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2G No compression on 1&4 after rebuild

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Loueg702

Probationary Member
7
0
Jul 11, 2021
Las Vegas, Nevada
Ok so after 2 years of learning what to do and what not to do on rebuilding a 2g to stock specs I’m at a stupid problem I’m hoping someone can help me with.

Long story short, it’s a standard size stock rebuild 1996 Gst. Everything went together fine. Cranks good. Doesn’t leak anything I put in it. Full power. Everything works as should…won’t start. Here’s my issue..compression reads 0 on cylinders 1 & 4 only. 2 & 3 are 150+

The things I’ve checked

Rings : took the head back off rechecked rings all are good. Did the ATF fluid in the cylinders and did a compression test still at 0.

Leak down : did a leak down and it’s shows complete leakage in cylinder 1 and 4.

Smoke : blew smoke into the intake and anywhere else trying to get it to show and nothing.

Rubber glove on intake sucks in and out when cranking

My question is..timing? Bad head gasket? Has to be something stupid..head was decked and redone (supposedly) at the machine shop. Block was dipped and cleaned up at the same place. Odd to me that I have complete sealage in the center of the engine and both sides are leaking. Anyone experienced this?
 
Leak down : did a leak down and it’s shows complete leakage in cylinder 1 and 4.
So you ran a leak down test and you have 100% leakage in #1 and 4. Just distinguish from where the air is escaping by hearing. That's what a leak down test is.
 
So you ran a leak down test and you have 100% leakage in #1 and 4. Just distinguish from where the air is escaping by hearing. That's what a leak down test is.

Smh. If I was that dumb I wouldn’t know how to do a leak down test. I can’t hear or see anything to be honest. I tried soap and water, listening, even though it’s kinda hard to get your ear anywhere but hovering over the engine bay or underneath. Trying again in the morning.

Did you bleed the lifters? Maybe one was stuck and now that you’ve cranked it possible bent valve(s)

They were new. Soaked em, all moved when I installed it. Pulling the valve cover and redoing the timing in the morning to inspect and hopefully I’m just off a tooth. I could see that with one cylinder but 2 plus them being 1&4 with 2&3 being fine is unlikely. But possible.

When I had 0 compression on the #1 cylinder on my new motor it was 2 bent intake valves from improper block/head assembly:ohdamn:

Could see that if it was 1 cylinder but I got the valves redone and didn’t see anything when I had the head off. Just strange it’s 1&4 and those are down while 2 and 3 are up, makes me think it’s timing.
 
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Smh. If I was that dumb I wouldn’t know how to do a leak down test. I can’t hear or see anything to be honest. I tried soap and water , listening , even though it’s kinda hard to get your ear anywhere but hovering over the engine bay or underneath. Trying again in the morning.
If you seriously have 100% leakage on #1 and #4 and if you didn't realize anything while running the leak down test, then you didn't do it properly. You don't need soapy water, what you do is just focus to listen/feel the air. Maybe it's hard to hear hissing sound but obviously you would feel a lot of air coming out from intake port or exhaust port or crank case while you are charging the air into the cylinders. Remove intake manifold and exhaust manifold would make it much easier.

I don't understand somethings, so you just rebuilt the engine and already drove the car once but it didn't start again? Or haven't started the engine yet?
Most of cases, valves are badly bent or widely open for some reason when you see 100% leakage. In this case you can visually see it the bent valves by just removing valve cover. Should check it before running another test.
 
If you seriously have 100% leakage on #1 and #4 and if you didn't realize anything while running the leak down test, then you didn't do it properly. You don't need soapy water, what you do is just focus to listen/feel the air. Maybe it's hard to hear hissing sound but obviously you would feel a lot of air coming out from intake port or exhaust port or crank case while you are charging the air into the cylinders. Remove intake manifold and exhaust manifold would make it much easier.

I don't understand somethings, so you just rebuilt the engine and already drove the car once but it didn't start again? Or haven't started the engine yet?
Most of cases, valves are badly bent or widely open for some reason when you see 100% leakage. In this case you can visually see it the bent valves by just removing valve cover. Should check it before running another test.
So I did another leak down and yes I know how to do it right.

What you’re saying is based off the fact there is a huge leak that’s obvious . I know major leakage should be heard but it’s not always that simple. That being said I did another one this morning and felt air coming from the intake. I’m going to take your advice and remove the intake to get a better idea but upon inspection I didn’t see any bent or broken valves.

I think they possibly just aren’t seated right. Will keep the thread posted.

Oh and I never said I drove the car, I said it won’t start. It hasn’t even fired up. I just cranked it and never got it to start which led me to do further investigation.
 
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Take the head off and do a combustion chamber water test. You turn the head upside down on a bench, pour water into the combustion chambers and see if they hold water; I bet two of them don't. If they do hold, shoot some compressed air into each port and make sure there are no bubbles in the chambers.
 
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