Lone Star XJ
NAXJA Forum User
- Location
- The Woodlands, TX
I am trying to run down the cause of Cylinder 1 misfire. A compression test yielded 145/150psi on #1 and my other five are 160~170psi. I did not have a compression leak down tester, but I connected my air compressor to cylinder one and used the regulator to put 80psi of air in it. Cylinder #1 was at TDC and I could hear a little air through the oil fill hole in the valve cover and through the throttle body. There were no bubbles in the coolant and no air coming out the exhaust.
I turned the engine over and tried the test when the intake and exhaust valves were open. At all positions I could hear a little air coming out the valve cover and throttle body. The air coming out the exhaust was minimal.
I then tried it on cylinder two and I could also hear a little air coming out the valve cover but nothing out the throttle body. Trying the test on the intake and exhaust stroke yielded a big rush of air out the throttle body or exhaust.
Will you always hear a little air out the valve cover when doing a leak down test? I would think so since no cylinder will seal 100%. Since I can hear air out the throttle body, this would point to a problem with the intake valve. I have run Mopar combustion chamber cleaner and some MMO with no change. I can hear some kind of tick when the engine is idling. It doesn't sound like a valve but maybe a lifter. I don't know as I have no experience with hydraulic lifters. Last thing, the misfire is worse when starting the engine for the first time in the mornings and this is when it will throw the code. When the engine gets good and hot it just about goes away and the computer does not throw a code. You can also pull the spark plug wire or injector wire and the engine will bog down as it should. I will not do this when it is colder.
I turned the engine over and tried the test when the intake and exhaust valves were open. At all positions I could hear a little air coming out the valve cover and throttle body. The air coming out the exhaust was minimal.
I then tried it on cylinder two and I could also hear a little air coming out the valve cover but nothing out the throttle body. Trying the test on the intake and exhaust stroke yielded a big rush of air out the throttle body or exhaust.
Will you always hear a little air out the valve cover when doing a leak down test? I would think so since no cylinder will seal 100%. Since I can hear air out the throttle body, this would point to a problem with the intake valve. I have run Mopar combustion chamber cleaner and some MMO with no change. I can hear some kind of tick when the engine is idling. It doesn't sound like a valve but maybe a lifter. I don't know as I have no experience with hydraulic lifters. Last thing, the misfire is worse when starting the engine for the first time in the mornings and this is when it will throw the code. When the engine gets good and hot it just about goes away and the computer does not throw a code. You can also pull the spark plug wire or injector wire and the engine will bog down as it should. I will not do this when it is colder.
