As strange as it sounds I have searched but maybe I am not searching correctly, and my memory isnt doing me any justice, but my newly acquired 1994 Ranger (4.0, A4OD, 4wd) has an issue with the speedometer. As it climbs, just after 45-55 mph, the needle bounces quite nicely, and continues to get worse the faster I go...

What causes this? Bad connection? Bad sensor? At one time I thought I knew this, but I am drawing a blank.. Ideas? LOL!

 

Rear differential mounted, speed sensor, or it's electrical connectors pins/sockets, or the wiring to it, maybe. The speed sensor is a common problem part suspect, with an acting out speed-o.

The speed sensors output is used by things, like the speed-o, ABS, auto tranny & cruise control, so are any of them also acting out, like tranny shifting, cruise control dropping out, or not wanting to take a set, or the ABS system warning light flashing, or the rear brakes acting out, ect, if so those are indications that the rear ABS speed sensor belongs on your suspect list.

Some thoughts for pondering, let us know what you find.

 

Midwest Dually,

While I cannot confirm that the culprit behind your bouncy speedometer needle is the same as mine, I had the exact same issue in my '94 Ranger and the problem turned out to be a faulty speedo sensor. I replaced it with a $25 OEM replacement sensor from fordpartsgiant.com and I immediately was liberated from having to stare at a jittery speedo needle all day!

I'd definitely look into replacing your speedometer sensor!

 

Based on my experience with my '91, I was going to say it's the speedo cable. But judging from everyone else's response, the '94 doesn't have a cable?

 

Absolutely Amazing! I will be checking into this! Thank you very much!

After posting this, the next day I took the Ranger out for a while. In the midst of my long drive (down dirty county roads) the ABS light came on, and remained on. Then while dodging an elk, I jammed on the brakes. Afterwards, the "Brake" light came on, and stayed on. Once I turned the truck off, and later back on, the "Brake" light went off, but the ABS remained on.

Now, side note... My 95 Explorer is sitting in the shop due to the tranny failing (4r55e) and it being insanely difficult finding another tranny to replace, hence the Ranger being bought. After recently purchasing the Ranger, it came with paperwork showing a new tranny was put in (A4OD), but was not driven at all for the last 6 months. I bought, started driving it, and noticed that it likes to shift around 2500 to 3000 RPMs. I have been butterflying the gas to get it to shift at lower RPMs, as it doesn't set with me well to be shifting that high. It does have a hard shift to it occasionally as well. Having been accustomed to driving diesels, it takes some getting used to this high shifting. Now hearing that the Speedo sensor could be culprit to not only the "speedo" issue, but the ABS and shifting issues.. I am going to look into that!

Thank you!!!!!!

 

We've also had one member report broken wire strands in the ABS sensor wiring harness, where it comes out of the split protective plastic covering, so be sure to check the wiring & insulation & wire strand soundness to the speed sensor electrical connector, as well as it's pins & sockets, for corrosion, bent pins, spread sockets, open circuit wire run, ect, before throwing a part at the problem.

The speed sensor is mounted atop the front center of the rear differential housing. One 10mm bolt & an electrical connector. If you decide to replace the rear ABS speed sensor, lube it's "O" ring before installation & torque the 10mm bolt to 25-29 ft/lbs.

If you have an engine CEL, Cruise Control, Brake, or ABS trouble light/s lit, or flashing, then those systems computers have set trouble codes that can offer up good trouble shooting clues. Most autoparts stores will/can scan the engine computer for trouble codes at no cost, if the CEL is lit. Brake & Tranny shops have special scantools to read their respective systems trouble codes, but they may charge for a scan.
Edit: Check the brake master cylinder fluid level, if the Brake light has been on.

If you replace the speed sensor, first disconnect the battery B- lead, to wipe the computers KAM (& it'll also wipe any trouble codes, so don't do this if you plan to have the vehicle scanned for trouble codes) but doing it after the repair, lets the computer know a repair has been made, so it'll know to begin to relearn some things quicker, using input from the new speed sensor & maybe prevent driveability problems.

Take the time to go through the cold & warm idle relearn routine, by turning off All electrical loads, starting the engine cold & slowly shift into each gear, including reverse, ending in "N" or "P".
Dont touch or turn anything on & after it fully warms up, shift into all gears again & the computer will have relearned it's new cold & warm idle routine. The remainder it needs to learn it can do as you drive in town & on the road, usually without driveability problems.

More thoughts for consideration. Let us know how it goes.

 

PawPaw and BlueOval...

I think you guys are right on the money with this, and have a new sensor coming in this afternoon, so we will all get to find out soon! LOL! As strange as it is, pricing was very cheap for brand new ones with lifetime guarantees. Well under $25, even at Napa!

PawPaw.. Thank you for the code info for clearing the PCM. I will be taking my time and be very methodical at reseting the PCM when the new part is installed! Thank you big time!!