REV COUNTER OVERSTATING BY APPROX 1200/1400 REVS...

[mrgrumpy2]

I went to the marina this morning to start the boat and much to my suprise the rev counter (which has never missed a beat previously) was reading 2000 RPM when the engine was on tic over at approx 600/700 Revs. It then continued to overstate the RPM whenever I reved the engine. Its a 1999 Searay 260 Sundancer which has a Mercruiser 5.0 Thunderbolt engine. Is the problem likely to be the pick-up, the cable or the head unit on the dash? Is it potentially fixable or will something have to be replaced. It has been extremely cold of late and I'm wondering if that may have played a part. Thanks in advance for your comments.

 

[spannerman]

A friend had the same fault on the same boat, it was caused by a misfire. Does the engine run normally? If so then check all the connections, the rev counter gets its signal from a grey wire on the coil negative terminal, check the connection, also check the engine harness connector and the ignition module earth and the rev counter for 12v supply and a good earth, if these are OK then ultimately its the rev counter.

 

[Duster]

Mine did just the same on a Merc engine at the start of last season. I contacted a friend who is a Merc specialist - he said "common problem when they have be standing some time - thump the dial with your hand!" - I did and sure enough it fell back to the correct reading. I rang back and thanked him.
Next day I received a joke invoice for £50.05 - 5p for hitting it - £50 for knowing what to hit.
Seriuosely try it with the engine running - it is probably a poor contact.
Regards mikej