I'm in the middle of a leakdown test trying to troubleshoot a problem that has been keeping me off of the road for many months after a cam and heads install. I keep running really rich on the passengers side and have a tendency to foul #6 and #8 plugs after only thirty minutes of motor operation.

After removing my roller rockers from the intake and exhaust valves from #8 (plug that usually looks the worst), I hooked up my leakdown tester to the cyl. While the air compressor tank pressure read 101 psi , the left gage (regulator) on the tester read 90psi, and the right gage read 70psi. I could hear air escaping but couldn't pinpoint exactly where it was comming from. It sounded like it may have been comming from inside of the intake or maybe the head??? I tried this test on #1 which I'm almost 100% sure is good and got the same reading? When I subtract the reading of the left gage from the right gage I get 20, which is not on the leakdown chart that I have. The most that I have on the chart is 15 psi difference. So to clear things up, does that mean that I'm getting less leakage or too much leakage. And how can I find out where I'm hearing this air come from? Thanks for all of your help!

 

There is usually a percentage on one of the guages that tells you what percent leakdown you have. If you hear air, thats not good. Probably have a leaking valve or something. 90 down to 70 isnt very good...

 

Yea, I didn't think that 90 down to 70 was very good but I thought that maybe I was doing something wrong because I got the same thing on both # 1 and # 8 which was the suspected bad cyl. I could hear air escaping but couldnt tell where. thanks for your input.

 

How do you tell where exactly the air is comimg from if you hear it inside of the motor? Should I take off my headers and check the exhaust ports on the heads. I took some of the vaccume ports off of the intake manifold and didn't feel any air comming from there.

The Exhaust fumes really smell like fuel so wouldn't that point me in the direction valve damage rather than piston or ring damage?

 

If you put a couple of squrts of oil in the cyl and a with a COMPRESSION test it raises the number on the guage,it is rings,If it doesn't raise it it is valves.Check all cyls dry first then the low ones squirt some engine oil in them and retest.Let the engine bump the guage at least 4 times,more won't hurt,and turn it with the starter with the coil wire disconected from the opti and the coil grounded.
A leak down test with over 15% is not accurate,so use a compression test to determin what it is.

 

Didn't know that I could do that with a leakdown test. Thanks for the info. I've been working so much lately that I have not had the time to try again. I'm hoping that because I was rushing to get it done that maybe I wasn't doing the test right.

 

You would have to do a compresion test to isolate the two.

 

That's true, the reason that I'm concentrating on a leakdown test is because I am getting a small amount of greyish smoke comming out of the oil fill cap after running her for a while. That tells me that something is wrong with the valve or valve seat on #8 or #6 (which I recently replaced for bigger HP gains), or at least that is what I'm hoping for on a worst case senario. I installed those comp R lifters and they seem really hard to get adjusted just right. I just don't see how I could have been dead on with adjusting all of the other rockers and messed up several times in a row just on #6 and #8. I'm not denying that the comp r's arn't good lifters but I guess that it is possible that I may have a bad lifter that has only 30 miles on it. I guess I'll find out with another more carefull leakdown test hopefully tomorrow, unless I get called in to work. For some reason I have a hunch that something smaller is causing this though...I hope