Hi All,

I need to carry out a compression test on my 93' WRX, but just want to make sure on the best method of doing this.

I realise that all the plugs need to be removed first of all, and for the most accurate results the engine should be warm and the throttle wide open, but do I need to do anything else in preparation for the test? Do I need to cut the fuel supply or is this not really an issue? Obviously would rather not spray fuel everywhere if it's a possibility!

Also If anyone can let me know what sort of figure I should be looking to see for a healthy engine.

Cheers!

 

personally would pull the crank sensor connector

 

should have added you should see around 140-150 BUT within reason dont worry about the figure as long as they are similiar

 

is it better from hot or cold?

 

best is to do both and you get an idea of where a problem lies

 

Great thanks, had thought about pulling the crank sensor (I do this for oil changes to dry crank), but wasn't sure if it cut fuel or ignition. I assume there's no need to disconnect the coilpacks themselves from the loom? I'm running newage coilpacks.

 

just the crank sensor

 

Just to tie this thread up for any future readers, I carried out the test on my car using a draper pressure tester (£20 from Ebay, seems good quality for the money!), from cold as was worried to run the car until I had some sort of results to look over.

I removed all plugs first and disconnected the crank sensor as per Alyns suggestion, I did each test on wide open throttle and recorded the following;


Drivers side rear - 170psi
Drivers side front - 165psi

Pass. side rear - 169psi
Pass. side front - 169psi

A bit high but assuming this is due to the engine being cold.

Doesn't look bad considering the car has 201,000km on the clock :-) My misfire turned out to be a loose coilpack.

 

Normally the numbers are lower on a cold engine

 

better to do leaking down test

 

I dream of those number and that compression.
I have a 04 Sti with 100k on it and the engine has never been split and I've wore the engine out.
10 months ago I did a comp test and was 100psi on all cylinders as suspect engine tiredness then just after mapping making 435hp @ 1.5bar on a Gt3076.
After that done countless track days, Nurburgring trip plus a time attack event and still going.
Had it mapped again Saturday gone by martyn @ engintuner and she's dyeing even more.
Wanted to try push on toward 500 but it wouldnt make more than 1.5 and now dropped to 400hp so lost 35hp at same boost.
I've yet to do another comp test to see what's on but it still starts good and doesn't smoke at all so we think exhaust valve area must be fried in one way or another.
I've got an all day track pass from MCR for spring action day up castle combe so she's not getting retired yet 😁

Cheers

 

lol, that's impressive! If yours has taken all that abuse at 100psi then I should probably stop worrying about my engine being high mileage! My cars running 280bhp at the most I'd say so gets an easy time of it!

Fingers crossed yours holds up at Castle Combe, though it sounds like it doesn't like giving up so I've no doubt it'll survive!