jdgleason
Active member
I thought it would be a good idea to put a thread together on compression testing. It's a common practice in working on these trucks, but seems like a lot of the general population doesn't get to see it.
A compression test is really pretty simple, the biggest thing is getting the glow plugs out for the test itself. This will apply to almost any motor (aside from glow plugs in a gas application obviously). Compression testers themselves are really simple. Basically it is just a gauge that has a fitting to thread into a glow plug or spark plug hole into whatever head you desire. There are different gauges for different engines, but the concept is universal. Oh, most will have a pressure bleed valve as well.
First step will be pulling all the glow plugs. The idea behind pulling the glow plugs us so that other cylinders aren't building pressure during your test. Also, the compression tester will use the glow plug port to measure pressure.
Once you've got the glow plugs pulled, it's time to figure out what you are going to use to actuate the starter. For us 6.4 owners, we have it east. Ford built a lead right into the battery harness. Touch that to hot side of the battery and it's game on. If you're doing this cab on, make sure the ignition is off.
Here's a picture of how I had mine set up today.
Once that's done, time for the test itself. Thread the compression tester in the glow plug hole finger tight. Make sure you can see the gauge and start cranking the motor over. Let it turn over 5-10 times or until it stops building pressure.
Quick picture of how this one was set up. Not the best pic, but you can see the hose disappear into the valve cover.
Now that you have numbers, you can see a couple different things.
A.) Peak number will tell you the health of the cylinders/rings/valves. For this 6.4, anything from 340-375 psi indicates a pretty healthy motor.
3.) Relative compression is good to know also. Ford says that if the high number to the low number are within 75% of each other, then all is well. Seems a little loose to me, but what do I know.
I took a quick video to help summarize.
http://www.youtube.com/watch?v=jFX3M-B1hxw
A compression test is really pretty simple, the biggest thing is getting the glow plugs out for the test itself. This will apply to almost any motor (aside from glow plugs in a gas application obviously). Compression testers themselves are really simple. Basically it is just a gauge that has a fitting to thread into a glow plug or spark plug hole into whatever head you desire. There are different gauges for different engines, but the concept is universal. Oh, most will have a pressure bleed valve as well.
First step will be pulling all the glow plugs. The idea behind pulling the glow plugs us so that other cylinders aren't building pressure during your test. Also, the compression tester will use the glow plug port to measure pressure.
Once you've got the glow plugs pulled, it's time to figure out what you are going to use to actuate the starter. For us 6.4 owners, we have it east. Ford built a lead right into the battery harness. Touch that to hot side of the battery and it's game on. If you're doing this cab on, make sure the ignition is off.
Here's a picture of how I had mine set up today.
Once that's done, time for the test itself. Thread the compression tester in the glow plug hole finger tight. Make sure you can see the gauge and start cranking the motor over. Let it turn over 5-10 times or until it stops building pressure.
Quick picture of how this one was set up. Not the best pic, but you can see the hose disappear into the valve cover.
Now that you have numbers, you can see a couple different things.
A.) Peak number will tell you the health of the cylinders/rings/valves. For this 6.4, anything from 340-375 psi indicates a pretty healthy motor.
3.) Relative compression is good to know also. Ford says that if the high number to the low number are within 75% of each other, then all is well. Seems a little loose to me, but what do I know.
I took a quick video to help summarize.
http://www.youtube.com/watch?v=jFX3M-B1hxw
