Does anyone have a write up or know where a write up may be on how to preform a leak down test on an 2005 Evolution 8? have a Mac leak down tester and an air compressor, just need to know if there is a write up somewhere.

 

Bump for Drew. Let's give the man some help if you have a leak-down test how-to!

 

wouldnt it be the same as any other car? I have not done one to the evo so I cant say. But normally dont you bump the pressure up to 100psi and then after a set time (one min) see what the pressure drop is? Thats what your leak down tester has the two gauges for right? Oh..and some way to keep the cylinder from spinning backwards such as a breaker bar on the crank.

Or am I totally off?

 

Isn't that a compression check?

 

no. a compression check you crank the motor. a leak down you are measuring the pressure lost over a period of time. 100psi, after one min you have 90psi left...your leak down rate is 10%

 

here you go

http://www.type2.com/library/engineg/leaktst.htm

And an explaination;

a compression test checks for how well each cylinder is sealing when the engine is rotated. All of the cylinders should be close to each other in the amount of compression that they generate during the test....this shows that all of the cyllinders are sealing properly. A lower number in one or more of the cylinders means that something in that cylinder is not sealing properly....allowing air to escape.

Usually, after a compression test that has lower numbers, you first squirt a bit of oil into the cylinder to wet the rings and perform the test again. If the compression numbers go up, it's due to the rings not sealing properly. The oil added helps them to seal better causing the numbers to go up. If there is no change with the oil then something else is causing the leak. This is where the leakdown test comes into play...identification of the leak.
Leakdown is putting the cylinder at TDC (where all valves should be closed) and pressurizing the cylinder. You then read how much of the pressurized air is leaking out of the cylinder. If the leak is excessive, usually you can listen to different parts of the car for the sound of escaping air to identify the source of the leak. If you hear it from the exhaust, one of the exhaust valves is the cuplrit. If you hear it from the induction system, one of the intake valves is the problem. If you see bubbles in the coolant or hear it bubbling in the cooling system you got a headgasket problem, etc...

 

Ah thanks. I should know better. I stood and watched the guys at Speed Element do a leak-down on my '05.

 

Ok, thanks for the link. what i am looking for is basically how much psi i should pressurize the cylinder too. those instructions say that you should have an air compressor that can go to 90psi, so is that saying pressurize the cylinder to 90 psi? I have done various leak down tests before but never on an Evo or anything turbo or supercharged, and that is why i was wondering if there was a different proceedure or if it needed to be pressurize to a different amount. would HATE to be wrong

 

also i have already done a compression test to my Evo, that is a piece of cake. I got 180psi on 3 of the cylinders and 186psi on the last one.

 

The pressure is not really a big deal. 90 psi is okay. Your compression check goes to 180 so dont worry about overpressurizing the cylinder. the reason I suggest 100 is that it is easier to figure out a percentage of loss. Usually there is an acceptable amount (just like the compression check--below 150 or differences between cylinders as an example) I would say I think over 15% is a major problem with a leak down. Something is going to escape somewhere, most likely the rings. You dont want a major leak in the head gasket (bubbles in coolant) or air in the exhaust/intake.

 

mitsubishi allows results of 18-20% for a leak down test.