# Compression Test



## zakgord (Jun 11, 2007)

*Results I posted in another forum after my compression test...*



> Okay, test was successful. I forgot to block the throttle open. Just cranked her over with out stepping on the pedal...would that throw the numbers off?
> 
> Here are my results (Note these were done with roughly 5 strokes of the motor, with the compression rising less each stroke ex: 120...140...155..165...175psi approx):
> 
> ...



*A few questions...*

1. What does that unusually high compression suggest? Maybe I added too much oil....who knows?

2. Do my numbers on the first dry run seem ok? Was the wet test needed?

3. My reason for conducting this test is because of a rough idle/ 0302 misfire on cyl 2 code (plus knock sensor of course). I've checked a few things so far as posted in prior posts (plugs, wires, dist/cap, egr valve works properly, no vacuum leaks, I sprayed around intake gasket...didnt cause the idle to smooth out., listened to the injectors and all were clicking,....what else could I do to figure out this misfire?

4. I've been researching quite a bit the last few months and checking these things...still no answers getting fustrated...but i might just drive the engine til it dies and put a new engine in....it runs fine when not idling and getting approx 27 - 29 mpg. Sound like a reasonable solution?

5. Could the leaky exhaust manifold gasket cause a rough idle/misfire on cyl 2?


Thanks for anyone who reads through this posts and anyone who may offer some help.


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## zakgord (Jun 11, 2007)

Just read through this, is sorta similar...at least with the high compression. Any relation maybe?

http://www.nissanforums.com/ga16de-1-6l-engine/86188-compression-test-results.html


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## Altima SSS (Oct 10, 2007)

zakgord said:


> *Results I posted in another forum after my compression test...*
> 
> 
> *A few questions...*
> ...



Too high of compression isn't due to the oil squirts you put in the cylinder. The oil test just helps to seal rings IF they are leaky. As the link in your post above show, it's could be lots of carbon build-up.

Doing the compression test without opening the throttle shouldn't give you lower numbers IF you cranked it over long enough to make the compression test gauge stop increasing. Opening the throttle all the way just takes less engine revolutions to get to the same max pressure result on the gauge.

It's strange that the compression would go to 220 ~ 240 psi on cyl 3 and 4 after adding a few squirts of oil. Maybe these two cylinders have much more carbon build-up than the others, and when the oil was there to seal it made the pressure higher.

A leak down test is really the best way to see the condition of the rings and valves.

Maybe do the compression test again with a helper that opens the throttle all the way and cranks the engine while you watch the gauge ... have the helper crank the engine until the gauge doesn't increase any more. I'd try this first to just verify you have accurate results for all cylinders. If you were doing this alone, did you have sight of the gauge? If so, then I guess you could redo the test with the throttle wide open.

Your dry test results aren't too far off from what the spec calls out ... 178 psi.
http://www.autozone.com/images/cds/gif/large/0900823d801b6074.gif

I'd do the test without using the oil, but do the test just after the car has been driven as that will ensure some oil on the cylinder walls to help give you a more accurate test.


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## zakgord (Jun 11, 2007)

Thanks for the reply. 

I did the test with my dad, so had two people. I read the gauge while he cranked the engine. I watched it rise a bit more with each stroke until it reached its peak noted psi. Would that carbon buildup affect idling or even cause my misfire? Seems like I still have some other problem as the code reads misfire on cyl 2, and the highest compressions appear on cyl 3 and 4. So, who knows? I might try running a bunch of fuel/carbon cleaner through and/or using premium gas with a bit of hard driving to try and burn it off just for the heck of it.

I did a quick spray of carb cleaner around the top of the exhaust manifold gasket...no noted smoothed idling. So, I dont think the leak there could cause this problem...although I didnt get under the car to spray the under side of the gasket.

I may just end up leaving it be and seeing how long I can go on this engine. There really isnt anything wrong with it while driving around, and if it aint broke dont fix it....right?


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## zakgord (Jun 11, 2007)

Also, do I have the order of cylinders right? The one closest to the belts is cylinder 1 and the one near the distributor is cyl 4, right?

I have read a few places on boards where it seems like they are saying the opposite.


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## Altima SSS (Oct 10, 2007)

zakgord said:


> I did a quick spray of carb cleaner around the top of the exhaust manifold gasket...no noted smoothed idling. So, I dont think the leak there could cause this problem...although I didnt get under the car to spray the under side of the gasket.


Did you mean the intake manifold gasket? Spraying around the exhaust manifold gasket won't tell you anything.



zakgord said:


> Also, do I have the order of cylinders right? The one closest to the belts is cylinder 1 and the one near the distributor is cyl 4, right?
> 
> I have read a few places on boards where it seems like they are saying the opposite.


I believe the Haynes manual shows cylinder #1 on the belt end of the engine.


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## zakgord (Jun 11, 2007)

No, I meant the exhaust manifold gasket because thats where I noticed the smoke leaking from... at least it appeared to be coming from the joint between the manifold and the head. I suppose nothing would change by spraying the exhaust gasket becuase there is no vacuum pressure there....I was just hoping i'd get lucky and the leak there would be the cause of my misfiring...o well.

Should I try letting some gas additive/fuel system cleaner sit overnight or a few hours in my cylinders to try and eat away any possible carbon buildup. This is what someone in my linked forum suggested for their high compression/ carbon buildup problem.


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