Tachometer is very inaccurate

[Sn8kebitten]

I’ve had a suspicion for awhile now that my tachometer has been reading off since buying my Cobra back last year. It never felt or sounded the same during WOT like I remembered from 10 years ago. At 70mph with 4.10s, it reads around 3400rpms and even with those gears, that seemed higher than I remember. So I hooked my SCT X4 I have from my other car up to it, and if I hold the gas at what the cluster says is 3000rpms, the tuner only shows 2493rpms. While held at 4000rpms, it showed 3320rpms. Any ideas where I should start to finding the problem? Or should I just try to find a used cluster to swap into it?

 

[Blowncobra_97]

https://www.cjponyparts.com/speedometer-driven-gear-kit-type-3-17-18-20-21-tooth-mustang-with-automatic-manual-transmission-1965-1998/p/SGK1/?msclkid=06365491241018489a6a32a2541a7868

 

[96dreamer]

Is it possible the needle on the tach was removed at some point? I had to remove mine a while back and it is still ever so slightly off.

 

[venom1997]

It’s crazy I don’t even look at my cluster gauges anymore run a scan gauge 2 Velcro to my dash above the steering column I have it set to read rpm mph iat and water temp it’s easier to view a digital gauge set. However my analog tach is spot on with the ecm rpm I wonder what could cause that other than the needle has been moved at one point by hand. Mwolson would know paging Mwolson


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[Black Gold 380R]

Is it possible the needle on the tach was removed at some point? I had to remove mine a while back and it is still ever so slightly off.

Yep, they are white face gauges. So, I would assume the needle was removed during that installation and installed incorrectly. That's my guess anyway.

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[Blkkbgt]

Yep, they are white face gauges. So, I would assume the needle was removed during that installation and installed incorrectly. That's my guess anyway.

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Most likely this!

I would pull the needle and simply put it back on. See if the spindle turns at all when you remove it.

 

[Sn8kebitten]

Is it possible the needle on the tach was removed at some point? I had to remove mine a while back and it is still ever so slightly off.

Now that you mention it, the middle of the 3 owners that had it after I sold it did install LED bulbs in the the cluster, so maybe he removed it? Definitely something to look into though.

Yep, they are white face gauges. So, I would assume the needle was removed during that installation and installed incorrectly. That's my guess anyway.

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As far as I know, all Cobras had white face gauges OEM, I don’t think this one has ever been changed, just the bulbs in the back. But it would be great if that turns out to be the problem

 

[Sn8kebitten]

Finally got around to pulling the cluster out of the dash. Is removing the tach needle as simple as pulling up on it? I’ve pulled gently but I don’t want to break it

Edit: Well I read about using a fork to gently pry it off, so that’s what popped it off. I went ahead and installed the cluster back in the car and cranked it, then connected my X4 handheld and did a datalog to watch the needle, and it was still off.

So I pulled the needle back off and watched the X4 rpms show around 900, then I pushed the needle back into place there and that kept it accurate up to 1000rpms. But anytime I rev the engine, the X4 would show 2000rpms while the needle would jump to 2400. So I pulled the needle off again, held the throttle at the X4s reading of 2000, then pushed it into that position, but then when the rpms drop to 900 on the X4, the needle will drop all the way to 400rpms or so.

So no matter where I manually put it at the correct spot at, it’ll be off on the opposite end of the gauge. So I guess the gauge is just bad

 

[I_like_turtlez]

What's the mileage on the vehicle body/cluster?

If I remember right these are still analogue gear driven gauges, didn't go digital clusters until 99+ unfortunately(so many fake mileage cars out there)

If it's a high-mileage car I suppose the plastic gears could have worn but I would be looking at the throttle cable/TPS first because immediately it looks like it's either not opening all the way or the PCM is confused

Hopefully you can find the Ford re-calibration procedure for that tach, pulling off needles is a big no-no

 

[Sn8kebitten]

What's the mileage on the vehicle body/cluster?

If I remember right these are still analogue gear driven gauges, didn't go digital clusters until 99+ unfortunately(so many fake mileage cars out there)

If it's a high-mileage car I suppose the plastic gears could have worn but I would be looking at the throttle cable/TPS first because immediately it looks like it's either not opening all the way or the PCM is confused

Hopefully you can find the Ford re-calibration procedure for that tach, pulling off needles is a big no-no

The car has 171,000 miles