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hey my friend has 2 z-24's both '88s and they both have tachometer problems. they both read very high a lot. one of them will actually go off the guage most of the time.

what do u think it could be? is there a sending unit that could have gone bad. any ideas?
 

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I too have an '88 Cavalier Z24 with Digital Dash. The accuracy of my tach has gradually gotten worse. When I first recieved the car it seemed as though the tach showed it idling rather higher than it should have and it redlined easily. Now, a few years later, the tach shows it idling at around 3k - the needle is pegged about half the time I'm driving the car. It obviously responds to changes in engine RPM's but to a much greater extent than it should. Any simple solutions for this? Thanks.

Michael

PS - Great site. I've learned enough here and through a friend to actually feel comfortable working on my car.
 

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If your having trouble with the digital gauge cluster, there's not a whole lot than you can do yourself unless things have changed since my whole cluster went blank many years ago.

Most of the information going to your dash goes through the computer to the dash or through the dash to the computer. Some of the sensors on the motor feed the dash and the computer together. If the motor is not performing properly, then I would say to look at the sending units. But if the motor is fine, then the problem is in the cluster itself. The only sensor that provides this type of data is the crankshaft position sensor. If it was bad, the car wouldn't run.

I tried to get a schematic to the cluster some years ago when mine had an intermittent power problem (go over a bump and you had gauges, over another bump, everythings dark, except the analog tach). Since the cluster is considered an odometer, they won't sell the specs. I had to remove the cluster, extract the mileage chip, and the dealer sent it to some factory in Texas to be reconditioned.

Problem is, the car will run like crap without the cluster (Emergency Run Mode) and it takes up to two weeks to get the cluster back. I don't know if a speedometer shop may be a better way to go.
 

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I don't know about the digital clusters, however, in my factory service manual it has all sorts of tests and diagrams for troubleshooting these kinds of problems for the analog. I'm actually going to use one of them on X-mas day to troubleshoot my oil pressure guage.
 

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I did read something about this a while, but since I don't have the digital dash I just skimmed it, I beleive it was a resistor or a diode that goes bad over time, and once it is repleced everything works fine again.
 

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lets see on the coil packs theres a single wire lead to the tachometer, I used that wire to tap in a aftermarket gauge on my beretta...
I think that wire is voltage sensitive not frequency try and locate the wire (pink but im not sure) chilton's will tell you though, and mess with it a little to see if it corrects your problem could just be a corroded contact.

CPS if that wasnt functioning properly it would cause the car to not run at all, cuz it directly controls timing.
 

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I have a digital dash, tach was bad from day I got it. I took it out, made a face plate where it used to be with plexi-glass, cut a round hole in it and put in my own 2 5/8" tach. (I'll try to get a pic of this soon). I used the rpm wire comming to my remote starter, and it is connected to a wire in a large wiere pack (in loom) between the battery and firewall. I think it is purple and white ?, but I'd have to check to be sure.
 

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see im not sure either but hey if you want accuracy then i hope you never look at the dash for it, gm is horrible at accuracy with everything, hell my gas guage says half, and i got one mile and its boggin cuz its outta fuel. As for oil pressure, has three marks up, mechanical guage says 50 WTF!!!

So as you can see DOn't rely on GM's Gauges...
 

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gmarcott said:
Problem is, the car will run like crap without the cluster (Emergency Run Mode) and it takes up to two weeks to get the cluster back. I don't know if a speedometer shop may be a better way to go.
The car will run the same with or without the cluster. The computer's readings do not go through the cluster. I've run mine without any problems without the cluster.

There are people out there that can fix these dashes, but I think the best thing(and cheapest) to do is getting one from a junk yard. I've done both. I've never had a correct tach. The junker's tach was more off than my other one. The time it was fixed, they didn't calibrate it. Although, mine is consistantly incorrect. For example, when it says 7000 RPMs, it's really 4000. I just connected it to a scanner and compared.
 
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