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Erratic Tach


ricks99
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1997 Pathfinder LE with 287K miles....

 

Runs great, but last week my tach has been behaving erratically. It will jump around like crazy, regardless of how hard I'm revving the engine. In fact, with the engine off and the key in ACC position, it will jump around like crazy. But sometimes, it works fine.

 

I did some searching and it seems like there might be a loose connection somewhere... if I lightly tap the instrument cluster or dash, the tach will react.

 

I'd love it if someone could post a pic or give me explicit instructions of what to look for...

  • At the distributor (Isn't that where the tach connects?)
  • What should I be looking for at the fused connections at the battery (isn't that where it draws power?)

I really don't want to take apart the dash, is there a simpler way to get at the back-side connections?

 

This forum helped me (easily) fix my cruise control issue and I'm hoping for another win!

 

Thanks

 

-R

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Shouldn't take more than a Phillips to pull the gauge cluster, I think...at least that's how it is on my 04. Two screws for the bezel (slide your hand palm up above the cluster and you should feel the holes), and 4 for the cluster, in my case. Was similar for my Frontier, but I had to remove some lower plastic to see the lower screws.

 

I had issues with my Frontier cluster long ago...the printed circuit board ('sheet') had started to crack near the connectors...was causing the illumination to sometimes turn off half the bulbs (hitting the dash helped), but also caused the speedo needle to go flat (which interrupted the speed sensor signal to the ECU and threw some errors). Bought a replacement board from Nissan and everything fixed.

 

The new clusters use a rigid circuit board, so it's not an issue. But judging by the pictures in this auction, it uses the flexible circuit board. The white parts on the back are where the connectors go. Mine were cracked near these openings where the board flexes to make contact with the connect. The cracks were tiny, so look carefully.

 

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Ahh, you're right. Pretty easy to remove the instrument cluster. I took a look but didn't see anything obvious (no cracks or broken connections that I could see).

 

Any other ideas? Where are the connections made on the other end?

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Ahh, you're right. Pretty easy to remove the instrument cluster. I took a look but didn't see anything obvious (no cracks or broken connections that I could see).

 

Any other ideas? Where are the connections made on the other end?

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Well, worth a shot, I guess. Did you try wiggling any of the harnesses or wires while running? Wouldn't remove any while truck is ON. Are all the screws on the back snug?

 

As for the other wires...well, everywhere. The FSM should spell out specifically what wires to look for (color, pin position, connector type), how to test, and acceptable range (voltage, resistance, etc.).

 

If I were troubleshooting this, I'd be working a multimeter on the back of the gauge cluster and watching the voltage during revs (assuming the tach readout is voltage-based, which I'm sure it is). I'd first probe on the tach itself; If the readout increases with engine RPMs but the needle jumps or flatlines, then it's probably the gauge itself. Then, start working away from it: on the circuit board near tach, on the circuit board near the harness, and then on the harness. Keep working away from the tach. I believe the next point is the distributor (this is where I wired in a tachometer on my 1998 Frontier); the gauge cluster is between the distributor and ECU and I don't think there'd be any more connectors, except at the distributor, IIRC.

 

You can also try putting the multimeter in Ohm mode and check simple resistance between the points I mentioned above (may need to wiggle things...check for continuity first, then wiggle something to see if drops).

 

 

 

 

 

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