96 2.3 electrical issues

[Tlaurin3]

Hello again everyone. Wanted to see if anyone has any insight on some electrical issues in having.

I'm trying to figure out my speedometer issue currently. It works fine when the vehicle has cooled down and stops when warmed. I believe this is the cause. Now I can't figure out if the g.e.m. module or the pcm translates the vss signal for the speedometer. When I hook up my reader to the truck, I always have the vehicle speed. So if the pm translates and sends to the gem, then to the Speedo, it gives me a troubleshooting path.

Thanks guys!

 

[tomw]

I just read about the speedo, GEM and ABS. My ignorance level is high, but I think I got this from the reading. The VSS generates pulses that are too 'fast' for the speedo, but good for the ABS. The VSS signal goes through the GEM where it is dropped back, and then to the speedo. There is a table of numbers/settings to program the indicated mph based on tire size, differential ratio, transmission which somehow get stuffed into the GEM so it 'know' how to treat the VSS buzz it gets. I may be out to lunch, but that's the general idea. You may watch makuloco on youtube to see how he programs a non-zeroed ECM and has to enter that info if you want to see it done. Not real exciting, but he has found a method to reprogram used ECMs from boneyards/etc back to original factory setting.
tom

 

[Still Bill]

Read my recent thread in Electrical section.

My GEM was bad and speedo would stop (with other things) when the GEM got hot. I mean the actual GEM, not the engine temp.

Other things included interior lights, wipers, and auto trans shifting.

 

[RonD]

From 1995 thru 1997 Rangers the VSS is on the old speedometer cable hook up on trans/transfer case, so there is no "correction" needed, it outputs Fords 8,000ppm(pulse per mile) needed for electronic speedometer.
GEM, PCM(computer), and cruise all share this signal.

You can change the speedo gear to correct for rear ratio and tire size, just like when there was a speedometer cable.

My guess is that the problem is the speedo gear or the Worm gear on the drive shaft that drives it.
3rd and 4th picture here: http://www.therangerstation.com/how-to/interior-and-interior-electronics/speedometers-how-they-work/
Shows what you will see on your transmission tail shaft, drivers side, it can be pulled out so you can inspect the gear and usually you can see worm gear condition using flashlight.
Worm gear can be changed by removing tail shaft housing

If both gears look OK, then could be VSS itself, these can be picked up at most wrecking yards pretty cheap, just swap your gear over to the "new" one
If you have an OHM meter this VSS should be 1.4k ohms, approx.

If you have Cruise Control see if it varies speed like speedometer does, if not then VSS/gears are OK, problem is in the speedometer itself or the wire on the back of the instrument cluster

1998 to 2000 did use rear axle ABS speed sensor(VSS) so did need to use GEM or 4-wheel ABS module to correct to 8,000PPM
2001 and up used OSS(output shaft speed) sensor on trans/transfer case which ran to Computer and then it corrected to 8,000PPM and sent that to speedometer

 

[Tlaurin3]

Thanks for all the responses!

So I'm fairly certain that the vss is fine since I can see the vehicle speed display on a code reader as I drive so I can figure that the signal makes it to the ECM. So if it goes from vss, to GEM, to PCM, then I would rule out the GEM right? Or does it split two ways from the GEM? Like it tees of and one goes to the Speedo and one goes to the PCM?

My truck doesn't have ABS. At least I don't think it does. I bought it a while ago but let it sit for like a year and just now got past emissions so I'm learning about everything else.