compression values
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Senior User
Joined: Feb 2020
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compression values
Ok...'84 f250 6.9idi, 2wd, t-19. Is there any place I can look at some compression values to get an idea on where my engine is at? What are they on a new idi? What would they be on an engine on its last legs? Would like a range to go on. Thx much for replies...want to know if I should spend any more $$ (new IP, injectors, GPs, return lines etc) on the old truck, or cut my losses...
Fleet Mechanic
Joined: Sep 2016
Posts: 1,519
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From: Nevada
400 - 500psi on a good healthy engine. probably that when new.
here are some threads I came across searching.
https://www.ford-trucks.com/forums/1...-question.html
https://www.ford-trucks.com/forums/1...-question.html
You can do the compression test your self saving some money by going to a shop.
HF Has a compression tester, lots of threads on their tester. Some of the early testers
that were suppose to work, the adapter didn`t fit. They have improved on their kits.
Here is a thread from OB on modifying it.
https://www.oilburners.net/threads/d...success.69771/
Charlie
here are some threads I came across searching.
https://www.ford-trucks.com/forums/1...-question.html
https://www.ford-trucks.com/forums/1...-question.html
You can do the compression test your self saving some money by going to a shop.
HF Has a compression tester, lots of threads on their tester. Some of the early testers
that were suppose to work, the adapter didn`t fit. They have improved on their kits.
Here is a thread from OB on modifying it.
https://www.oilburners.net/threads/d...success.69771/
Charlie
Scope Wizard
Joined: May 2019
Posts: 6,530
Likes: 25
Compression test
To perform a compression test on this engine, you need to have a diesel compression gauge and a glow plug adapter. Remove all the glow plugs to check any cylinder. Crank the engine at least five revolutions and the same number of revolutions for each cylinder. It would probably be a good idea to have a battery charger hooked up during the test. Ford lists no compression specs for these engine, only stating the lowest cylinder should be no more than 25% lower than the highest cylinder, with a low to high comparison chart showing a range of 195 to 440 PSI. In reality the compression should be at least 350 psi.
To perform a compression test on this engine, you need to have a diesel compression gauge and a glow plug adapter. Remove all the glow plugs to check any cylinder. Crank the engine at least five revolutions and the same number of revolutions for each cylinder. It would probably be a good idea to have a battery charger hooked up during the test. Ford lists no compression specs for these engine, only stating the lowest cylinder should be no more than 25% lower than the highest cylinder, with a low to high comparison chart showing a range of 195 to 440 PSI. In reality the compression should be at least 350 psi.
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Senior User
Joined: Feb 2020
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Ok Lonewolf and Charmalu, good info...will be enough to determine what course I take after I do a compression test...will post the numbers...FWIW, there are an unknown number of miles on the engine, and no maintenance records either... This will give me a baseline on how far to go on the engine before rebuilding or trading it in at one of those "drag it, drive it, push it in" events at car dealer...BTW..crawled under truck to photo the FSV...looks like a leak is going on under there...probably the source of my problems...Hope it is...was not looking forward to $$$ R+Ring the IP, injectors,etc... Edit: And a good time to do a compression test is when one is replacing GPs....
Lead Driver
Joined: Apr 2008
Posts: 6,945
Likes: 13
Ive seen 7.3s with 350 that run fine, also seen a 6.9 run like **** that had 450. Compression isnt everything, what youre looking for most is consistancy. The closer the numbers the better, altitude influences the numbers a LOT
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