VR6 internal popping?

[MarkGolf 0]

Hi,

 

My newly built VR6 sometimes sounds a 'POP' noise.. It's hard to tell exactly where it's coming from but it is from inside the engine, nothing surrounding. It's not continuous or at regular intervals, just now and then.. A friends seems to think it's possibly an air leak or a slight misfire but to me there doesn't appear to be a misfire..

 

Any ideas?

 

ThANKS

[Critical_Mass 10]

Does it do it underload, just revving the engine or is it on overrun. Any idea where abouts its coming from. What do you mean inside the engine. Are you sure its not popping in the exhaust manifold?

 

Does it drive like its got a misfire?

[MarkGolf 0]

It does it just sitting on the spot, the car will rev perfectly..

 

It is 100% in the engine, after doing 1 of many test runs, the inlet manifold was only held on by 2 bolts and it was pretty dark, upon each 'pop' a flash of light could be seen through the join of the upper and lower manifolds..

 

The idle is very lump too!

 

http://www.youtube.com/watch?v=9g_2EBlAusU

 

Since that video I've fitted a brand new coilpack and removed my denso plugs and fitted the rated NGK items.. It has NO misfire now, just a lumpy idle, overfueling and the popping!

 

I'm stumped, it doesn't even sound like a VR6 when it's rev'd :s

 

I did strip the engine down on Saturday, with the timing tool in place on the cams, the timing marks on the crank pulley lined up perfectly so I assume the timing is fine.. I have brand new schimmel leads, new plugs, new coilpack so the ignition side of things is fine..

 

The only 'old' items are, MAF, Lambda, TPS and CPS..

[andy 0]

Its a while ago I had mine apart but I seem to remember that you need to check allignment on more than the cams and the crank pulley. I have some recollection that you can have the cams and crank alligned correctly but not the intermediate pulley. This would put your valve timing out, which I think your symptoms have a whiff of. Have you checked the intermediate pulley?

[Kevin Bacon 5]

Indeed, the intermediate shaft needs to be pointing North and has been the topic of much debate on here for a while now :D

 

It can also point south, but in respect of checking it for fault finding, the marker is only visible (engine in situ) when pointing North, so that's where I'd set it personally.

 

Anywhere in between N and S is a big no no. It does indeed shift the cam timing slightly.

 

And regarding the intake, ideally you should have all the bolts in and torqued down to get a gas tight seal. You'll be surprised how much air can leak through a manifold join that isn't tightly sealed. The flash of light you saw through the manifold gap is probably pre-ignition due to the mixture being too weak.