New tach sensor but still inaccurate reading.

[MtnHaul]

Installed a new Dorman tach sensor but my tach still won't go past 1800 rpm. What else do I need to check? And please don't say I need to chase the wires all through the harness and into the cab.

 

[Rdnck84_03]

Is it reading correctly up to 1800 and then just stops moving or is it reading slow through the entire range?

James

 

[MtnHaul]

I don't think it's accurate at all. When first installed it seemed to be reading correct at idle but after a few more starts it would sometimes read too low at idle and doesn't seem right at any engine speed. The old sensor had lost the jacket on a good chunk of the wires so I figured it was just 32yrs old and beat but I guess something else is going on. The old sensor behaved just about the same as the new one. It had worked fine for about 6 yrs and then just stopped reading accurately--no ideas as to why. It's a manual trans so tach is not needed but since I spent the money I would like it to work now,

 

[KansasIDI]

The parts store tach sensors have been absolute garbage in my experience. Only ones that seem to read accurately and last more than a few months are the OEM Ford ones, available online or from your local stealership.

The bullnose tachs get stuck sometimes, I remember reading somewhere about how to fix that, I think it was on FTE

 

[MtnHaul]

I don't know if the old sensor was oem as there were no visible markings. But the new Dorman unit behaves exactly the same so I suspect the problem is not the sensor. Today I was reminded that the tach will also sometimes decrease in RPM as I'm accelerating but this is not consistent behavior so I'm disinclined to think something is connected backwards.

 

[ROCK HARVEY]

On my truck, the flexible circuit board on the back of the gauge cluster is cracking and separating. First the fuel gauge went, and now the tach only works about half the time. If you have the same issue you can run a jumper wire to bypass the crack in the circuit board. While you have the gauge cluster out you can test the connector to see if the tach signal is making it to the gauge.

 

[WrenchWhore]

Mine would act funny when the tip got slightly covered with magnetic metal. I'd probably pull the cluster like @ROCK HARVEY suggested and just do some inspection and gently clean contacts.

Dumb question but is the sensor full seated in the aluminum housing?

 

[MtnHaul]

Mine would act funny when the tip got slightly covered with magnetic metal. I'd probably pull the cluster like @ROCK HARVEY suggested and just do some inspection and gently clean contacts.

Dumb question but is the sensor full seated in the aluminum housing?

Yeah it's fully seated. I suspect the cluster is at the heart of the problem since the new sensor really didn't change anything.

 

[MtnHaul]

Well I seem to have fixed my tach. While driving today I gave the gauge a nice five-finger-death-tap and voila! The RPMs seem to be accurate through the range now. I had tapped the gauge many times before but today I guess I had the magic touch.

 

[Kizer]

I had tapped the gauge many times before

Congratulations!
“58th time’s the charm”…what my Grandfather told me anyway.

 

[tbowker]

“58th time’s the charm”

I'm not so sure about that... it's called Heinz 57, not Heinz 58.

 

[Kizer]

I'm not so sure about that... it's called Heinz 57, not Heinz 58.

Perhaps Heinz 58 would have been better.?.

 

[tbowker]

Perhaps Heinz 58 would have been better.?.

Hmm, valid point. The world may never know since it seems they were content to rest on their laurels.