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RPM Counter reading very high! Megajolt
Irony - 5/5/16 at 07:31 AM

I have a RV8 with megajolt and my RPM gauge is completely out. It was working ok and then when driving it flicks to some sort of wrong setting. Tickover is normally about 700-800 rpm and then it flicks up to 1400. The actual engine revs don't change. As the revs increase the RPM gauge gets progressively higher and more inaccurate. So when the engine is at about 2000rpm the gauge reads 4000rpm. When I attach a laptop to the car the megajolt output RPM is fine. Its a VDO gauge.

Any ideas?

40inches - 5/5/16 at 07:41 AM

So it reads about double the actual RPM? Can you not adjust the pulses from the Megajolt?
Is there a DIP switch on the Tacho?

britishtrident - 5/5/16 at 10:24 AM

Sounds like a bad connection causing spikes, check the connection and wiring to crank sensor (or distributor sensor) the fault could be internal to the sensor.

The other thing it could be is a spike from somewhere else on the car such as the alternator connections or a bad phase on the alternator.

russbost - 5/5/16 at 12:21 PM

quote:
Originally posted by 40inches
So it reads about double the actual RPM? Can you not adjust the pulses from the Megajolt?
Is there a DIP switch on the Tacho?


If it's reading accurately at idle then it's not going to be simply miss set, you don't say who's rev counter it is? Assuming that all connections are good & it's not picking up spikes from wiring being run close to HT leads or alternator, it probably just needs damping, a 1meg ohm resistor in series usually does the trick