1G stock compression?

kennybbm · Dec 12, 2020

what is the original compression in psi of the eclipse?
Mitsubishi Eclipse GS 1992 (engine is original,no turbo)
i got: 120 psi, 0 psi, 120 psi, 120 psi

how good are 120 psi in terms of engine health, and what could be wrong?
at 200 km/h i felt a power loss. at lower speeds it felt like 50 percent less than usual. the engine rumbles a little bit when pressing the throttle. i dont hear any scraping noises or whatever it just sounds like it runs only on 3 cylinders(obvius with zero compression on one cylinder)

what happens? piston rings damaged? head gasket(there is no smoke)?

george bromwell · Dec 12, 2020

kennybbm said:
what is the original compression in psi of the eclipse?
Mitsubishi Eclipse GS 1992 (engine is original,no turbo)
i got: 120 psi, 0 psi, 120 psi, 120 psi

how good are 120 psi in terms of engine health, and what could be wrong?
at 200 km/h i felt a power loss. at lower speeds it felt like 50 percent less than usual. the engine rumbles a little bit when pressing the throttle. i dont hear any scraping noises or whatever it just sounds like it runs only on 3 cylinders(obvius with zero compression on one cylinder)

what happens? piston rings damaged? head gasket(there is no smoke)?

i think you'll have to rebuild the engine, but obviously 0 psi is bad, but the service limit for low cylinder psi is 145 psi for 2.0 non turbo. so across the board you're below spec. there are several things that could be happening, but for a proper inspection and rebuild its probably time to pull the engine. sorry to hear about your troubles. i have a spare turbo 4g that needs a rebuild if you're looking to go turbo

kennybbm · Dec 12, 2020

george bromwell said:
i think you'll have to rebuild the engine, but obviously 0 psi is bad, but the service limit for low cylinder psi is 145 psi for 2.0 non turbo. so across the board you're below spec. there are several things that could be happening, but for a proper inspection and rebuild its probably time to pull the engine. sorry to hear about your troubles. i have a spare turbo 4g that needs a rebuild if you're looking to go turbo

i dont plan to put a turbo in because in my country it would cost huge amounts of money to do that legally.... a rebuild is hard to pull off because i never did it before. but i guess thats the only option. i may be able to seperate the engine,then i would have to give the block for machining and order new parts.
my first guess right now for parts:
headgasket
pistons
piston rings
(valves)

machining:
block
valve seats
valves

cylinder head should be checked too. but i guess there is not the main problem. thank you for the answer!

Mech Addict · Dec 12, 2020

I would thing that you would have some compression even with a broken ring, unless it took out the second ring as well. I’ve not really heard of a broken valve. Did you try the oil-squirt trick during the test? Likely doesn’t matter. If you’re doing the work yourself, you could start by removing the head, and getting a look inside. With all the cylinders that low, probably doesn’t matter. Few questions though:
How many miles?
Are you confident you did the compression test correctly?
Your description seems like one cylinder is dead, yes, but an improper test and broken plug wire are one possible explanation. Just throwing it out there...

pauleyman · Dec 12, 2020

You guys are talking about rebuild without knowing the cause of these numbers. Check mechanical timing. My bet is timing is off and you have bent valves. The key is it was fine them all of a sudden it wasn't??? Thats not rings folks. This could be a head rebuild. Op you need to find out what went wrong.

WisconsinMonSTAR · Dec 12, 2020

Do a leak down test to see where the loss of compression is coming from. Lots of possibilities on what it could be.

In my case years back, I had an injector fail, causing a lean condition in one cylinder which burned the edges of my exhaust valves. I had similar symptoms: sudden loss of power, engine running rough.

Head gasket or piston rings would more likely cause low compression but not zero. I suspect damage to the valves.

Sjd6795 · Dec 12, 2020

I just recently did a head rebuild on my 4g63t, I figured my head gasket was trashed and the reason I had no compression in one of my cylinders. Turns out when I had everything apart I had completely melted one of my exhaust valves, due to lean issues. Now being non turbo I doubt you have a melted valve, but it could be other damages like everyone has stated. Don't just go buying new random parts because you suspect them to be bad, take the engine apart inspect it then go from there.

DSMPT · Dec 12, 2020

I would suspect some valves stuck open for some reason, first I would check the valve timing like @pauleyman Paul said above. Maybe the intake suck some foreign object and stuck on a valve, too. In case if the zero compression issue is caused by rings, OP should have seen a lot of blow-by gas or/and smoke.

kennybbm · Dec 13, 2020

Mech Addict said:
I would thing that you would have some compression even with a broken ring, unless it took out the second ring as well. I’ve not really heard of a broken valve. Did you try the oil-squirt trick during the test? Likely doesn’t matter. If you’re doing the work yourself, you could start by removing the head, and getting a look inside. With all the cylinders that low, probably doesn’t matter. Few questions though:
How many miles?
Are you confident you did the compression test correctly?
Your description seems like one cylinder is dead, yes, but an improper test and broken plug wire are one possible explanation. Just throwing it out there...

I got spark on all the cylinders except the one that has 0 compression. did the compression test three times on the suspect, i will do it again. but what can fail when doing the compression test? screw the adapter in and the hose too. plug in to the gauge and run it for at least 4 strokes. i dont do the oil trick(i guess you mean to squirt a little bit of oil into the cylinder to have a better seal between the rings and block?)

*edit*

I did now the oil trick and several tests again. still 0 psi and 120 on the others. next weekend i try new spark cables and distributor. but there will be still 0 psi. then i take a look at the valves. btw, the thread on the sparkplug hole at the head looks ok. i also dont hear any air escaping there...so i guess i didnt fail at testing.

pauleyman · Dec 13, 2020

If you have zero comp something is broken. Leakdown will tell you what.

pauleyman · Dec 13, 2020

kennybbm said:
I got spark on all the cylinders except the one that has 0 compression. did the compression test three times on the suspect, i will do it again. but what can fail when doing the compression test? screw the adapter in and the hose too. plug in to the gauge and run it for at least 4 strokes. i dont do the oil trick(i guess you mean to squirt a little bit of oil into the cylinder to have a better seal between the rings and block?)

*edit*

I did now the oil trick and several tests again. still 0 psi and 120 on the others. next weekend i try new spark cables and distributor. but there will be still 0 psi. then i take a look at the valves. btw, the thread on the sparkplug hole at the head looks ok. i also dont hear any air escaping there...so i guess i didnt fail at testing.

Do not bother buying new cables. You're pissing in the wind. You need to find the cause of the zero comp. What happened leading up to this? Im guessing you skipped time and you have bent valves. Find the root cause first. We've given you all the information you need. No amount of external parts will solve this. The problem is internal and you have to find out the cause(s) and fix them. Short of pulling the head off leakdown is likely your most definitive test

Mech Addict · Dec 13, 2020

Yes, I wasn’t suggesting this was likely an ignition issue; just that there could be a host of potential reasons for the car to run down a cylinder, and show 0 compression. I’ve had my share of incorrect testing, and jumping to wrong diagnosis. Pauleyman’s suggestion really only requires removing the upper cover, so pretty easy. Leakdown also not too difficult. More details on the early symptoms will help us all with troubleshooting.

motomattx · Dec 13, 2020

Melted exhaust valve would be my educated guess.

kennybbm · Dec 26, 2020

spark plug and cables are good. tested them again in the daylight. will do a leak down test in the next days when i have the set. checked the ecu, the check engine light was on because of the oxygen sensor. replaced it and its gone now. thanks for all the help!

92AWDHX40 · Dec 26, 2020

Well sounds like your getting there.

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