Compression Test how too??? Specs? (1 Viewer)

[PirateMcgee]

I searched but could not find. How do you do a compression test on an fj60? I've only done fuel injected vehicles before so how can I easily/quickly crank over the engine without dumping fuel into it? or breaking anything lol?

What is the factory range/specs?

I'm thinking about picking up an fj tomorrow and want to check the compression first.

Thanks,
Scott

 

[Butt Ugly Chuck]

I've never worried about the fuel. Pull the plugs and take the coil wire off. Start at one end and work to the other. Record numbers as you go. For constency between measurements, I count cycles and keep them the same for each test - say 10 cycles for each cylinder - you'll be able to hear it. Spec compression is between 114 and 149 psi with no more than 14 psi difference between each cylinder.

Others have suggested doing a leakdown test, but I'll let someone else chime in about that as I've never done it.

Good luck!
Butt

 

[PirateMcgee]

me neither.....


so do I pull all the spark plugs at once or one at a time?

 

[Butt Ugly Chuck]

Pull them all and keep them in order in case you want to compare any odd commpression results to spark plug appearance.
Butt

 

[2mbb]

The engine should be warmed up to operating temperature. I've been taught to disconnect and ground the coil wire. The battery should be fully changed. For best results, open the throttle wide open. With the throttle closed, air flow is restricted. Also with the throttle open, less gas will get dumped in. remove all the plugs. test one cylinder at a time. I usually crank for four or five compression strokes, but as said above, try and do each cylinder the same number. I find a remote starter switch very useful for this test. I hook it up to the starter motor contacts. I can crank the engine while holding the compression tester.

The absolute value of each cylinder is not as important as the comparison between cylinders. All the values should be pretty much the same, within 10% or so of each other.

 

[PirateMcgee]

thanks alot!

hope this all goes well.....I really want to get it.....

 

[Wile E Coyote]

I've been taught to disconnect and ground the coil wire.

Yuppers, ground the coil wire. It keeps the coil happy.

 

[NocalFJ60]

I don't see any reason to ground the coil line vs. not grounding it. It probably would not hurt anything but with no resistance to ground it seems like the coil would see full current and might get hot? I guess if it is not grounded and you get close to the coil with something while doing the test then it could arch. The FSM says to disconnect the high tension cord from the ignition coil to cut off the secondary circuit." I take that as just removed the wire from coil to the distributor. I think the first time I did it without a manual to be safe I pull the plastic piece off the end of coil and took the two wires off the coil that power it.

 

[augirthedude]

leak down test

The leak down test measures the percentage of compressed air applied to a cyl. that leaks out of the cyl. on the compression stroke. You need to have a compressed air source and the leak down device(tool) I got mine from the snap-on man 20 years ago. A very usefull tool to determine the condition of an engine. Be aware that carbon build-up on the valves can lead to false readings on this static test. Pulling the valve cover and tapping the apropriate valves for the cyl. you are testing will dislodge the carbon. You must also have a way to hold the crankshaft from turning while the compressed air is applied the the cyl. being tested or get the piston to just exactly TDC (for that cyl.) . Which can be tricky unless you do this all the time. Watch the breaker bar that you will have on the front crankshaft pulley bolt. When the compressed air is applied during the test and depending on which side of TDC you are on, the breaker bar will have a quite a bit of force on it and can loosen the crank bolt if the crank spins in the right direction and or skin or bruise your fingers ..... on second thought just do a compression test.