Rad cooling fan tripping in causes Rev counter to blip by 3000 revs

[jellytott]

944S 1988 non AirCon and single fan.

Before I starting investigating this issue from scratch has anyone encountered this problem before ?
Whenever the cooling fan trips in it briefly causes the Rev counter to blip and increase by 2000-3000 rev's then it returns to normal, also it kill the power to radio too as it turns off and on quickly.
Initially, I thought a loose power feed to the radio but today noticed it blips the rev counter too which is more of a worry, my early thoughts is earthing when the initial kick of volts from the fan cuts in its back feeding to earth via the radio and instrument cluster earths?

What earths studs I have seen look good but thats not to say it is one of these little rascals somewhere, any idea's as always will be much appreciated.

Many thanks

John

 

[John Sims]

You have come to exactly the same conclusion I had. I've not experienced it on a 944 but my wife's old Land Rover is very prone to bad earth faults.

My only other thought is it could be a problem with the voltage regulator but bad earth seems the more obvious.

 

[jellytott]

Thanks John,
Yes I'll leave it a while hopefully someone has the answer otherwise in some respects this sort of problem is a pain to chase and fix.

John

 

[zcacogp]

Bad earths is my thought as well.

You could remove and clean up all the earth points in the area (and there is a good list of them in the workshop manuals). However a quicker and easier way is to find the earth wire in the loom, splice into it and make a new earth somewhere on the bodywork. I'm not sure that I can recommend this, both on a 944 and in the engine bay, but it worked well with bad earths on Mk1 Golfs in the dashboard loom. Making a new earth point on a dashboard bracket was a simple job and solved a lot of time.

Oli.