1994 Explorer Transmission shifting issues

[Flavoade]

Hello guys.

I am posting this for a friend who owns a 1994 Explorer Eddie Bauer 4.0 Auto 2WD.

He received this truck as a "gift" but it has been troublesome for him. He received it with a blown head-gasket and other issues. He had the HG replaced and then the radiator exploded and took out the engine. He had the engine replaced and since then has continued to have problems. As of late he is on his 5th breakdown in 2 months.

He had loose battery terminal issues, a failed starter, and recently blown EEC fuses. We replaced the the EEC fuse the first time and he was good for a week, until the fuse blew again. We replaced the fuse but it kept blowing when he would crank. Last night I found the wires leading to the transmission on the driver wheel well melted to the exhaust manifold. I believe this is the short.

His transmission shifts like crap. From a stop it will hold first gear close to red-line, and at random moments will force itself into 2nd gear and beyond. He drove it like this for months, and I thought it was just a failing transmission. He recently revealed to me that before the motor was replaced he had no issues with the tranny shifting, and said it worked smoothly. He took it back to the mechanic who installed the motor and he said it was working fine.

I checked the fluid and it was full and still red. I added some TransX and it changed nothing. I noticed his Electric Shift fuse was missing so we replaced it but no change. After reading the forums I saw threads of others having similar issues with the EEC fuse blowing and transmissions shifting bad caused by wiring shorts.

From this information, can you guys tell me anything that would be disconnected that would cause the transmission to not shift correctly?

I will repair the wiring going to the transmission that was damaged. I noticed that he has two wires, a red and black, with rings terminals that come through the firewall and are long enough to reach the transmission. Anyone have an idea of what these may be and where they go?

Thanks guys!

 

[natenkiki2004]

Woah boy, that's a heap. Anything could have happened when the engine came out. Did the shop drop the transmission too or did they just pull the engine out and leave everything else?

Usually holding 1st gear too long is the governor sticking but that wouldn't suddenly happen, it would develop over time, getting worse & worse. I fixed mine with a transmission filter (see my signature). I'm heavily leaning on a wiring issue. From what I understand, the wires going to the transmission are on the driver's side fender, leading down to the framerail.

Only other thing I could relate to shifting would be the vacuum lines not being hooked up right, specifically the vacuum modulator. Mixing the lines up is fine (it's all vacuum) but maybe this line was lost or left off or just became disconnected at the modulator itself?

On a side note, I'd be willing to be that the "Electronic Shift" fuse is for the 4x4, specifically the transfer case.

 

[arco777]

Vacuum modulator gets my vote.

 

[Flavoade]

Woah boy, that's a heap. Anything could have happened when the engine came out. Did the shop drop the transmission too or did they just pull the engine out and leave everything else?

I do not know for sure, but the hood shows signs of being removed.

Usually holding 1st gear too long is the governor sticking but that wouldn't suddenly happen, it would develop over time, getting worse & worse. I fixed mine with a transmission filter (see my signature). I'm heavily leaning on a wiring issue. From what I understand, the wires going to the transmission are on the driver's side fender, leading down to the framerail.

After we pulled the wires off of the exhaust manifold, wrapped them with tape, and inserted fuse it is now running, but it still shifts the same.

On a side note, I'd be willing to be that the "Electronic Shift" fuse is for the 4x4, specifically the transfer case.

It is interesting because his RWD. Is there some function that the electricshift performs on a RWD Auto? There are pins in the fuse receptacle so it has wires going to it.

Only other thing I could relate to shifting would be the vacuum lines not being hooked up right, specifically the vacuum modulator. Mixing the lines up is fine (it's all vacuum) but maybe this line was lost or left off or just became disconnected at the modulator itself?

Vacuum modulator gets my vote.

I think you guys hit it hard. Not sure if I mentioned; he has vacuum caps blocking off a few ports on the back of the intake. He said there was one hose specifically that would always blow off. It is a mess under the hood so we didn't know what was what. Do you guys have a link to a diagram or pictures of where the modulator is and how it connects to the transmission through vacuum?

Thanks guys for the all the help.

 

[Flavoade]

I used the the search lol!

I found this thread: http://www.explorerforum.com/forums/showthread.php?t=359540&highlight=vacuum+modulator

From other threads I digested it looks like his modulator is bad and sucked fluid into the hose and caused the blow-off problems, and made the hose break down.

We heard a vacuum leak. Never would of thought the transmission was sucking a vacuum. I take it this the way transmissions were controlled in the past?

Thanks for helping me guys. Any more advice before we start dealing with this?

 

[natenkiki2004]

The transmission does not create the vacuum, the engine does. When the modulator goes bad, it usually leaks transmission fluid which gets sucked into the engine. In this case, it sounds like the modulator isn't even hooked up.

 

[arco777]

The vacuum modulator (vac mod) is fairly easy to get at with the trans in the vehicle. There is a removable access panel in the floor right above the trans (just pull the carpet back). The vac mod is on the passenger side of the trans and has a short chunk of rubber vac line attached. This connects to a shaped hard line that runs up the trans tunnel/firewall. The line has a bracket that bolts to the intake manifold close to the end. At the end near the manifold, another piece of rubber tubing connects the hard line to the vac tree on the manifold. You should be easily able to see the hard line at the rear of the manifold with the hood up.

On the modulator side, the mod is held into the trans by a small removable bracket. The mod comes right out after the one bolt for the bracket is removed. The mod is available at auto parts stores if it needs replacing. Failure of the internal diaphragm causes the vaccuum to suck fluid through the modulator and into the intake manifold. The modulator can seize as well.

Another possibility. The modulator has a small pin in between it and the trans. This pin can get lost very easily if the mod is removed. An amateur mechanic may not notice it missing. Fortunately a new pin can be made. Missing pin=bad modulator symptoms.

Manifold vacuum is used to actuate the modulator, which is a key part of the 1-2 shift. Without vacuum the trans usually will shift very late, often around 3000rpm.