Hello everyone from a frequent lurker and occasional worker. Let me start by saying that I'm in awe of the wealth of knowledge here on the forum. Whenever I'm thinking of something on my truck I know where to go to find some insight.

Well, I've got a good one. At infrequent times my speedo either: A)bounces all over the place showing maybe 20-30 mph more than I could possibly be going, or B) will not register at all, nor will the odometer, and I don't have O/D.

Now, the common denominator with the bouncy speedo is moisture. Usually happens in warm weather after a rain the night before and has no effect that I can tell on the odometer. When I drive the truck for a few miles it levels out and works right. This is annoying, but livable and infrequent.

The real problem of late has been when I get in the truck after work and it is hot ( I live in Beaufort SC where it tends to get a little steamy -- three days this week over 95 degrees) and the speedo does nothing, the odometer does nothing and I have no O/D. This leaves me redlining the tach and I can't be doing more than 50mph. On most occasions after driving for 5-10 miles the speedo mysteriously just goes back to working and the O/D shifts right in. Yesterday, however I had no luck after stopping and starting numerous times. I get in the truck this morning and all is well

So, after some searching, I decided to look into the TPS. The truck was my dad's before and he has three that were replaced. The local Dodge dealership is quoting me $405 for the TPS. CarQuest quotes $171. So, naturally I decided to try the instructions on the Sticky and go the poto. route.

When I got in the truck this afternoon and the TPS was hooked up everything ran fine, so I figured this is a good time to compare. I assembled the 5k-Ohm Linear-Taper potentiometer per Ouchman and Tuckerdee's instructions and installed the unit in the truck.

With the poto. hooked up the speedo works fine, but no O/D. Tried both ends of the scale to no avail -- just no O/D. I checked and re-checked the wires. Same results. So, just to see what would happen, I disconnected the three prong harness that goes to the TPS, and what do you know -- same results. With the TPS unplugged and no Poto. the speedo and odometer work fine, and no O/D.

So, tell me what could I be missing? The most frustrating thing is that I can never predict for sure when any of these problems will occur. I've wondered if it weren't the temp sensor on the trans, but why no speedometer or odometer?

Any help y'all could lend would be appreciated beyond words.

Thanks,

Tripp

 

I don't know much about the auto's but if I were to guess I'd say PCM or Vehicle Speed Sensor. With the problem being intermitent I'd check and clean all the connections and grounds. FWIW I've always been told to disconnect the battery before pulling the plug on the PMC. Not much help but a place to start.

 

OK, Montana, thanks for the speedy reply but you got me on the PCM. Now what does than mean? It's been a long week and this brain is fried already. The vehicle speed sensor I've thought about also.

In fact, as I sit here pouring over the 1992 Service Manual for D&W 150-350, Ramcharger Rear Wheel Drive Trucks (that's thicker than a NY phone book and guaranteed to stop at least handgun bullets ) it looks like three sensors have a bearing on O/D. I see the TPS, the Engine Speed Sensor, and the Speed Sensor. I could see how the Thermo Sensor on the trans could also have an effect on the situation, especially considering that the problems of late have been during really hot days.

It's just that I can't seem to narrow things down to one or the other, and these sensors are **** expensive!

I'm already planning on going over all the contacts tomorrow anyhow.

Thanks,

Tripp

 

Had this same problem with my truck, it is also a 1992. Checked all the same things you mentioned. I also checked/replaced the sensor on the tranny tailshaft. It was loose. I tightened it up and the tranny worked like a champ............................................. ..............................for a minute. Turns out I needed a rebuild (not saying you do). I was both glad and sad. I was wanting to swap out the big sloppy converter but wasnt wanting to have to do a rebuild. But got a rebuild kit from TCI and a converter from Hughes and havent looked back. I know at least the tranny isnt going to strand me.

Had the same problem with another truck (a 91.5). With this truck I cleaned the TPS and tightened the tailshaft sensor and that was that.

Im sure some of the smarter guys will chime in and be more of a help then I. Good luck with the fix and let us know what you find out.


One more thing to add and you may have already and Im not trying to insult your intelligence. Check the tranny fluid also.

 

PCM= Powertran Control Module or the computer. On my 91.5 it's mounted behind the battery inside the fender I'm guessing thats where it's mounted on your 92. I don't know if the trans temp sensor keeps it out of overdrive if it's too hot or too cold or both but there must be a way to jump it for testing. It seems to me I've read threads on problems like yours you should try to search the forum and you may come up with more ideas. Sorry I'm automatic transmission challenged.............I wonder if there is a government program to help with my disability

 

The TPS has nothing to do with the speedo/odo. You have a problem with the VSS or the signal wires from it.

First make sure it's tight. If it is, take it off and inspect the drive, they often get rounded off and slip. While you're under the truck look over the wires to the VSS and make sure the connector is clean.

 

Thanks so much for the replies Wannadiesel and Montana. I'm going to go over all my contacts today and give them a thorough checking-over.

Any explanation why the Potentiometer rig doesn't work? It seems like a sure thing with everyone else's posts that I've read.

 

Because the PCM needs a vehicle speed reading and it's not getting it. The jumpy/inoperative speedo is the clue here...

Installing the pot fixed a problem you didn't have.

Spend your time UNDER the truck today and you will get better results.

 

So, WD, would I be correct in assuming that at times while the speedo may be getting a signal from the tranny (VSS), the computer may not be. i.e. -- poor connection or ground possibility.

 

From your description of the problem it sounds like the no OD/no speedo problems happen at the same time, correct?

 

WD, that is correct. I lose the speedo, odo. and O/D at the same time for no apparent reason with no predictability. The bouncing speedo happens on entirely different occasions. Unfortunately, have had to work all day and keep my two year old son, so nothing yet to report.

 

My rig does the same thing. It often loses its ability to tell me how fast its going, how far I've gone, and how to get there in 4th gear... Mostly after it sits for a day or two. When this happens, I just get out, crawl under the truck and burn 50% of my body on the asphalt, then wiggle the VSS around. First I turn it back and forth several times, then push it in towards the tranny. 90% of the time this fixes the issue. The reason this happens on my truck (I think) is simply because it's loose. Now this is where I need some advice. Theres a large nut that threads onto the mount for this VSS. Do I just tighten that mother down and it pulls that sensor in, making it tight?

 

Yes, tighten the nut until the VSS is locked down. Don't go nuts on it, it just needs to be tight enough that the VSS can't move.

 

sweet thanks Dave. Now if I can only find a time when the asphalt isn't egg-frying hot so I can get out there and do it!

 

My son is having the exact same problem with his 1992. Keep us posted on your progress.