5 replies to this topic

[Elfie]

Right, I have an issue. I've just noticed it the past week or so.
I've just been to pick my girlfriend up from the station, on the way there doing 70 my revs were about 3600, idle was 1000
On the way back, at 70 the gague was reading 4500, idle, about 1500 and the revs and speed weren't going up evenly. However, sat at 70, the engine was definatley not doing 4500rpm, I could hear that, and when I just blipped the choke and the revs went up then fell sharply, they went down to just below 1000 but the engine was obviously at lower revs.
Is it possible that the rev counter could read more than the engine is actually doing? The clutch certainly doesnt feel as if it's slipping when accelerating, I still have plenty of acceleration in 4th etc.

Thanks very much,
Ben

[Elfie]

Anyone?

[998dave]

You got a missfire?

4,500 - 3,400 would be one lost cylinder.
1000 - 750 would be one lost cylinder.

If the rev counter is working using the spark from the coil then a missfire could cause this. How is your dizzy? and plugs? Doubt it'll be leads as they'd be earthing rather then missing.

D

[Elfie]

It normally sits at the lower rev reading on the gague. It's useful to know that the gauge reads from spark from the coil.
What would a 998 normally rev at at 70? Mine has sat at ~3600rpm for the past year, just confused as to why suddenly everything is giving higher readings now. When accelerating and stuff where i would normally change gear using how the engine sounds and the speedo the rev counter is saying it's ~1000rpm higher, even though the sound and the speed are as normal.
I've done the clutch slip test and it stalled, so I guess that's not the cause. I'd just rather the rev counter be accurate

Thanks,
Ben

[998dave]

"Sometimes" they work of the negative of the coil, you'd have to check yours...

There was a rev/speed calculator, and it depends a lot on Final Drive Ratio, I knew it for my Mayfair once upon a time, checked with the old timing light, but can't remember now, and the Hornet/Elf is bound to have different ratio's or FDR.

Can you get hold of a timing light with digital readout, may be best to check ur rev counter against the pickup from a timing light, see if it's the engine, or 'just' the rev counter...

[Elfie]

I am assuming that the rev counter is malfunctioning. The car it's happening in is a mayfair. All I know is that last week, before the MOT, the idle was just under 1000, sounding fine, sat at 70 at 3600rpm, sounded fine, now my idle is 1500, sounding as it did before, sat at 70, revs read 4500rpm, engine sounded like it did before at 70.
Does anyone have an suggestions of how to fix this? I'm 90% sure it's not a slipping clutch as the car pulls fine in all gears and the handbrake on/4th gear test suggested no clutch slip.
Mabye a cog in the back of the gague has slipped a tooth or something