Tapping noise.....??

[Mad Mitch]

In last couple of days a strange tap/knock has appeared. It seems to be coming from the o/s head towards the front OR the plenum....Thought at first it was one of the leads/shrouds shorting out as that is the type of noise but all seems ok with them... The only other symptom is that it now idles very poorly from cold, surging to the point of almost stalling untill it has run for a couple of mins..Had the stepper motor out several times and cleaned it. It has never ticked over smoothly when warm but never a problem... Temp switch changed and plugs,cap,rotor,leads all done last year due to a sooting up problem/misfire which is sorted.... All help greatly appreciated.
Steve.

[dlewis]

Symptom 1 could be an exhaust gasket but this may not solve the idling.

Take a lead off the O/S cylinders in turn and see if the noise continues.

Symptom 2 check and swap the plugs in this bank.

Look for air leaks.

Dave

[Cider Andy]

Exhaust gasket sounds favourite to me too, but that wouldn't necessarily explain a new desire to stall. I wouldn't advise running the car with a plug lead removed: it has the potential to cause serious injury but it can also damage the ignition system.

[Mad Mitch]

Cheers for the replies guys..... It is not a manifold gasket. Wrong type of noise completely..... Dont think it is plug related either although removing each lead in order will eliminate little ends etc..If you imagine the noise a plug lead makes when held away from the plug but still firing the plug that is the type of noise it is making, a hollow tap/knock...... Not heavy enough a noise for a worn cam lobe. Has there been any issues with the trumpets under the plenum ??? Could one of them be rattling ??

[dlewis]

Could you have a break in the new leads - more noticeable at low rpm?

You could meter them or swap.

[GreenV8S]

I would guess an exhaust gasket leak or crack in the exhaust, making a tapping noise and also allowing air into the exhaust and leading to over-fuelling and a lumpy idle.

[Mad Mitch]

Had a look under the bonett this morning in the dark and there were no signs of a lead shorting out/ blue flashes etc......
GreenV8.... The noise appears to be higher up than the manifold although what you say makes sense.... The noise just does not sound like an exhaust/manifold blow.

[Mad Mitch]

Thats a possibility..... Not bad to check either at a guess ??

[GreenV8S]

Mad Mitch said:

The noise just does not sound like an exhaust/manifold blow.

You're there I'm not, but a leaking exhaust manifold does have a very mechanical knock to the sound and not at all like the classic puttering sound of a leak further down the exhaust system.

Edited by GreenV8S on Saturday 21st October 14:20

[Nick P]

GreenV8S said:

Mad Mitch said:

The noise just does not sound like an exhaust/manifold blow.

You're there I'm not, but a leaking exhaust manifold does have a very mechanical knock to the sound and not at all like the classic puttering sound of a leak further down the exhaust system.

Edited by GreenV8S on Saturday 21st October 14:20

I'm pretty sure mine is doing it as well (thread the other day)....is it a hard job to do, or should i just throw it at the mechanic next time i get it serviced?

[shadowninja]

check stones haven't got stuck in that belt. also it develops hard spots which tap, so might be worth replacing it.

[Cider Andy]

Nick P said:

I'm pretty sure mine is doing it as well (thread the other day)....is it a hard job to do, or should i just throw it at the mechanic next time i get it serviced?

Much easier to give to your mechanic. The job is not very involved but lack of space in the engine bay makes it very awkward.