Is pinking usually worse at higher revs?

[brogenville]

Having had to make up a set of fuel rails from scratch, I've finally got round to firing up my new 4.5 engine. The old girl fired up straight away, and much to my relief, the home made rails seem to be working safe and well. The only real problem Ive had though is an intermittent knocking noise with the engine on idle. Its single knock that occurs every 20-120 seconds. Sounds a bit like a toffe hammer being tapped against a cam cover. Thing is it seems to go away when the revs are raised up a bit (3000 or so). The engine map I'm using is just the standard 4.2 map- just being used to start the engine and run it in the garage until I sort out a proper map.

Could this be pre-detonation, as I thought that was more of a worry at high rpm's?

Then again, the AJP ecu advances the ignition on idle (doesn't it?), so I suppose that could make it more prone to knocking at low revs.

I should mention a few things:

1) The engine has a high CR (12:1) and tuscan cams
2) The fuel has been sitting in the tank for a few months now
3) Lambda 1 seems to be buggered, as it was sitting on 0.1V

Lastly, if it isnt pinking, what the hell else could it be?

Many thanks in advance, Rob.

[Boosted LS1]

FWIW pinking is usually a light sort of a noise which you would get under load around peak torque or at higher rpm's say when hammering a cavalier down the motorway. I've experienced knock at low revs, high gear at a crawling speed making a turn. It sounded like a bloke bashing my engine block with a hammer!

Have you disturbed anything mechanical as that's what I'd check for first?

[brogenville]

Well, as its the first time the engine has run since fitting it in the car, you could say that I've disturbed a lot of things. Still, externally, the crank pulley and the alti belt both look free from anyting that might touch them, so unless its pre-det, I would think that it could only be something else unpleasant happening inside the engine.

[Storer]

It's not the exhaust manifold touching on the chassis on a lumpy tick-over?

[brogenville]

Storer said:

It's not the exhaust manifold touching on the chassis on a lumpy tick-over?

Afraid not- manifolds have been wrapped, so if it was then the sound would be a dull thud rather than a sharp ting.

[GreenV8S]

Not sure how much you've changed recently, but if you've changed the ECU or any of the hardware associated with crank position sensing, is it possible you're getting ignition timing jitters or interference on the crank trigger signal? This could lead to an occasional early spark giving the audible knock.

[brogenville]

GreenV8S said:

Not sure how much you've changed recently, but if you've changed the ECU or any of the hardware associated with crank position sensing, is it possible you're getting ignition timing jitters or interference on the crank trigger signal? This could lead to an occasional early spark giving the audible knock.

Well Im not getting an crank position error code, but I'll check to make sure there I havnt done anything dumb like twisting the crank position wire around and big wires.

Apparently what Im hearing cant be pinking as such, as on idle there isnt enough air entering the cylinders to generate the pressure required to pre-det.