E4od not shifting and no tachometer... not sure what to try next

jonleroy2506

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Hey all,

I am new to this forum, I have read a lot of posts but this is my first. I know that there are a lot of posts related to this issue, but I have read over a lot of them and I can't seem top find any that adress quite the same issue as I am having. I have been digging for several weeks now and still am not sure what to do about my e4od transmission not shifting well. I think it is in limp mode but the overdrive light isn't flashing like many other people mentioned. I have not replaced anything yet because I don't want to throw money at parts and still get nowhere. There is one symptom my truck is having that I have not read about in any other threads that I hope may be an indicator to the issue

The first thing I did was check fuses and lo and behold the fuse for the tachometer was blown. I had read that a failed tach or one that isn't sending a signal can cause limp mode in the e4od so I switched the fuse and it blew again, several times. Is this a short circuit somewhere? Is it one of the two relays near the drivers side firewall? I tried tracing wires from the cluster back through the firewall to the relays but I really am not sure which wires I should be looking for specifically. At this point my next best guess is going to be to replace the brown relay on the drivers side near the firewall in hopes that that will fix the problem. Any suggestions would be appreciated.

Also one last thing, I read in a couple of posts related to this issue something about a fuse in the engine compartment, but I don't have a fusebox under the hood and dont know where to start looking for this fuse I read about. Is that only on later models (I have a 1991 7.3 idi ats turbo)
 

79jasper

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When it is dark, see if the O/D light is dimly lit.
Another thing to check is the plug going into the transmission. See if it's full of oil.

Sent from my SM-N960U using Tapatalk
 

jonleroy2506

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Thank you for the quick reply.

I just got down under the truck and in the brief time I was down there (there is a lot of snow on the ground here so i tried to stay out of it as much as possible) I found two connections to the transmission. One was just above where the shifting linkage attaches to the transmission, and that connection seemed very clean from what I could tell. That was on the drivers side. On ther other side there was another connection that I couldn't reach because of a heat shield protecting it from the exhaust pipe. Is one of these the connections you are talking about? Or is there one I missed?

Also, when it is dark will the od light be dimly lit without a key in the ignition?
 

Selahdoor

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You'll have to have the ignition on to see the light. Possibly have to have it running.

Before crawling in the snow again, go around the the front of the engine. Unplug the tach sensor.

Then see if the fuse blows again.
 

jonleroy2506

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Okay I will have to try that selahdoor. Sadly I can't right now because Im charging the truck, as of a couple days ago it won't hold a charge for whatever reason. If the fuse doesn't blow with the tach sensor unplugged what will that tell me?
 

Selahdoor

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That the sensor has grounded out internally and needs to be replaced.
 

jonleroy2506

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Okay I managed to start the truck and check the fuse, which blew again but that served to remind me that none of my electronic gauges are working right now, which probably makes whether or not the tach sensor works obsolete. Some of the dash lights still work which would lead me to believe that the cluster is getting power, so the cluster must still be good. Does that spell some sort of short curcuit to the gauges or would the whole cluster stop working if there were a short? The back lights for the cluster don't work either. Not sure what to try now other than chasing wires... could it still be a relay of some sort?
 

quickster

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Pull that heat shield when you can and check that plug. It has to be super clean. If you can blow out the plug on the trans it would help.
 

quickster

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If the batteries aren't holding a charge for long, you're bleeding voltage out somewhere.
 

IDIBRONCO

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(there is a lot of snow on the ground here so i tried to stay out of it as much as possible)
Not any help for your tach, but here's a little trick that I've done before. I used a cheap plastic sled to lay on in order to slide underneath my truck in the snow. I even used it to change oil in the winter time (before I had a garage to work in). It sure makes sliding under the truck easier. As a bonus, it makes it WAY easier to drag a deer out when there's snow on the ground.:Thumbs Up
 

jonleroy2506

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I decided to just throw on a pair of coveralls and risk getting a little wet to pull that heat shield and connector and it was definitely a little oily. I cleaned it up as best as I could which truthfully probably wasnt really well but I couldn't get an air hose out to the truck and now ive got a voltage issue to work through. Should I try replpacing the dash cluster? I know that sure isn't a cheap replacement so I'd rather keep digging into a possible short somewhere between the fuse and the dash. At this point I'm running on the assumption that the trans is in limp mode because my tachometer isn't working, which at this point I think is the result of an electrical short curcuit somethere between the fuse and the cluster. Does that sound like an accurate assumption?
 

david85

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This one does kinda ring a bell. I seem to remember the 1988-1991 trucks have the transmission controller mounted behind one of the kick panels. Driver's side, I think. It's possible that water got to it. It has a metal case, so any kind of water over a longer period of time will have some telltale signs of corrosion.

EDIT: After some further searching, I found other information that shows the transmission controller may be in the engine bay, tucked against the driver's side corner of the firewall.

For a plan B:

Check the tachometer sensor at the front of the engine near the oil filler cap. Its a big 1" nut with two wires coming out of it. The wires sometimes fray at the sensor, which can cause a short. Try unplugging the sensor and see if a fresh fuse still pops. Something else to try is to disconnect the transmission connector again and see if it still pops a the same fuse. I'd suggest going down one notch in fuse rating to prevent any further damage to the wiring, if you decide to try the "pop-test".
 
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