Rev counter gone MENTAL ! ! !

[jsr]

Fitted Magnecor KV85 leads, Champion Eon plugs, Flamethrower coil, new distributor cap and rotor arm today. Fired the car up, only to find the needle on the rev counter bouncing around 1000rpm at idle, rather than a nice steady reading. It actually jumps by about +-500rpm or so. Blip the throttle, and it's even worse! It jumps around all over the place, even right off the dial!!!!

Under load (full throttle), the needle will give a good reading, but still moves around a fair bit. Something that i've fitted or done has caused the needle to lose it's damping or pick up interference from somewhere.

Could this be the leads? Incidently, my dad was watching TV and the moment the engine starting, the picture had a lot of interference in it.

Your thoughts would be much appreciated!

By the way, throttle response is greatly improved and a quick test on my data logger shows low down torque (>2600rpm) is increased dramatically. Just annoyed about the rev counter

>> Edited by jsr on Sunday 21st August 22:02

[petros]

My car was playing up and I've gone back to lucas leads, no probs.

[Cider Andy]

I'd suspect the coil.

[jsr]

I didn't say this in the first post, but the engine is completely smooth, it idles steadily and revs cleanly.

The rev counter seems to be indicating something completely different!!!

[harrow_chim]

Sounds like a HT suppression problem - I think the suppression resistors are built into the plug caps - have they been removed?

[jsr]

Suppression resistors? What should i be looking for?

[petea]

jsr said:

I didn't say this in the first post, but the engine is completely smooth, it idles steadily and revs cleanly. The rev counter seems to be indicating something completely different!!!

Mine is exactly the same...i am running with the rev counterbouncing all over the place on the basis that i know the engine sounds ok and as you say, the acceleration, etc is better.

Try changing the lead from the coil to the distributor back to your old one and see if it improves - mine did, but then i thought whats the point in having good spark from the dizzy when the delivery to it isn't as good?

Frustrating when you replace everything with recognised, quality bits!!

[ajcerb]

different car but when i had this on my cerb it was the Big Fuse cracking and on its way out - didn't know it at the time but afterwards was told it is a classic sign.

[hugerr]

I fitted a new Bosch coil and KV85 leads recently without any problems at all, so I think it safe to rule out those components at least.

Are you sure the lead taking the pulses to the rev counter wasn't damaged during the upgrade? Dirty connector, fractured wire, that kind of thing. Sounds like an intermottant connection kind of problem to me.

H

[griffter]

hugerr said:

I fitted a new Bosch coil and KV85 leads recently without any problems at all, so I think it safe to rule out those components at least. Are you sure the lead taking the pulses to the rev counter wasn't damaged during the upgrade? Dirty connector, fractured wire, that kind of thing. Sounds like an intermottant connection kind of problem to me. H

Ahh but you fitted the BOSCH coil. Flamethrowers (of which I have no personal experience) seem to be problematic with TVR V8s e.g. :

www.pistonheads.co.uk/gassing/topic.asp?t=198177&f=8&h=0&p=1

It seems the LT wire to the rev counter is picking up intereference. Change the coil back - see if that cures it. If not, try the leads.

[mark tvr-loud]

Had a similar problem too. Replaced the leads with nice shiney 10mm racing leads rather than the ropey old ones I was running on. Car seemed more responsive for sure but the rev counter was all over the place on tick-over. The tickover isn't particularly smooth on my car anyway but certainly not as jumpy as the rev counter was suggesting!!

Swapped the Coil to Distributer lead back to the old one and hey presto...all ok.
Doh! Been running on this combination ever since as all is ok but seems a shame to have new leads all round except for probably the most important one!

So if it is a suppression issue, is this due to a faulty lead??

Mark.

[the dodger]

Same as you jsr. Fitted magnecores, new shields, new bosch coil, dizzy cap & rotor arm 2 yrs ago. Tacho boucing about - actually increases (by about 500rpm) when you lift off. Went back to the old (good) coil - no difference. Not going to change anything else back - living with the bouncy tacho! Wahey!

[jsr]

Yeah, i can live with the bouncy needle. With the exception of the Flamethrower coil which i think causes a slight stutter at 3000rpm ish (it's hard to tell now ), the car is driving really well.

Up to about 2600rpm, torque has increased by up to 25% according to my data logger