Intermittent Rev counter flutter/stop

[Markharrison2]

I have twice had drives where the Rev counter flutters and drops under constant acceleration. But the next time I come to use it, it's fine. Both were hot ish days. 20c is hot in scotland! After the first time I took the dial out and tried to check the electrical supply with a multimeter, have to be honest didn't really know what I was doing, eventually found a wire going in with power but it only read 5v iirc. And then it was fixed next time I took it out. It has had an aces Shift light system fitted too, but that doesn't seem to be affected, although it would be a little harder to tell with that.

can anyone help me with what I need to do to establish the cause of the problem. Does it need a new Rev counter?

thanks

[Jonathan Kay]

Any other instruments affected?

Do you have a wiring diagram?

What ECU or ignition system?

When were the shift lights fitted?

Jonathan

[Markharrison2]

No other instruments affected.

emerald k3 ecu

there seems to be wiring diagrams in the back of the assembly guide. Can try put it on here if that helps?

it is a 2006 1.8 k-series. 

The aces sure shift 2 was fitted 2008

thanks

[Markharrison2]

So interestingly I had the heater on when this happened. On the last drive I pulled over after it was happening. Turned off the heater and it didn't happen again. On the wiring diagram the tachometer is next to the heater fan. There is also a diagram for the tachometer plug, so I should be able to work out if any of those inputs are at fault...

[Jonathan Kay]

Exactly.

Not sure how the fan could be related if it isn't blowing any fuses and other instruments aren't affected.

As usual with intermittent faults this may not be easy.

1. Identify the earth, power and signal leads at the instrument. Ignore the instrument illumination. Check that voltage again on the power lead with the ignition on. If it isn't the same as the battery voltage disconnect it from the instrument and check again.
2. Trace those wires back to their other ends, and through the loom connector if relevant.
3. While it's running give them all a wiggle wherever they are accessible and see if you can reproduce the fault.
4. Check all the wires are well connected to all the connectors and all the connectors are tight on the instrument and at the other ends. 
5. Find the instrument earth to the chassis. Disconnect, clean and replace. (This is an unlikely cause as the other instruments aren't affected.)

Jonathan

[Markharrison2]

Thanks for the advice Johnathan, will do some investigation. Seems like other people have similar faults from another thread next to this one, your approach sounds worth a shot, thanks

[garybee]

Do you have access to a multimeter with a frequency counter function?  If so you could bodge it to the dash and run it in paralel with the tacho'.  When tacho' drops out, check multimeter to see it it's still reading.  You'll have a definitive answer that way.

[Markharrison2]

My draper dmm1a does not appear to have a frequency counter function unfortunately. Good idea though, might see if I can borrow one. Thanks

[Markharrison2]

Ok just spent an hour in the garage. Traced the earth back from tacho. Came across a big lump covered in electrical tape, decided to unwind it and found the loosest electrical connection I would ever want to see. Fixed that, and did a garage test, problem did not reoccur. Time will tell.

i did notice the aces shift light reads a slightly lower rpm than the tacho indicates. Is this common?

thanks for the helpful suggestions

[Jonathan Kay]

I was just about to ask: Saturday evening seemed like a good time. :-)

That could be from a previous abortive attempt at wiring the shift lights.

i did notice the aces shift light reads a slightly lower rpm than the tacho indicates. Is this common?

There are known issues about getting the right settings for the number of cylinders and ignition system, but I haven't heard of small factors, rather than eg 2:1. IIRC the factory fitted ones need to go back to be tweaked but the aftermarket ones are DIY.

Jonathan

[Markharrison2]

Ok, well I won't worry about the small difference in rpm between tacho and aces. It is roughly max of 1.2:1 so not too big a deal.

cheers

[Mankee]

You can hook up the Emerald to a laptop and see what the revs from the diagnostics data are like compared to the tacho and ACES lights. The Emerald also has a tacho signal multiplier function, if your tacho and shift lights take their feed from the ECU and not a coil.