Dirk Miller

LOOKING FOR THE ACCEPTABLE PROCEDURE TO ISOLATE CYLINDERS ON LS3 FOR LEAK DOWN TEST OF CYLINDERS

Does anyone know the proper way to isolate cylinders on an LS3 to do a leak down compression test?

Today, I tried pulling the fuse to the ECM, but this also de-energizes the push button key module and I cannot turn the engine over.
I was then about to pull the eight individual electrical connections to each coil, but thought I should check with others that have successfully done this. The electronics on this car are so sensitive that I want to be extra careful not to screw things up and I hope to find out what others have done first.

Any ideas?

envirotrans

No such thing as a ( leak down compression test)
A compression test is done by removing the spark plugs and using a compression gauge in each plug hole and cranking the eng over to get a reading in each cylinder one at a time.
a leak down test is performed by putting air pressure into a spark plug hole when the piston is at top dead center and listing to where the air comes out if leaking by the rings, intake or exhaust valves, it is also used with a differential pressure gadge set

mgarfias

I think he's thinking what my best friend was taught in Ford Mechanic school as a "power balance" test. They'd stuff a test light into the plug boot and ground out the plug wire. Find a cylinder that when you do this the engine doesn't run any crappier, and thats your dead cylinder.

flink

IR thermometer pointed at the exhaust manifold will find a dead cyl.

fatbillybob

Use FAA certified leakdown testor
Know your firing order
Find TDC
Add air pressure read leak at gauge
Car in high gear
Rock car forward to next cylinder in the firing order
Add air pressure read leak.
Compare lead % over all 8.

Compression test gauge
All plugs out
Screw in gauge
Trigger starter with remote starter
Read compression psi
Screw in gauge next cylinder and repeat

FASTFATBOY

Take the rockers off that cylinder to make it 100% effective.

Dirk Miller

Nice to hear you guys don't mind to much if I ask a few ignorant questions.

I actually want to perform a general compression test on each cylinder. Can anyone tell me if I will throw a check engine light if I just disconnect all eight electrical leads to my eight independent coils and crank over? I first tried pulling the fuse to the ECM but I could not turn the engine over from the drivers seat. (I do have a remote starter switch, but have not hooked this up to the starter with the fuse pulled). I don't want to throw any codes.

envirotrans

Get or make a remote stater switch, hook up to the starter and use that to turn over the eng, you need at least 5 turns cranking to get full compression, and block the gas pedal open to get max air into the cylinders. Make sure the transmission is in park or neutral with the wheels blocked.
If you get any codes just unhook the battery wait 5 minutes and hook it back up and go for a drive so ECM can relearn

Dirk Miller

Ok. I'll use your suggestions, including unhooking battery if needed. Thanks

Now for my remedial 101 question....My C6 has no key, but instead it has a push-button ignition switch. Now that I will be connecting my remote starter switch to the starter, should I first try pulling the ECM fuse again so engine does not fire up? Or should I just disconnect all eight leads to the eight coils and crank over while testing each cylinder?
Again, the electronics on this car are pretty elaborate and I just want to keep this as simple as possible.

wstaab

Remove all 8 spark plugs.
Remove the fuel pump fuse.
The engine will not run with the fuel pump inoperative.
Install a compression gauge in the spark plug hole for the cylinder you want to test.
Hold the accelerator pedal wide open crank the engine for 5 or 6 revolutions.
Do not pull the fuse for the ECM or you can not hold the throttle blade wide open.
Best results is with a warm engine but if you want to test with a cold engine spray a little WD40 in the cylinder before you test it.

Dirk Miller

Thanks
this is what I was hoping to hear

envirotrans

All of the above...