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Discussion Starter #1
Hello people. My car is 91 MR2 Turbo with 98,000 original miles on it. I normally don't boost my car a lot maybe once/twice a month. To make long story short, last week my car suddenly had lost its power during driving on the Freeway. Whenever I tried to press on the gas the engine would shake a lot without any boost. There was also some ticking noise from the engine/valve cover. I think my engine is gone, so today I did dry and wet compression tests.

Dry compression test result:
1=170, 2=170, 3=170, and 4=60 <-- !!! :furious:

I was surprised that 1, 2, and 3 were just perfect but why the forth one seemed to be really too low than others. So I began to put engine oil (about 1/5 QT) into 4th cylinder and do the wet method.

Wet compression test result:
(Only) 4th cylinder=60 <--??? :confused:

I did the same 5 crankings and I got the same result. I thought that when we put engine oil in, the compression would rise up because the oil helps to seal the piston ring gaps.

Now my questions are: Why did I get the same result? Is my engine/piston ring really damaged? What are the possibility causes? And what should I do?!? From what I can think of is the valves on 4th cylinder are stuck open, is this possible?

Thanks,
JDMR2TT
 

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JDMR2TT said:
Now my questions are: Why did I get the same result? Is my engine/piston ring really damaged?

What are the possibility causes?

And what should I do?!?

From what I can think of is the valves on 4th cylinder are stuck open, is this possible?

Thanks,
JDMR2TT
Very probably

Detonation

Rebuild, or get a new short block

Possible, but not really very likely. If a valve was stuck open, you woujldn't even get 60 psi.

bill
 

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Discussion Starter #3
^^
Don't I need to rebuild the head too?
why I still get same 60psi on wet and dry compression test?

JDMR2TT
 

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same result coz theres either a big big big hole in the piston, but for 60psi i doubt it.

More likely damage to valves? your going to have to pull the head and take a look.

Graeme
 

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JDMR2TT said:
Hello ..... There was also some ticking noise from the engine/valve cover. I think....JDMR2TT
remove the valve cover and inspect the shims of the #4 cylinder....

Lawrence
 

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Discussion Starter #6
Ok guys thanks for reply. I'll take the head out before the next weekend and I'll take some pictures for you guys to see. My car has only 98,000 miles and I've been taking a good care of this car more than my girlfriend!!! I hope I don't have to rebuild the engine so soon although there isn't even 10% chance... :cry:

JDMR2TT
 
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JDMR2T, there maybe some of valves are opened or not fully closed. How do I know? I faced similar problem on last week so I took my car the the repair shop. After diagnostics the mechanic found out that the valves were not fully closed and I ended up fixing it instead of rebuilding the engine.

Look at BGG under "Compression Check" section. It said:
-If adding oil helps the compression, chances are that the piston rings and/or cylinder bore are worn or damaged.
-If pressure stays low, a valve may be sticking or seating is improper, or there may be leakage past the gasket.

You still have a chance more than 10% but don't expect much.
 

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Discussion Starter #13
^^Thanks for your suggestion Tee :) . I'll take the valve cover and maybe the whole head off to see how my pistons doing in there by this weekend.
JDMR2TT
 

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could be burned valves or a blown headgasket I would bet its one of the two. How did the spark plug look in Cylinder 4?
 

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put pressure into that cylinder and see where the air comes out.
Bad rings/piston - PCV
Bad headgasket - Usually coolant bubbles (also possibly PCV)
Bad valve(s) - Intake/exhaust
 

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MR2000GTE said:
put pressure into that cylinder and see where the air comes out.
Bad rings/piston - PCV
Bad headgasket - Usually coolant bubbles (also possibly PCV)
Bad valve(s) - Intake/exhaust
make sure the cylinder youre testing is at tdc
 

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Discussion Starter #17
Thank you very much for all of your responses. Now I know what the problem is.

The winning guessing award goes to "paaik" :cheer2: The problem I have is that one of the valve got burn!!! This is the first time I saw burned valve....how could this happen? Too much carbon build up and catch on fire?!?

JDMR2TT
 

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JDMR2TT said:
The problem I have is that one of the valve got burn!!! This is the first time I saw burned valve....how could this happen?

JDMR2TT
The most common reasons are running lean or too much advance.

bill
 
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