On my 1999 Mazda B2500, 2.5L, the RPM guage sporadically works or mostly doesn't. Is this an easy DIY fix?

THe problem began a number of years ago. First, I noticed the RPM needle would jump from zero to the correct RPM level based on vehicle speed. Sometimes, it would indicate a much lower RPM reading than a higher RPM value based based on my truck's actual vehicle speed would dictate.

Recently, the RPM guage mostly reads zero even at highway speeds.

Any guidance would be much appreciated. I can live with this annoyance but I would like to address this if it is an easy repair or not too expensive.

RPM guage at zero while traveling at 63 mph

 

If engine runs OK then it is most likely a cluster issue, a single wire from computer provides the signal for the tach, could be loose connection
The Tach signal IS the spark timing signal, so if it was erratic engine would also be erratic

Or could be bad tach in the cluster, more likely

1996 thru 2003 Range or /Mazda B-series clusters are interchangeable, plug and play, black or white face
Engine model doesn't matter, nor does manual or automatic(PRND21 plate is removable), clusters were all the same, but clusters did come with or without tachometers

Cluster wiring diagram below
Pin 15 on top connector(C214), is a tan/yellow wire, that's the Tach signal

Swapping just the Tach can be a problem because you have to remove the Needle on the gauge, and there is only one way to get it back on in the correct place, start the engine, and put needle back on so it show correct RPM of engines idle at that time

 

Ron, thanks for replying. Actually, the engine has a slight misfire that I've been dealing with for 5-6 years. I have changed out wires, plugs, coil packs, fuel injectors, O2 sensors upstream and downstream, cleaned out the MAF & IAT sensor, cleaned the throttle body, etc.

My brother suspects the valves need to be replaced or the ECM (computer) needs to be swapped. But, this tough truck keeps on trucking! Odometer reads 445K. She's a keeper but I will continue searching for a good mechanic who can finally solve the engine misfire on my pride and joy.
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When you have a misfire its always best to do compression test first, compression is mechanical so either good or bad no grey area like spark and fuel

But no, that wouldn't effect Tachometer

 

Q. The Ranger & Mazda B series 4 cyl engines have 8 spark plugs - 4 on each side, intake and exhaust. A local mechanic suggested a compression test is next step. He said he would check compression on each cyl both on both sides. I thought just checking compression on exhaust side would be ideal cause it is far easier access but he said he would have to check it on both sides. Does this sound right to you? BTW, he wants to charge $100 to do the test which I find reasonable.

 

No, not right at all

Yes just remove the 4 spark plugs on exhaust side, then test each cylinder and write down results, disconnect 3 wire connector on both coil packs for compression test
Press gas pedal to the floor while cranking engine over, turns off injectors and gives engine max air flow


As for down the road
You can unplug 1 coil pack, the 3 wire connector, and start the engine
The 2.3l/2.5l Lima engines ran fine on 4 spark plugs from 1974 thru 1988, the 2nd spark plug is there to add power, and you can drive it this way as well
If engine is misfiring steadily then 1 of the spark plugs on that side is bad, or its wire
Then reverse it and see if all 4 spark plugs on the other side work

You should do this once a year just to see if a spark plug has failed
On dual spark plug engines it hard to tell if one spark plug fails