Mad Revcounter
Discussion
Hi ,
The latest brainteaser my car has come up with is strange.
When I start the car from cold the revcounter behaves.When the car has warmed up for about a minute the revcounter then flys round off the scale.
The engine revs are normal and the car is an SE chargecooled with the vdo type gauges .
I am sure its simple but I,ve tried everything I can think of.
Also my hazarrds have just packed up but the indicators still work...dOH!
HELP Pleeese!
Richard
86 Turbo
92 ChARGECOOLED
The latest brainteaser my car has come up with is strange.
When I start the car from cold the revcounter behaves.When the car has warmed up for about a minute the revcounter then flys round off the scale.
The engine revs are normal and the car is an SE chargecooled with the vdo type gauges .
I am sure its simple but I,ve tried everything I can think of.
Also my hazarrds have just packed up but the indicators still work...dOH!
HELP Pleeese!
Richard
86 Turbo
92 ChARGECOOLED
It's pretty difficult to know without investigation. If you asked me to hazard a guess then I'd offer the following, but that doesn't preclude any practical knowledge that others may have.
Electronic rev counters, usually count pulses. If yours is of this type, then there will be a gearwheel somewhere, probably the flywheel, and a sensor that detects the teeth of the gear passing it. Obviously as the teeth go past the sensor you get pulses, and the faster the engine the more pulses you get. The revcounter then just indicates the pulse rate, which is an indication of engine speed.
If it's temperature related then, it's really must be something to do with the engine. The thing to think about is that the pulse sensor is probably transistor based (amplified), to get a good signal from the sensor along the cable back to the rev counter.
If your rev counter is counting more pulses than it should, then there's probably a noise problem. Amplifiers often fail noisily, if you could hear it, it would probably be crackly, rather than a monotonic drone. They can also partially fail, where they work normally when cold, and poorly when hot.
As I say I'm hazarding a guess, but I'd say that the sensor is knackered. I'm assuming that the amplifier is the actual failure, but they're often packaged up in the body of the sensor.
The only way to tell for sure is to put an oscilloscope on the sensor output.
If it's a mechanical rev counter, none of the above can be true.
Electronic rev counters, usually count pulses. If yours is of this type, then there will be a gearwheel somewhere, probably the flywheel, and a sensor that detects the teeth of the gear passing it. Obviously as the teeth go past the sensor you get pulses, and the faster the engine the more pulses you get. The revcounter then just indicates the pulse rate, which is an indication of engine speed.
If it's temperature related then, it's really must be something to do with the engine. The thing to think about is that the pulse sensor is probably transistor based (amplified), to get a good signal from the sensor along the cable back to the rev counter.
If your rev counter is counting more pulses than it should, then there's probably a noise problem. Amplifiers often fail noisily, if you could hear it, it would probably be crackly, rather than a monotonic drone. They can also partially fail, where they work normally when cold, and poorly when hot.
As I say I'm hazarding a guess, but I'd say that the sensor is knackered. I'm assuming that the amplifier is the actual failure, but they're often packaged up in the body of the sensor.
The only way to tell for sure is to put an oscilloscope on the sensor output.
If it's a mechanical rev counter, none of the above can be true.
Hi again,
got the car back and now as I turn the ignition on the revcounter just shoots round to max before the engine is started.It does move back slightly if certain things are switched on i.e the hazards or lights!!!
I,m told that the se doesnt have a voltage stabiliser but that it may be caused by the rpm plug in the boot??
I dont really want to take the dash pod off if its an easy fix but as everything else works i am leaning toewards the revcounter being broken.
Surely someone else has had this problem!
The car seems to run ok otherwise although the idle can be a little high on start up.
Rich
got the car back and now as I turn the ignition on the revcounter just shoots round to max before the engine is started.It does move back slightly if certain things are switched on i.e the hazards or lights!!!
I,m told that the se doesnt have a voltage stabiliser but that it may be caused by the rpm plug in the boot??
I dont really want to take the dash pod off if its an easy fix but as everything else works i am leaning toewards the revcounter being broken.
Surely someone else has had this problem!
The car seems to run ok otherwise although the idle can be a little high on start up.
Rich
Thanks,
I must admit the problem seems to have occurred after a rather energetic jetwashing session.
I have stripped a lot of the car down today to do a full service and check all the earths in the engine bay so I,ll see if that helps.
Howwould I groud therev counter withou emoving te binnacle..is it nough to attach an earth to the bezel?
Thanks for your help.
Rich
I must admit the problem seems to have occurred after a rather energetic jetwashing session.
I have stripped a lot of the car down today to do a full service and check all the earths in the engine bay so I,ll see if that helps.
Howwould I groud therev counter withou emoving te binnacle..is it nough to attach an earth to the bezel?
Thanks for your help.
Rich
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