compression test question
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Senior User
Joined: Aug 2012
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From: thornton CO
compression test question
I'll be removing the valve covers this weekend and I want to do a compression test while I'm in there. I have searched the forum and found info on the adapters needed but can't find a clear description of the procedure. Can anyone point me in the right direction?
Postmaster
Joined: Apr 2012
Posts: 2,613
Likes: 8
From: North Georgia
One at a time... WITH VALVE COVER HARNESSES UNPLUGGED...
Remove a glow plug... thread in the adapter... connect to compression gauge... crank engine over a few turns...
If your connections are good.. and dont leak down... you should see the highest point of compression achieved on that cylinder.
Rinse and repeat for all 8.
The cheap 5$ grease gun hose at harbor freight threads into the glow plug port on the 7.3 very nicely... then a double female 1/8th inch coupler to thread on the other end... then your compression tester quick connector fitting with scrader valve...
Easy peasy.
Remove a glow plug... thread in the adapter... connect to compression gauge... crank engine over a few turns...
If your connections are good.. and dont leak down... you should see the highest point of compression achieved on that cylinder.
Rinse and repeat for all 8.
The cheap 5$ grease gun hose at harbor freight threads into the glow plug port on the 7.3 very nicely... then a double female 1/8th inch coupler to thread on the other end... then your compression tester quick connector fitting with scrader valve...
Easy peasy.
Fleet Mechanic
Joined: Mar 2009
Posts: 1,856
Likes: 52
From: Sacramento Delta, CA
Funny you should ask. I am doing the compression test on my passenger side tomorrow or this weekend.
Christof13T is the man, but there may be something of use in the following:
https://www.ford-trucks.com/forums/1...sion-test.html
Also see Post #57 and Post 58 in this thread:
https://www.ford-trucks.com/forums/1...up-pipe-4.html
This may also help. I printed this out and wrote my readings on it:
And this scared me:
Christof13T is the man, but there may be something of use in the following:
https://www.ford-trucks.com/forums/1...sion-test.html
Also see Post #57 and Post 58 in this thread:
https://www.ford-trucks.com/forums/1...up-pipe-4.html
This may also help. I printed this out and wrote my readings on it:
And this scared me:
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Senior User
Joined: Aug 2012
Posts: 307
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From: thornton CO
I thought I would post results of my testing. Please tell me not to be concerned.
1. 290
2. 298
3. 285
4. 298
5. 290
6. 295
7. 285
8. 295
At least they are all close to the same but they all seem really low for the mileage. I know the numbers change at this altitude, but they still seem low, which seems crazy to me. When I first got the truck I was able to retrieve all the service records for it and the maintenance schedule was followed pretty good. Their was a K&N sticker on the intake box but the filter was stock and the clips on the box were good, and the compressor wheel looks great.
Feed back as always is much appreciated.
1. 290
2. 298
3. 285
4. 298
5. 290
6. 295
7. 285
8. 295
At least they are all close to the same but they all seem really low for the mileage. I know the numbers change at this altitude, but they still seem low, which seems crazy to me. When I first got the truck I was able to retrieve all the service records for it and the maintenance schedule was followed pretty good. Their was a K&N sticker on the intake box but the filter was stock and the clips on the box were good, and the compressor wheel looks great.
Feed back as always is much appreciated.
Fleet Mechanic
Joined: Mar 2009
Posts: 1,856
Likes: 52
From: Sacramento Delta, CA
Others will know better than me how to interpret your numbers, but you may want to provide some additional info. Did you have a battery charger attached when you compression tested? I.e., was it cranking strong throughout the test? How many times did you count for the cylinder's to turn over before accepting the reading? Did you test each cylinder more than once? (I know mine went up the second time I tested them, presumably because the rings became coated with oil the second try but were dry the first time around).
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Senior User
Joined: Aug 2012
Posts: 307
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From: thornton CO
I did not hookup charger but the cranking speed was the same throughout. I counted 7 turns on each cylinder and I only tested once. I tested cylinder 2 twice (2 is where I started) it was the same as the first time so I stopped. And the oil temp when I started was about 190*.
Post Fiend
Joined: May 2009
Posts: 5,470
Likes: 3
From: Pea Ridge, AR
Was this on a warm or cold motor?
Is this a recently rebuilt motor with low miles still before break-in?
Probably not too much to be concerned with, but they are low...are you certain the gauge is accurate? Also altitude can play some role, but I am not sure to the amount of compensation, I would have to look into that, being that the air is less dense.
Edit: Here is a compensation factor chart that I found which assuming you may be around higher altitudes you would be on par.
These would be accurate for around 60 degrees Fahrenheit.
500ft = 0.987
1500ft = 0.960
2500ft = 0.933
3500ft = 0.907
4500ft = 0.880
5500ft = 0.853
6500ft = 0.826
7500ft = 0.800
8500ft = 0.773
So if you were wanting a goal of 350psi and you were at 5500ft your new goal would be 298.55psi, so looks like you are on par and all within specifications.
Is this a recently rebuilt motor with low miles still before break-in?
Probably not too much to be concerned with, but they are low...are you certain the gauge is accurate? Also altitude can play some role, but I am not sure to the amount of compensation, I would have to look into that, being that the air is less dense.
Edit: Here is a compensation factor chart that I found which assuming you may be around higher altitudes you would be on par.
These would be accurate for around 60 degrees Fahrenheit.
500ft = 0.987
1500ft = 0.960
2500ft = 0.933
3500ft = 0.907
4500ft = 0.880
5500ft = 0.853
6500ft = 0.826
7500ft = 0.800
8500ft = 0.773
So if you were wanting a goal of 350psi and you were at 5500ft your new goal would be 298.55psi, so looks like you are on par and all within specifications.
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Postmaster
Joined: Apr 2012
Posts: 2,613
Likes: 8
From: North Georgia
Temp when he started was 190*...
Warm motor...
All 8 below 300?
Even at 2k ft i would think they should be higher...
Any blowby?
Smoke?
What kinda shape is your oil in?
Take a look at your compressor wheel... look sanded on the edges?
Are your egt's under control?
Warm motor...
All 8 below 300?
Even at 2k ft i would think they should be higher...
Any blowby?
Smoke?
What kinda shape is your oil in?
Take a look at your compressor wheel... look sanded on the edges?
Are your egt's under control?
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Thread Starter
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Senior User
Joined: Aug 2012
Posts: 307
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From: thornton CO
I did the test because I needed to replace the driver side vc gasket so I would have it open anyway. I've also had a couple guys tell me that it looks like I have some blow by after looking at my ccv hose, but when I turn over the oil fill cap it doesn't bounce at all, it just stays put.
It is the original engine unless the p.o had it replaced by someone other than the ford dealership. But I got the service records from the dealer.
My oil has less than 4k miles on it.
The compressor wheel looks good.
The truck smokes a little when I get on it in 80e and 100p, more in 100p. I can also get exhaust temps to 1200*+ in 100p but I thought that was normal. On the highway in 80e at cruising speed (65-70mph) it stays between 650 and 800*.
I am at 5200 ft.
It is the original engine unless the p.o had it replaced by someone other than the ford dealership. But I got the service records from the dealer.
My oil has less than 4k miles on it.
The compressor wheel looks good.
The truck smokes a little when I get on it in 80e and 100p, more in 100p. I can also get exhaust temps to 1200*+ in 100p but I thought that was normal. On the highway in 80e at cruising speed (65-70mph) it stays between 650 and 800*.
I am at 5200 ft.
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