Compression test

markweatherill

markweatherill

markweatherill

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I just did a compression test on my car.
The results were between 219 - 224 PSI.
But I realised afterwards I hadn't held the throttle open while doing the test, and you are, like, supposed to, I know.
Perhaps I'll have another go tomorrow and do it properly. In the meantime are these numbers at all meaningful?
 
They aren't that high...I had ~190PSI (13BAR) on two pistons...but then that's 15BAR and to be honest...a very high reading. Mine were meant to be 11.5BAR or so. :p
 
It's a Nissan Rasheen, JDM import, 1500cc engine like an Almera. The book says 13.24BAR / 192PSI is good.
Would a closed throttle give a reading higher than expected, or lower..?
 
to be honest your looking really for consistency across the readings as they are above 140psi*.

having the throttle open or closed doesn't make much of a difference you might just have to crank a little longer before the gauge tops out.


*depending on engine.
 
Dogbreath said:
Closed throttle will give a lower reading. Some compression testers (cheap ones!) have shockingly inaccurate gauges though.
Click to expand...

Very much so, they are guides really and not accurate.

2-3 cranks should see full compression. I did it without the throttle as that's what both the car's book and the gauge instructions said.
 
The throttle doesn't seal like an inlet valve does so unless you actually let the engine start (which you shouldn't, disconnect the crank position sensor to stop the engine firing) it will make absolutely no difference whether it's closed or open.
 
Shad said:
The throttle doesn't seal like an inlet valve does so unless you actually let the engine start (which you shouldn't, disconnect the crank position sensor to stop the engine firing) it will make absolutely no difference whether it's closed or open.
Click to expand...

It can make a difference; on my Fiat Coupe I see about 10-15 PSI difference between open and closed throttle.
 
Shad said:
The throttle doesn't seal like an inlet valve does so unless you actually let the engine start (which you shouldn't, disconnect the crank position sensor to stop the engine firing) it will make absolutely no difference whether it's closed or open.
Click to expand...

engine shouldnt be in a position to start anyway, you should test with all plugs out.
 
Main thing is they are all even more than the actual reading, as above the guage may be inaccurate.
Why did you do the compression test?
 
i would expect a 30psi from a hot/cold test, have never seen more then 5 or so psi variation from a throttle open/closed!

but i suppose it could come down to how well the iac and breathers are working.
 
mewonders if there is some liquid in the bores giving the rings a better seal (ala 'wet test' of dropping a bit of oil down the plug holes)

Did you take the fuel pump fuse out and run the engine till it died?

Maybe its fuel flooding thats giving a better than normal ring seal elevating the reading?
 
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