I have seen references to splicing a ground to the MLPS ground wire to eliminate shifting problems. Can anyone help me with this? '94, 5.8, E4OD

The transmission shop had it a month, thinking about it. He hoped to find a PCU at a salvage yard to try but never did. He thinks the problem is electrical, not the transmission. I have the ball again and bringing it home.

I have done everything I can think of except this ground and replacing the computer. Am I missing something? Here is the history if you want more info...
https://www.ford-trucks.com/forums/9...lp-please.html

 

What tranny fluid are you using, for requires specific fluid otherwise it wont operate properly? are you sure the filter hasnt dropped which would cause this issue also, i know there is a clip that can be installed easily.

you might go to fsb and look for Paul in the vendor forum, he deals with E4OD's and may be able to get you fixed with an upgraded valvebody?

also the TPS can cause the tranny to not shift properly, even though your not getting any codes for this part you might consider changing it out of its original. Also any thought that your tranny cooler is maybe clogged causing the tranny to overheat

 

Kem, thanks for the thoughts.

Dipstick called for Mercron. I can't find it. Went with Valvoline Maxlife Dexmerc the first time I replaced the solenoid pack. Issues stated out of the blue when Mercron was still in it. Weather was 92 degrees.

Filter had not dropped the first time I replaced the solenoid pack nor the second.

The transmission shop first idea also was the TPS because all the issues are throttle related. I told him I replaced it with Motorcraft about 5K ago. One hole on it is fixed. I adjusted the other to work freely. His next thought was the computer. I mentioned this forum and computers are the last thing thought to fail. He was tring to find a loaner salvage computer to try but never did.

I had never thought of the tranny cooler. It does have the stock towing package extra cooler. The last time I test drove it the weather was 28 degrees and sleeting and I had only driven about 5 miles until the transmission warmed enough to go crazy again.

 

did you adjust the tps after you installed it? have you since back probed it to make sure its operating with in spec's.

I would think any 93-95 bronco 5.8/e4od computer would work as a test. why not swing by some pick N pulls and grab 1.

 

This is my first attemp to fix a transmission so please dont hesitate to comment. Anything is welcome and it may help the brainstorming.

No Kem, since the TPS has one small round hole and is not adjustable on that side I assumed it to be no longer adjustable. The other hole is slotted so I opened and closed the TB until the TPS was not in any bind. Thinking now.......under very heavy throttle it will hold in OD all the way to 75mph. Let off the throttle and it continuously slams very quickly between OD and 3, 3 and OD and the OD button on the stalk has no effect.

No I have not back probed it. I did check the resistance with an analog meter on the old one I replaced trying to fix hesitation. It seemed good. I may still have the old one with about 180K miles on it. Oxygen sensor fixed the hesitation later.

Thinking about it, both the TPS and the MLPS send voltage reading to the computer. Both may be sharing the same ground wire...hmmmmm....I'm going C R A Z Y.

Tentative Plan A. There is a ground to the fender next to where you pull codes. Clean it again. Two by the battery..ditto. Test drive.

Tentative Plan B. Disconnect transmission harness again from the solenoid pack and MLPS to get it out and easy to solder another wire to the MLPS Pin 1 or 4 wire if I can figure out which one is ground and run it to a good ground spot.

Thoughts please?

 

Ok, all of the sensors send some sort of variant of the +5VDC reference voltage (VREF originating at pin 26) with the exception of the O2 sensor BACK to the ECM. The variation is what the ECM is "looking for" from the individual sensors. As for grounding (negative half of the circuit in a vehicle) being an issue, most of the sensors bleed off any excess voltage to negative and send the necessary return to the ECM based on operating/performance conditions. If the TPS is sending "X" voltage back to the ECM via pin 47 then the remaining voltage is sent down the negative. The potential issue is that a weak negative connection (ground) won't let that voltage bleed off and IF the wiring splices into some other sensor's negative (ground) wiring BEFORE hitting a strong grounding location, that voltage will then back-feed into the other sensor/device wreaking havoc on the system by creating erroneous readings at the ECM.

 

Thanks. I read it four times and suspect I MIGHT be on the right path. There does not seem to be a better starting spot than grounds for the moment. Am I correct?

If Plan B is needed I just want to be sure I ground the correct wire an don't fry everything. I plan to drive it home in the daylight Saturday and want to have my game plan ready.

So, do I splice in a ground wire next to the MLPS or next to the other end at the ECM?

 

The MLPS, according to the diagrams and information I have at my disposal, has no negative connection whatsoever. The GREY/RED wire sends the MLPS signal BACK to pin 46 of the PCM. The LT.BLUE/YELLOW wire receives voltage FROM the PCM and alters it depending upon which gear the MLPS is in.

The resistance values between these two wires are as follows.

PARK - 4189 ohms
REVERSE - 1448 ohms
NEUTRAL - 733 ohms
DRIVE - 401 ohms
2ND - 211 ohms
1ST - 85 ohms

I would have posted this long ago if I had realized it was in my arsenal of info.

 

I would also throw your old TPS back on if you have it just for *****s and grins.

 

Great idea Kem. Old TPS goes to plan B now if I can find it. I also located a U Pull It that said they have several Broncos. None of the other local salvage yards have a computer.

GS, here is the article on grounding Shift Pointers 10-98

Note the Gray/Red is labeled ground at the PCM

I also saw a Ford TSB on grounding a F-250 or some diesel somewhere. The above article says this applies to many vehicles.

Thought...here we go again...transmission wiring harness runs from under the master cylinder to the MLPS then to the Solenoid pack on the other side of the transmission. Splicing a ground just before the MLPS might affect both the MLPS and solenoid pack???

Drifting for suggestions...

Remember, this issue is temperature related only after transmission, not engine, warm up THEN throttle position related.

 

If splicing in a supplemental ground is a known remedy, I would say its a classic case of "What's it gonna hurt that isn't already screwy?" I'm wondering now if there isn't some sort of grounding issue that rears its ugly head with age. I mean, if you think about it the transmission is bolted to the engine, true, but the MLPS is plastic and thereby electrically isolated. When dealing in tiny changes in voltage, that small amount of drop over distance through a rather extensive wiring harness could cause problems especially in an older harness with 17 years of exposure to the elements.

Sorry if that made no sense... I'm thinking along the lines of voltage drop and continuity especially in low voltage systems.

 

When I get it home tomorrow... Plan A. There is a ground to the fender next to where you pull codes. Clean it again. Check for a broken splice near it. Two by the battery..ditto. Test drive.

 

Kem, concerning TPS adjustment... "The TPS should not need adjustment, but once the idle screw has been tampered with, the TPS should be adjusted to match." per Ford Fuel Injection » Throttle Position Sensor (TPS) I may have lucked out on my TPS installation not adjusting.

 

when you go by that salvage yard grab a throttlebody from same year if possible and do a complete swap to yours. would be easier then changing the tps all by itself probably.

 

Kem, great idea. When I changed the TPS last year one screw head broke off but the other one came out. Soaking and vice grips got it out finally.