Rev counter peculiarities

[pepperish]

Hi,

I have just bought myself an 8v - lovely car but I do have a slight issue with the rev counter.

I've spent the last few days searching existing topics on this but have yet to come up with a solution. My rev counter seems to work but when the engine is idling, it will sit just about 0rpm, not at 800rpm. If I rev the engine, the needle will move up as per usual.

I've checked the earth connections and the red/black wire from the coil. When I pull fuse 21 the engine dies, but the rev counter then moves up to its normal idling position, around 800rpm.

Any ideas? And apologies for bringing up another rev counter thread!

Thanks.

[rubjonny]

where is the hazard switch, dash or column?

[pepperish]

Hazard is on the column. It's a '91 car and has motometer clocks.

Should the engine die when pulling fuse 21?! It has an aftermarket immobiliser installed and I'm wondering if they've spliced it into something else which is affecting the voltage at the clocks from the coil??

Complete stab in the dark!!

[rubjonny]

yeah that'll explain it, 21 fuse should have no effect on the engien at all. still doesnt explain the rev counter issue! maybe pull dash fuse for 30 seconds and see if that helps. otherwise i think you'll need some new clocks, cant think of anythign else which would make it almost work but not quite 

[pepperish]

Ok thanks. Dash out time me thinks...

[rubjonny]

sorry what i meant was the immob is probably spliced into a feed on fuse 21, in case it wasnt clear

[pepperish]

Yep, fuse 21 is also the feed for the rev counter and MFA though isn't it? Hence, if they've spliced in to it, it may be causing the problems with the rev counter??

[rubjonny]

no its not specifically for the rev counter, just power for the clocks. revo comes from the -ve terminal on the coil, its the red/black wire. worth a look there but as i say if wiring bad it would just not work, cant think how it would do the odd things you are seeing? unless the immob is spliced into it for some other reason like remote start or something, and is causing issues...

[pepperish]

Ok, think i'll take the dash out over the next few days.

I'll update this thread just in case anyone else if having similar issues.

Thanks for your help 

[pepperish]

Ok, I disconnected the battery for an hour this morning then reconnected and started her up - voila! Fixed, I thought....

Took it for a quick drive and after about 10 mins it was doing the same thing again. At idle, needle sits at about 200 rpm.

Disconnected the battery again, reconnected it and same thing again. Fine at first but after 10 mins it starts playing up.

Is it time for new clocks?!