Speedo fail/running badly

[Kim]

Sorry if this was already resolved somewhere else, but I have to ask....

Every once in a while when driving the speedo will flutter and drop to zero and the engine bucks and misses when it does that. I'm wondering what/where do I have to look to correct that. I have pulled the main harness plug from the firewall and cleaned it up good and it doesn't happen as often now, but still....every now and then. Other places I should be looking?

Thanks!

 

[RonD]

1998 to 2000 Ranger will get Speed pulse from the VSS(vehicle speed sensor) that is located on the rear axle differential, it is also used for ABS(anti-lock brake system).

If this sensor or connection was the problem then you should also get an ABS light, which you don't mention.
You can still check it but most likely not the problem.

If you don't have 4-wheel ABS then the VSS pulse is split and goes to Rear ABS module and the GEM(generic electronic module).
The GEM is programmed for trucks stock tire size and corrects the speed pulse for that.
It then sends the corrected pulse out to the speedometer and computer.
GEM is located behind the radio in the dash.

Assuming no ABS light(ABS light is working right?), the problem could be in the splice where VSS wire splits for ABS and GEM, or at the GEM itself.

Wire from VSS can either be red/pink stripe or Grey/black stripe(pin 9 on GEM)
Wire to speedo will be Grey/black stripe(pin 1 on GEM)

 

[Kim]

Thank you, RonD!

I will check those out. The ABS light does work, but doesn't come on when this happens, btw.

 

[Kim]

Well, it's been awhile. The problem had been resolved....or so I thought but now it's back with a vengeance.

Here's what I've done so far.

-Pulled PCM plug under hood and cleaned contacts best I could.
-Pulled whatever that other plug is under the hood over on the drivers side and cleaned contacts best I could.
-Cleaned contacts on VSS sensor.
-Replaced VSS sensor.
-Tried to intimidate the truck by cussing it out and threatening to drive it right to the nearest junkyard.

Still no results.
The speedo works only when randomly it seems to want to and won't stay working. Meanwhile while it's being a pricksumbitch, the engine runs bad, bucks, jerks, barely any power, backfires through the exhaust on decel like a popcorn popper... The ABS light does come on fairly quick after driving a short distance.
And the kicker here is that when it DOES work, now it does that screaming idle B.S. until the truck is nearly stopped while coming to a stop. It'll even try to pull through town forcing me to keep braking to try to keep it at the speed limit. It did this before, but seemed to have cleared up for a few months after cleaning the wiring harness plug contacts. So now it just alternates between one problem and the other. I imagine I have to fix the speedo one first to concentrate on the idle one after.

My next plan is to replace the entire wiring from the VSS to wherever it goes and retest. I've been looking around here for similar problems to find definite solutions; I must be missing some, or haven't tried them all yet..