How to do a compression test on your engine 

I was about to go and rent the tool from them too lol thats why I was watching this video. guess I'm not going to anymore

There should be a Schrader valve (like the valve stem on your tire) in the hose. Someone (probably whoever rented it last) likely removed it. Without that valve, any pressure the engine builds will be gone as soon as the valves open, and you'll get a zero reading.

Sometimes it happens that the previous renter didnt report an issue with the tool, to avoid getting charged for it. That happened to me with a torque wrench at autozone. I went back and mentioned the issue and they gave me another that worked fine.

Couldn’t have been user error!! 😂

Tool was obviously broken

not me.. my car is misfiring and thats why im here.

@@lilgagey3889😢

There's two schools there. If you warm the engine first, letting things have a chance to seal up, you're getting a reading at operation, yes but, if you do the test cold, you actually can find out what's worn or wearing. I want to know if the rings are just starting to wear or the valves are carboned up and need to be "blasted." Doing it with a hot engine just tends to mask the problems you're trying to find. I'm an ASE engine performance and drivability tech and I came up in the old school world of actually finding any mechanical issues rather than try to cover them up. An engine always gives up its secrets and runs the worst when it's cold... And that's when you find out what lays ahead. :)

Pressure test should be done on cold engines.

Please explain more my brother!! My compression was a lot higher but all consistent with each other just after 5 compression strokes. And after the test The 5.2 will not start now. Did I f^__ something up.l disconnectied coil to safe place but not fuel?? Lost here my friend!! Montana Rick.

3 month old comment but it has to be motor oil. You don’t want to contaminate the oil with solvents.

Figure out what's caused the drastic drop in compression. It could be something as simple as a blown head gasket, or something... Less simple, like significantly pitted bore on that cylinder

Boy I should have grabbed the drink before bringing it to my mechanic, that hurt my wallet

@@professionalgenny5096 sorry to hear that.

@@professionalgenny5096 Oof, been there...

You are 100% correct. Always remove all the plugs, have a good battery to crank the motor and have your throttle wide open. Maybe Cooley thinks he knows, but doesn't really know.

@@johnnybonacci7114 CORRECT, both of you, I also put a battery charger on my battery while performing the test. HE DOESN'T REALLY KNOW, LMAO.

On carburated motors do u take off mechanical fuel pump before test ? Or just leaave on and test ?

@@jonhromeo6108 To me the most accurate way on a carbureted engine is simply to remove the carb intself. But as it may be a pain to do, unplug the the pump intake line fist. Then let the engine die. After that you can perform the test. Be sure that you maintain WOT and also that the cold start device would'nt mask the carb air intake during cranking operations. Best result if you remove the air filter. Cheers

Vaporised gas, can disturb results as gasoline has a tendency to wash the cylinder liners oil compound when no ignition occurs. Results may vary between a dry or a wet cylinder.

Disconnect the fuel inlet from carb, put a tube on it and put the other end into a portable gas tank (so you save that gas) As far as your distributor, disconnect the connector that leads into the HEI. This prevents any spark from being created.

Cool Thanks 👍

why holding the accelerator?

Clear flood mode, prevents car from starting

That's ok if you remove the injectors cables, otherwise the catalytic converter won't like it.

The petrol will spray inside cylinder.

Perfectly normal.

To calculate the compression pressure you need to multiple the compression ratio by atmospheric pressure then add the atmospheric pressure to your multiplied result eg if you have a compression ratio of 9 to 1 and a atmospheric pressure of 14.7, 9x14.7 =132.3 +14.7 =147 psi , also I would look up how to carry out a compression test properly

Dylan, If you have a rubber hose somewhere ( AFTER THE PUMP ) crimp it off with vice grips & rubber hose over the teeth. Or disconnect the steel fuel line ( AFTER THE PUMP ) & add rubber hose to it ( WITH HOSE CLAMP ) then run it into a bucket.

Please​@@NoWr2Run

Google what your particular engine is supposed to be. My honda is 220 across the board lol

thats a hello no there -- 10-4

The reading is accurate for that test condition. BUT please be AWARE that leaving the plugs out with everything else connected. Will mean the injectors squirting fuel, the pistons pushing that spray out of the engine in the mist of spark plugs doing what they do best, putting out a spark. With that in mind remember that gas spray and spark is usually a dangerous combination... ;-)

Jesus Moya that will alter your compression reading slightly. Fuel doesn’t compress.