Help!! Engine Miss

[Ben Kallies]

Monte,

I've got an Autometer shift light, triggered by an MSD RPM activation switch. I disconnected this as well in the course of testing.

-Ben

[Ben Kallies]

OK, so the leakdown test is done. I checked each cylinder twice with the same results each time. Results are as follows:

cyl 1 12%
cyl 8 10%
cyl 7 11%
cyl 3 7%
cyl 6 5%
cyl 5 12%
cyl 4 11%
cyl 2 8%

It's my impression that these results are good. Thoughts, comments? Is a compression test still necessary, or do these results verify the health of the engine?

Thanks,

-Ben

[Tim Lisson]

Not sure what you are running for rings, but if that was my numbers the engine would be out of the car. Either way, ring seal would not cause the problem you are describing.

Did you warm the engine up a bit before beginning your test?

Tim

[Mike Taylor 3601]

Thats not great but not terrible,10% or less is good naturally the less the better,2-3%is really good. I would remove rockers and intake manifold,headers and hook air straight from air hose full pressure to plug holes and cover port with hand to see if feel pressure leak through valves,if air is coming through intake valve at all engine will not run right compression coming back in intake runner messes with signal to carb.

I have seen engine leakdown good compression test show good,but find valves leaking with air, seal valves and fix problem,may not be problem with your's but I would test it.

If intake valves are leaking enough it could act like your description,compression leaking in runner messes signal to carb.will make miss or can make unable to tune you can change jets and not make any difference I seen one w/valves leaking slightly would die like you shut key off @ 6000 fixed valves back to 8800


Mike Taylor 3601

[Tim Lisson]

You mentioned in one of the posts recently it does rev up freely without load? You need to take this to a drag strip and get after it.

Also, i would verify your alternator is working properly along with a seperate ground wire from the alternator to the head. I know what your thinking, it's bolted to the block...

[KRatcliff]

Originally Posted by Tim Lisson

You mentioned in one of the posts recently it does rev up freely without load? You need to take this to a drag strip and get after it.

Also, i would verify your alternator is working properly along with a seperate ground wire from the alternator to the head. I know what your thinking, it's bolted to the block...

It is funny you mention that. I bought 100' of the braided ground strap material from Ebay. Do you know how far 100' will go?

Lets just say that if I ever crash my car, I won't die from the impact. It will be from strangulation.

[Ben Kallies]

Tim,

Leakdown test was performed cold. Engine hasn't been run in 2 weeks.

-Ben

[Tim Lisson]

Ben,

First of all, I'm no expert so take this for what it's worth....

1) After dyno session, did you back the rockers off when it sat until you got it in the car?

2) When I do a leak down, I typically run the car up to 140-150 then attempt to zip through the test with warm cylinders. The cylinders that are over 5% I would smoke test, go by a cheap cigar and have it over the carb/intake opening and exhaust port/ header tube when performing this scientific test... don't laugh, it works.

Other than everything else mentioned, get it to a track or bring it up north. My trans builder has a chassis dyno and has had many BBC on it. Sounds like a fun mystery!

Tim

[MikeMoller]

Originally Posted by Ben Kallies

OK, so the leakdown test is done. I checked each cylinder twice with the same results each time. Results are as follows:

cyl 1 12%
cyl 8 10%
cyl 7 11%
cyl 3 7%
cyl 6 5%
cyl 5 12%
cyl 4 11%
cyl 2 8%

It's my impression that these results are good. Thoughts, comments? Is a compression test still necessary, or do these results verify the health of the engine?

Thanks,

-Ben

Run a compression test anyway. If you have a flatttened cam lobe-particularly intake- the compression may show low on that/those cylinders. Happened to me on a brand new motor.

Mike Moller

[Gary Wiegand]

Hi Ben,

This is my first reply on this site, so hopefully I get it done correctly.
Before I describe a similar situation which I had, trying to chase down a "miss" in the engine, and what was causing it, I have one question; do you have a spacer plate below your carburetor?