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Re: tachometer is working erratically
Clean throttle body housing the air by pass ports, sound like this is clogged causing engine to surge up and down trying to maintain proper idle. Local should not charge more than one hour labor to address. But very doable for a handy DIYer
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I just solved this problem on my 1997 with 183K miles . First I checked all of the following:1) sensor on distributor; 2) wires from distributor to back of instrument cluster; 3) connections of wires to instrument cluster; 4) 4 screens going through the soft circuit board to tachometer; 5) the SOLUTION- I removed the tachometer from the instrument cluster and looked at the hard circuit board of the tachometer. On one side there is a plastic square housing about 1/4 x 3/8" soldered to the circuit board that has a plastic screw facing out. it was lose, so I tighten it and now my tachometer is OK. A simple test to check for this type of an error is hit your dash when the tachometer is erratic. if you see a fluctuation based on the tap on the dash you either have a lose connection of some type like this one. Fix is easy, once you have the instrument cluster out you only have to remove the four screws on the back of the cluster holding the tachometer in place. Remove the tachometer carefully and tighten the plastic screw being careful not to over tighten.
I really cannot tell you how to do that. You need to follow the instructions that came with the tachometer.
Please note: I would be very cautious about connecting aftermarket equipment into your computer input or output circuits. These things have been known to cause all kinds of drivability problems as well as make it impossible to pass an emissions test (if it is required where you live).
I have personally seen aftermarket add-on equipment cause everything from engine cylinder misfires to transmission shifting problems to engine stalling and no-starts. I do not recommend using any at all. However, there are usually no problems created by "stand alone" accessories that are powered directly from the battery and do not require splicing into any of the computer circuits.
My professional recommendation on this is that if you think you need a tachometer to operate your vehicle, or you just like the looks of a tachometer bouncing up and down, then you would be money and headaches ahead to buy a vehicle that is equipped with a tachometer from the manufacturer - you may be opening a can of worms that you do not want.
This is just my opinion based on 37 years of experience diagnosing and repairing automobiles (and having to clean-up aftermarket add-on messes) - do with it as you wish.
It don't love you any more!
You need to check and see if you're losing spark or fuel when it does not start.
Listen for the pump to buzz for about 2 seconds when you first turn the key on. No buzz could be relay, fuel pump or its circuit.
If it does not buzz, crank the engine for a few more seconds until you see the oil pressure go up. If it still does not have fuel then the pump or its wiriing may be bad.
No spark could be coil or ignition module or the wiring. Check for power to the coil. Auto Zone can test the ignition module for free. The old idea that when a module is bad its done is NOT true. The module can give intermitent problems. A vehicle can run with a bad module. If you have a tachometer and the vehicle runs smooth but the tach is bouncing, the module is bad.
The ignition module also send a signal to the PCM so it knows the vehicle is running and will send a pulse to the injectors.
COULD BE GROUND PROBLEMS OR THE TACH GOING BAD.EVEN THOUGH CAR SEEMS TO BE RUNNING GOOD IDLING GOOD.SOME TIMES A SPARK PLUG MISFIRE.CAUSING A LITTLE ROUGH IDLING CAUSING TACH NEEDLE TO GO CRAZY.I SEEN ALTERNATOR WITH VOLTAGE REGULATOR GOING BAD CAUSE A POWER SURGE CAUSING HEAD LIGHTS TO DIM A LITTLE THEN BRIGHT WHILE ENGINE IDLING.THIS WILL CAUSE TACH METER NEEDLE BOUNCE AROUND ALSO.