Strange fault

[stuieg]

Firstly, a happy new year to all on Pistonheads.

Now then, the Griff has developed an odd fault and I was wondering if anyone could help me out with it.
The engine seems to have a power reduction, almost like the rev limiter cutting in, under acceleration. I did a road test today and noticed that this power reduction is RPM dependent regardless of which gear I'm in. The engine loses power abruptly at about 4900 RPM and if I release the thottle a little and let the RPM fall it cuts back in about 4500 RPM. It's the same in every gear. The engine is running fine in all other respects.
Any ideas?

[jimbro1000]

Not saying it *is* the problem but in similar situations on other cars I've had it turned out to be the coil

[crankedup]

Is this fault apparent when the engine is cold or only when hot, or makes no difference. ?

[Guillotine]

sounds like ignition to me.

could be fuel pressure

unlikely to be air if its not load dependant

good luck

[v8 racing]

My guess is the rotor arm! try and locate a genuine lucus one

[shpub]

That is suspiciously around the point when the vacuum advance starts to work. The advance unit can come loose and then it moves rather than advancing the ignition. It is bolted to the dizzy body by a couple of screws.

[stuieg]

It only seems to do it when the engine is hot but then again I don't accelerate hard until the engine warms up. I have a spare coil so I'll try that tomorrow. Checked the vacuum advance today and all seems ok.

[starmist]

v8 racing said:

My guess is the rotor arm! try and locate a genuine lucus one

It's amazing how many 'faults' there can be when the rotor arm is faulty. I had no end of problems with mine for months - it gradually deteriorated. It was lumpy, wouldn't tick over when cold, seemed like the plugs were fouled, faulty leads, fuelling problems, until the thing finally broke, and after replacing it, all my troubles seemed so far away.....

[dai capp]

I had a similar problem and it turned out to be the vacuum advance that had come adrift. There were one or two other problems apparent such as rough running but it all cleared once the vac advance was re-attached.

Cheers

DC

[stuieg]

But if it was the rotor arm (which looks ok) would the fault be so RPM specific. The vacuum advance unit is also secure. How could the vacuum advance be tested? Still not yet tried the coil as it is a fairly new one.

[siwes]

It is the coil amplifier breaking down
simon