire is only getting .23 volts.
 






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