Decided to start a new thread since i let the old one die out. I’m genuinely at a wits end with this thing and i’ve scourged just about every thread on this website and have found nothing that matches my issue.

a month or so ago i started running into an intermittent limp mode with my ‘94 Lightning. no pattern at all, it would do it both hot and cold. Some days it would go ahead and shift just fine, sometimes it would go into limp mode again. it hangs 1st until about 3k RPM then slams into second. i’ve worked around this by manually shifting 1-2 then letting of the gas in drive and letting it find 2nd. sometimes a cycle of the key fixes it, sometimes not.
I made sure to install a temp gauge to monitor the issue and see if the issue was temperature dependent.

I started off with the solenoid pack since the old one had ATF intrusion in the connector. I replaced with a reman unit from cobra transmission that i made sure to test and it ohmed out fine. It shifted fine afterwards.. Until it didn’t.

I then went ahead and dropped the pan again and replaced the fluid and filter with motor craft stuff. Topped off and at the moment the fluid level is where it should be.Truck shifted good. until it didn’t again.

MLPS is indexed properly. the alignment marks on the sensor are aligned properly as well. the sensor is the updated version and was replaced a couple of months back.

I then went and replaced the pigtails to the solenoid pack connector and to the MLPS since the one to the solenoid pack was burned up and the one to the MLPS had some corrosion on the pins. This fixed the issue for about 2 drives, until it started doing it again.

I made sure to match up every wire one by one and on the initial drive it DID work. it shifted beautifully until randomly didn’t anymore.

I’ve finally pulled codes and i come back with this:
654/634- MLPS signal fault
452- VSS signal fault
565- solenoid circuit fault

I go to check resistance at the speed sensor, and i’m getting OL. this means my speed sensor would be the culprit no?

So now my questions are:
-wouldn’t the speed sensor throw an ABS light and kill the speedo?
- i have an LED 3rd brake light unit, but the trans shifted fine with it. would this still be a viable culprit?

- The times where the trans does shift fine would rule out a mechanical issue, correct? since when it does shift it shifts fine.
-can the MLPS cause these INTERMITTENT issues? wouldn’t it fail snd stay that way? as if it shouldn’t fix itself when i reset the battery or cycle the key, or fail randomly.

Any help would be greatly appreciate it and if you can, please drop any helpful knowledge since i know many of you on here are transmission wizards. TIA and hope everyone has a happy 4th.

 

Either of these can cause your problem. You'll need to fix both to get it running right.
That code means Canister Purge 1 solenoid/circuit failure. This is part of the evaporative emissions system, not the transmission. It is not related to your transmission problem.
It means either the sensor or the wiring is bad.
Not always.
No. It can affect the torque converter locking, but not shifting.
Yes, that rules out a mechanical issue.
It indicates that it is more likely to be a problem with the wiring to the sensor than a failed sensor.

 

Thanks for your input Mark. i was praying you’d find this thread sooner or later. i’ll pull the harness tomorrow and ill make sure to report back with any abnormal findings in the harness if any.

 

When my MLPS began to fail, it took several months before the issue really became a worry. I would get the odd little hiccup than would be fine for awhile etc. Eventually , my trans popped into neutral at 60 mph on a busy highway, when I let off the gas pedal, it slammed into gear. I went straight to my local trans shop and had them replace the MLPS. It has been fine since.

 

Mark, i’ve pulled the harness and verified for continuity across all pins on the MLPS and Solenoid pack to the pcm connector (one big round one and one small square one) i have verified continuity and less than 0.5 ohm in every pin, measuring from MLPS/ Solenoid to PCM. i made sure to wiggle the harness and i did not lose continuity in any pin. there seem to be no corrosion or chafed wires in the harness. i made sure to wrap up the harness good with some plastic tubing and felt tape. I also measured resistance in every gear at the MLPS. the resistance values are all in specification.
This time I pulled out the VSS. cleaned it off and checked for resistance. around 1900 ohms or so. guess I didn't have a proper connection last time I checked. Now what? I've tested and tried just about everything I can.

 

If the harness is good and doesn't have any shorts to ground or power, then the MLPS is bad. There is a failure mode where it reads fine sitting still, but going down the road vibration causes intermittent open circuits.

 

im more than sure this is going to be it. I also noticed I have no reverse lights either so im more than sure it's going to be the MLPS. its the only thing I could think of that will kill the reverse lights and throw the trans into limp mode. now for the other question: the OE part is obsolete, so what would be a good quality replacement? my two top picks are either from Rostra or Standard motor products.

 

Mark, i’ve replaced and re-indexed the MLPS. still no reverse lights. as of now it hasn’t fallen back into limp mode again which is good, but i fear that driving it like that for so long might have damaged something. i now have a rough 1-2 shift, almost as if it had a shift kit or if the 1-2 accumulator spring was messed around with.

 

That is possible.

 

Hey Mark I got basically identical issues as the original post but no codes, PSOM was serviced 6 months ago, VSS sensor was changed with standard but original sensor was put back since it didn’t improve. Pigtail to VSS was changed and drove fine for one drive cycle, I scanned for codes again and nothing had came up. 96’ 460. Truck sat for most of its life so there isn’t corrosions in the connectors that I checked. Any tip or direction to look at next would be appreciated. Thanks in advance

 

Did you get a pass code, or no codes at all?

 

Thanks for getting back to me, no codes. My mechanic scanned it with a FORD OBD1 reader and with a snap on and nothing came up then 1 month later when it did it again I immediately bought a scan tool and nothing came up with both OFF/ON test

 

Then chance are the PCM is bad. If nothing is wrong there should be a code 11, which is the system pass code.

 

Perfect thank you Mark, I'll take a look into it

 

Hey Mark, pulled the PCM and inspected for any leaking capacitors and didn't really see any at least to me. Judging by this photo is it possible for you think I can rule this out or should I still send it off for testing? Thanks in advance