How to do a compression test on a diesel? - Ford Truck Enthusiasts Forums



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How to do a compression test on a diesel?

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Old 10-30-2009, 09:56 AM
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How to do a compression test on a diesel?

I'm trying to figure out how to do a compression test on my 6.0. When moving down the road, when I come to a stop, occationally my truck will sound like it has a really bad miss. I accelerate, and it goes away, but it stays while i'm stopped, and it feels really bad. It doesn't happen often, but when it does the truck shakes all over, like it's running on 7 or even 6 cylinders. Has anyone ever had this? It still accelerates fine when I give it gas though.

I'd appreciate any input on this, I'd hate for the unthinkable to happen to my beloved 6.0... And keep it a secret from the 7.3 and v10 guys , i bust their chops from time to time , I'm sure they'd love this one.
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Old 10-30-2009, 11:23 AM
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First things first check for codes.A lazy/bad injector can cause your symptoms,so can the FICM.The compression can be checked through the glow plug hole a PITA.
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Old 10-30-2009, 08:49 PM
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start truck pull oil fill cap and see if it smokes like a fright train. If not most likly not a compression issue.
to awnser your question you need a compression test that is for diesel engines. DO NOT use one for a gasser.

the best test to start of with in this case would be a crankcase pressure test.
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Old 10-30-2009, 08:56 PM
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You can buy a fairly cheap pressure/vacuum gauge from any auto parts store. Hook up some tubing/hose to it and connect it to your dipstick tube. If the tubing/hose is long enough to run into the cab, you can drive it around and see what your crankcase pressure is under WOT.

Ford's spec for the crankcase pressure is 15 mmhg or 0.29 psig.
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Old 10-31-2009, 02:00 PM
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Jut a question here if you are smoking out the crankcase what would you think is the problem most likely ie... Bad ring or a fried piston. I'm asking cause mine is doing that. I'm putting in a different motor, but I plan to rebuild the one that is in the truck now. What kind of compression should I see out of these trucks. I guess I should check the cylinders before I take it out so that I know where the problem is
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Old 10-31-2009, 03:44 PM
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I think they are all going to smoke somewhat. It really is the pressure that determines if you have a problem or not.
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Old 10-31-2009, 05:43 PM
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most all gauges read a little bit different. but a normal around 385 psi. Its important that you do the compression test correctly though.
the right ways is to remove all 8 glow plugs, crank engine over with the key off (to do this use a remote start or crank from the terminal next to the right battery) this is done to clear the cyclinders of oil/fuel.
once this is done install the compression tester and crank the engine over 5 times (5times only this will provide the most accurate reading).
hope this helps
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Old 03-23-2014, 01:02 AM
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Quote:
Originally Posted by bismic View Post
You can buy a fairly cheap pressure/vacuum gauge from any auto parts store. Hook up some tubing/hose to it and connect it to your dipstick tube. If the tubing/hose is long enough to run into the cab, you can drive it around and see what your crankcase pressure is under WOT.

Ford's spec for the crankcase pressure is 15 mmhg or 0.29 psig.
bismic,
Do you know where I can find a gauge that has a large enough scale to show that # accurately?

Do you also know the ID of the tubing which I imagine has to slip on the outside of the dipstick tube?

Thanks.

Last edited by kayooh; 03-23-2014 at 01:10 AM. Reason: .
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Old 03-23-2014, 08:59 AM
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Quote:
Originally Posted by run6.0run View Post
That's funny Dom,,

Yeah,, I understand anything can be overlooked.

Here's a bunch of videos leading up to pulling the engine.

6.0 Powerstroke compression test - YouTube



What do you guys think this stuff is on the injector?

6.0 powerstroke possible engine - YouTube

Pulling the engine tomorrow.

Btw,, Corey is here and we are gonna swap his engine too. Finally gonna get that Blackwater one out of there.
Check out the first video. Maybe that'll help ya.
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Old 03-23-2014, 09:40 AM
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Originally Posted by npccpartsman View Post
Check out the first video. Maybe that'll help ya.
Did he have to take the fenders off to do this test?
Please tell me where exactly did he plug that flexible hose connected to the compression gauge?
The video is kind of dark and the camera was moving too fast.

Thanks.
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Old 03-23-2014, 10:02 AM
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Quote:
Originally Posted by kayooh View Post
Did he have to take the fenders off to do this test?
Please tell me where exactly did he plug that flexible hose connected to the compression gauge?
The video is kind of dark and the camera was moving too fast.

Thanks.
You take the fender liners, glow plug harnesses, and glowplugs out to do compression test. You might send run6.0run a PM to see exactly where he got his compression tester.
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Old 03-23-2014, 10:23 AM
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Not going to be a compression issue if the issue clears up under acceleration.

ICP sensor or pigtail
Bad Injector

I have been chasing a similar symptom in a friend's truck. Random idle surge when hot. Swapped ICP and EBP sensors, verified ICP pigtail integrity etc. Finally it threw a #5 pending contribution code, polished the spools on the passenger bank and it helped, but did not totally eliminate the random surge.

You need a scanner that can pull pending codes.

Josh
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