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Speedometer and Oil Pressure Gauge Needle Bounce

I have a Ford Ranger 3.0L 2002 automatic transmission that has 110,000 miles on it. I have a speedometer needle that bounces after warming up for 2-3 minutes and then eventually if it runs long enough the oil gauge will spaz out. I noticed a chirp and replaced the cam synchronizer using similar posts on this forum. The chirp is gone and the old one had play in it showing that it was on its way out. However this did not alleviate the bouncing / flickering needles. It does not seem to show any signs of running poorly like it wants to stall. Thanks for any clues/suggestions.
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I had an 02 3.0 that did the same thing. I never figured it out. I think some people fixed it with a new oil sender.
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Welcome to the forum

I don't think speedo and oil gauge are related, while they do share common wiring in the dash the temp gauge, fuel gauge and voltage gauge also share those wires.

Because it is not expensive I would replace the oil sender/switch on the engine, back by cam synchro you replaced, passenger side top of block
Oil pressure gauge is an on/off gauge same as Oil Light, above 5psi pressure gauge goes up(on), under 5psi is goes down(off), so jumping in this needle could be loose wire or plugged up switch, check connector and remove switch to have a look even if you don't replace it


2002 uses electronic speedometer so needle is driven by a motor in the dash, odometer uses a different motor
Does the odometer seem to "jump around" when speedo does?

If not then signal to dash from computer is not the problem, they share that signal.

Now it could be connector on the back of the dash is loose, but speedo and oil gauge are on different connectors

2002 doesn't use rear axle sensor like 1995 to 2000 did, and that sensor was a common problem, so not your issue
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I just replaced the oil sender on mine for the bounce. After reading many, many threads I wasn't confident it would fix it, but surprisingly it did.

Last edited by 69Stang; 1 Week Ago at 10:47 AM.
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Thanks, BigEdge, Ron, and Stang for the replies.

I ordered the pressure sender switch to replace the original. I will locate the switch and clean up the connector and such.

To answer your question, the odometer does not fluctuate, idle RPM needle is also stable. I am thinking my alternator/voltage regulator might be on its way out. I noticed a significant dimming of lights when I used my power windows. It seems like when I run the A/C or turn the wheel it acts up more (all of these causing changes on the load for the alternator / serpentine belt and such) I have had no engine codes or battery lights, but my cam synchro was definitely going bad and was not tripping any codes. I replaced an idler pulley and the belt about 4 months ago. Does a bad alt/voltage reg seem like it could be a culprit?

Thanks for the replies!
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Yes, alternator most certainly could effect any electrics in the vehicle.

Invest $20 in Volt/Ohm meter, or borrow one

Check battery voltage BEFORE starting engine, this is "at rest" battery voltage
12.3 to 12.8 is expected

12.8 is new battery
12.3 is 5 to 6 year old battery and time to shop for a sale on batteries

12.2 or lower will cause the "click, click , click" no start on the next cold morning

Start engine
Battery voltage should now read 14.5 or higher
It will drop to 13.5 after a few minutes
14.5 is ReCharge Voltage, because battery is drained from starting engine so gets a quick recharge, above 14 volts for more than a few minutes will "cook" the battery and shorten its life

After voltage is down to 13.5 to 13.8, engine idling
Turn on all the lights, leave doors open, set fan to High
Voltage will drop and then come back up to 13.5-13.8, thats the voltage regulator responding to demand for more amps

If voltage stays down close to 13 or under(at idle), then you have a bad Field in the alternator, could be diodes or wiring but it needs to be replaced or rebuilt

No vehicle maker puts in an alternator that can't power ALL the electrics at 650 RPM idle, so dimming head lights is often the first sign that alternator is not producing full power at idle.
And an alternator produces AC Voltage, which the diodes inside change to DC volts, if alternator starts to "leak" AC volts into the electric system then you can get odd results, I mention this because the speedometer uses AC VOLT SIGNAL from the computer

Clean battery terminals, always

Last edited by RonD; 1 Week Ago at 08:52 PM.
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Wait, it's supposed to idle at 650?!
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Quote:
Originally Posted by MaDMaXX View Post
Wait, it's supposed to idle at 650?!
lol, yes, manual trans idle can be as low as 625, like on my 1994 4.0l, so thats the minimum idle/RPM spec for alternator's power output

Automatics use higher idle and later years even higher idle because of emissions requirements
An idling engine is a big polluter

4cyl engines tend to have higher idle to prevent vibration, 180deg firing causes vibrations at lower RPMs
And some "V" engines, like the 3.0l Vulcan don't have enough torque mass to stay running with alt, water pump, PS and AC drag at lower RPMs so are set higher
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Yeah, my 350z idles at 650ish, but interesting you mention the Vulcan, that's mine and yes it is idling higher.
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Ok update. I replaced the oil pressure sender switch. I had the battery/alternator tested and I did what Ron said with my voltmeter and everything lined up exactly where the good side of things is supposed to be. I said screw it and started taking off my grounds and cleaning them up, as I took off the negative cable to the battery I found a piece of buildup on the bottom side that I could not see, despite having the felt washers and some corrosion inhibitors on the cable/post. Cleaned that build up and voila, no more bouncing speedo.

Long story short: Check/clean your battery cables/posts.

Next question: How do I get a stuck oil pressure needle to go back to the other side of the stopper/rest?
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Good find, and yeah, battery posts are a pain for corrosion - i saw recently what corrosion on each terminal meant, can't remember it though :(
I do find FluidFilm is great on posts though.
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