Weird (& unwanted) pops and bangs from the engine

[Yellow Griff]

Hi folks,

as the topic says I'm getting some weird pops and bangs that sound to be coming from the engine/exhaust/manifolds on my 97 Griff.

It only occurs under hard acceleration with the engine under load, e.g. 3rd gear overtakes once you reach about 4000 rpm. I then get fairly loud bangs every 1/2 sec or so until I change gear and the revs drop. Happens all the time so can be easily repeated.

Doesn't occur under "normal" acceleration and doesn't occur in the drive or on a ramp.

Have taken it to a local specialist who are now scratching their heads. They say it doesn't sound terminal (they're confident its safe to drive) and it doesn't sound like a normal misfire, pinking or detonation problem. We put it on a rolling road so we could re-create the problem with the car static and are still none the wiser. They've throughly checked over the car and are confident that nothing is loose or broken externally.

Its going back in again after BNG for a couple of days so they can have a good look and fiddle with a few things. Any pointers?

Thanks,

Simon

[stesrg]

Yellow Griff said:

Hi folks, as the topic says I'm getting some weird pops and bangs that sound to be coming from the engine/exhaust/manifolds on my 97 Griff. It only occurs under hard acceleration with the engine under load, e.g. 3rd gear overtakes once you reach about 4000 rpm. I then get fairly loud bangs every 1/2 sec or so until I change gear and the revs drop. Happens all the time so can be easily repeated. Doesn't occur under "normal" acceleration and doesn't occur in the drive or on a ramp. Have taken it to a local specialist who are now scratching their heads. They say it doesn't sound terminal (they're confident its safe to drive) and it doesn't sound like a normal misfire, pinking or detonation problem. We put it on a rolling road so we could re-create the problem with the car static and are still none the wiser. They've throughly checked over the car and are confident that nothing is loose or broken externally. Its going back in again after BNG for a couple of days so they can have a good look and fiddle with a few things. Any pointers? Thanks, Simon

Hmm I was getting pops and bangs and nice flames comming out the back of the exhausts, was a knakered manifold sucking in a little air to aid combustion was good though
Ste.. edited because twas wrong doh..

>> Edited by stesrg on Saturday 3rd September 21:38

[seasider]

v8 racing said:

What happened Saturday? Was hoping to see you...

[GreenV8S]

The two obvious candidates are a misfire, and an air leak in the exhaust (sucking in air and allowing excess fuel to ignite). A leak in the exhaust would have more effect at light throttle especally on a trailing throttle and doesn't fit these symptoms. Sounds to me more like you have a misfire at high revs/full throttle. This is the sort of thing a weak spark could cause so a check of the ignition system would be in order.

[SteveGRF]

Yellow

This happened to a Chevy Engine I used to run, turned out to be a droped cam follower. Worth removing the rockers just to have a quick check for damaged followers etc.

Steve

[Yellow Griff]

Thanks all,

off to BNG now and then take it in to be checked on Wednesday.

Simon

[Yellow Griff]

OK All,

here's an update on the problem.

Firstly one of the exhaust manifold gaskets was just starting to blow - not massively but enough to let some air in.

Secondly the distributor cap and rotor arm were just showing signs of wear and starting to break down.

Individually not a problem but collectively certainly not helping. After fixing those the popping and banging was still there, but now with a different note/tone.

Further investigation suggests that there is a problem with the inlet valve on no.4 cylinder. They reckon its not too major and is probably just sticking, but until the head comes off we won't know for sure. [Need a "fingers crossed" smiley]

Anyway, whilst the heads are off is there anything else I ought to get checked out and/or upgraded?

Thanks,

Simon

[red griff 500]

Hey stevegrf, how do you check cam followers by removing rockers?

[SteveGRF]

Oops

I meant remove the rocker covers & visual check the rockers for signs of damage, excessive wear etc

Steve