Antrooper

Hi! i have a 1998 V6 firebird, and well its having speedometer issues. its giving me an inaccurate speed reading, about 15 or so above the correct speed. I have replaced the speed sensor, and i have checked all the wheel speed sensors(The ABS light wasn't on, but when i unplugged the wheel sensors then turn it over it would come on) The check engine light is not on, so i have no clue what else to check. my guess is the instrument cluster itself. id love to hear what you all think.

-Ant

wssix99

iTrader: (5)

Is this car new to you? Has it always done this?

Antrooper

Yes i bought this car in December or so, and it had speedometer issues then, and still does now.

bammax

Putting the v8 cluster in a v6 car will give you an inaccurate reading on the speedo and tach. People do it for looks without knowing the issues.

Antrooper

How can i tell if its a V8 cluster vs a V6? could the problem also occur if its a Camaro Cluster too?

wssix99

iTrader: (5)

Test the odometer. If it's off to the degree of the speedometer, you have the seller over a barrel. (It would be illegal for them to sell you a car with an incorrect odometer. I expect this would be the case if you have the wrong cluster in the car. If you don't have the original cluster in the car - there should have been paperwork for that also!!!)

Can you check the speed with GPS? Is the needle off always by the same amount? Or does the difference change? Does the cluster have the original gauge face on it, or has someone put a decorative one on?

Nathan C

A 150 mph Speedomotor is a v8 and 120 is a v6.

Antrooper

Its a 120 Speedo Gauge. How would i test the Odometer exactly? There was no documented paperwork about the speedometer/odometer being changed, but there are signs that show the instrument cluster was removed at one point in time. It has about 150,000 miles on it at, and no it does not have a decorative gauge face. its about half of the actual reading. E.x if its going 40 the speedometer is reading 80, if its going 20 the speedometer is reading 40.

wssix99

iTrader: (5)

No worry about testing the ODO if you have a V6 gauge set. (Testing it would be just to drive 10 miles and see if 10 miles actually click off...) If you have a V6 cluster, it should be fine.

Did you get an assertion that the odometer reading is correct? (ie: that no one tried to roll it back)


That's odd. Sometimes people will move the needle on the post, but that will always show off by the same amount. I would think that being off by a ratio would point to something electrical.

The next thing I would check is to hook up an OBD II scanner with live data and see if the PCM reports a correct speed. (ie: are the sensors correct and do you just have a guage problem?) Maybe the gauges were removed because the previous owner was chasing the same ghost?

Antrooper

Could be, but I am going to try and change the gauge cluster to see if that fixes the problem. if not then ill have to buy a OBD II scanner, and look at the live feed. i don't think anyone has tried to roll it back, but i cant be positive. all test the ODO just in case. Other than that the only thing i could really think of is damaged wiring.

seawolf18

iTrader: (18)

Do you have different size tires, other than factory? That will also throw your speedo off.

wssix99

iTrader: (5)

No can do. The cluster is electronically matched to the car. (So people can't swap them out to get a lower odometer reading.) If we could do that, clusters with low odometers would be a very valuable commodity!

It is possible to swap clusters, bit one has to do that with a certified technician who can match the cluster to the VIN, correct the odometer, and supply the paperwork to go with the car's title for the action. You may still need to do this but given the expense, it should be a last resort.

You should be able to get inexpensive scanners now, which show the real time data, (if you don't wan to invest in a full-featured scanner or software) which connect to your phone via bluetooth.

JohnnyBs98WS6Rag

iTrader: (1)

Isn't the speedo calibration adjustable with a programmer? I know when I installed my HPP3 on my '98 years ago, I had the option to select a different gear ratio and tire height so that my speedo would remain accurate. I assume the PCM in the V6 cars have the same capability, no?

fst100

iTrader: (5)

thats what I'm thinking too. what size wheels and tires are on there right now?

WhiteBird00

iTrader: (4)

It would take some pretty impressive wheels/tires to make that kind of difference. Even going from stock 215/60-16 to something much larger like 275/50-20 only makes a 17% difference and he's talking about doubling the reading.

RockinWs6

That's not true, you can swap it vin isn't in the cluster.

wssix99

iTrader: (5)

What is true then? Obviously you have some advanced knowledge on the subject. Why are you keeping it to yourself?

Antrooper

it has 16s. Im pretty sure it still has the stock wheels. Im not sure you can re-calibrate it with a programmer, maybe you can, but i wouldn't know for sure. i had contacted a Buick dealer(they used to be a Pontiac dealer, and worked on them all the time) and they couldn't really tell me anything besides changing the rims/tires. i have no clue what to do from this point. i guess ill just have to hook up an OBD II scanner, and try looking at the live data.

bammax

https://ls1tech.com/forums/pcm-diagn...e-cluster.html
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Antrooper

so do you think i should get a new cluster? or should i run an OBD II scanner?