Valley vac leak symptoms?

[John Milmont]

I'm still troubleshooting my engine and as Jim Cowden suggested, I'm thinking I could have a valley leak.

The thing is, my engine is speed density, so i have no MAF sensor metering the air. I'm not sure how a vac leak will effect the engine because of this.

Right now, cylinders 1 and 7 are 300 and 400 degrees colder than the rest. I have noticed oil on the spark plugs of those cylinders so I'm thinking its got to be bringing the oil in from somewhere like the valley. I have done a compression test and leak down test on all the cylinders and everything is within spec, so I don't think the oil is coming up through the rings.

I guess I will try to spray some starter fluid in the valve cover to see if that changes the idle; but does my problem sound consistent with a valley leak?

Thanks

 

[Cliff Beer]

John, that does indeed sound like a very real possibility. Do you get any condensation out the exhaust? My (limited) experience has been that if the inlet manifold gasket has let go then there can be a fair bit of white water vapor out the exhaust pipe due to coolant getting into the chamber too. Incidentally, that'll steam clean your compression chambers real good.

After having a few inlet manifold gaskets go bad I developed a little method of my own to get the manifold to seal: loosen the head bolts somewhat and tighten everything up to spec concurrently. I think this allows the heads to square up a bit on the manifold as it's all being tightened down. Obviously, use good quality gaskets. I use the cork gaskets at the end of the valley to seal that up, even if they do look a little fat going in (the cork compresses and seats fine).

It does sound like you have oil fouling 1 and 7 causing mis-firing.

 

[Jac Mac]

Have you taken the rocker covers off & checked that all the valve stem seals [ inlet in particular] are still fitted correctly.

Another thought that might be of help to you...couple of weeks ago I had to refit an inlet manifold to an NZV8 touring car, due to the stupid lengths the dummies at MSNZ have gone to or allowed to happen under the guise of parity with other makes it has become somewhat problematic & critical to line up the manifold ports with those of the cyl head & the choice of inlet manifold does not allow for 'line of sight'. Soo, what to do, solution was a cheap autostore miniature B&W TV camera with a flexible camera wand, one of these items passed down your intake runners might help pinpoint the cause /area of concern in your case, I know in ours we ended up removing the manifold and refitting with some thicker custom gaskets to get the correct port lineup etc [ along with a lot less sealant...]

 

[John Milmont]

I did have the rocker covers off, I actually dressed these heads. The valve seals look good so I don't think thats an issue.

Jac Mac, I think the manifold gasket could be the issue. I remember some funky fitting when i was putting it together. I'll have to take a look at it this weekend.

 

[John Milmont]

Well, pulled off the intake and everything looks ok. While I had it off, I decided to test the injectors just to erase any doubt they could be a problem. I had already swapped them around without any change, so I was pretty sure they were not the issue.

Attached some pictures of my injector test. I found that the injectors are more accurate than the graduations on my cheap graduated cylinders...

I'm thinking that, through the process of elimination, I have some bad lifters and that's whats causing the problem.