Compression and leak down test results

Actually I think number 2 being low is normal but I forget why.
Sorry
Maybe someone can chime in about 1 cylinder being low??

 

70% leak is no where near normal. These cars driven little with poor mixture control certainly can foul. I have seen caked intake valves often. GM topend , seafoam, and techtron used in higher concentration on a nice long drive or even a trackday is not going to hurt anything if damage has already been done. But if you don't get a significant improvement its time for doing the heads, inspecting the headers, and ensuring proper mixture control.

 

You missinderstood normal.
I meant there is a failure which oftain occurs but I can not remember which cylinder. Maybe you remember Fbb

 

7

 

I new you would.
Thanks

 

It is either 2 or 7 that fail. Good advice to spank it hard for a few hundred miles and if it does not improve then it's time for valve guides.

 

My 348 with 11,400 miles had 190 on all 8 and 5% leak down with the exception of #5 which was at 8%. 240 seems quite high, maybe its a 355 and that's how they are?

 

Your numbers make little sense. 240 PSI is extremely high especially at a 15% leak rate. Something is wrong with these values.

If your number 2 is 70% leak, you have a valve with a piece missing.

 

well calcs show range of 182-217 psi.....11% harbor freight gauge error?

 

If your gauge is accurate, and they never are absolutely accurate, 240 psi means you have a lot carbon build up inside the chamber. If a valve is missing a piece, and it normally is the exhaust valve that is missing the piece, your leak down would be 100%.

 

I would definitely run the top engine cleaner through it first. I have used it on vehicles that were heavily carbon caked and it works really well. Cars that are run on short drives or just started and shut off can build up carbon. It needs to be driven to full temp and spirited, that helps keep things clean. And using good quality fuels help too.

 

I will go on a limb and say the process was done wrong or equipment was not used correctly. There is a whole slew of things that can be done improperly that give wacky numbers. I would suggest a second opinion as it were.

Definitely you run the top end cleaner through before pulling the engine, try seafoam SS14 and the one you pour into the fuel I forget exactly. You can find it. Used it in cars before as well as most people i know. Be advised it pisses neighbors off.

 

Run the BG pressure pot through the motor then take it on a long hard ride with their addatives

 

I use this system by BG

 

Just use the same system in this configuration. Carbon buildup is no new issue and something thats become part of regular maintenance with direct injection

 

I would think overall high cranking compression -could- mean advanced intake cams

 

Motors with more than 10% leakdown are at the point where a rebuild is desirable.
11:1 Motors rarely have more than 170-180 PSI on a compression gauge.

Then you are looking at a weak 7 cylinder engine.