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Old August 17th, 2019, 13:38
bad_idea bad_idea is offline
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Join Date: May 2016
Location: Virginia
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Diagnosing a Bum 2.5L

Hi All!

I have a 90 MJ with 2.5L and a 5 speed. I paid $400 for it and drove it on the trailer. Previous owner says the truck has sat since 2016 when the radiator leaked out and overheated.

I started tearing into it today. Swapped a good radiator into it. Runs a bit rough but runs, drove it up and down the road - has decent power. Blows smoke out of the valve cover. The CCV system is fully operational. Did a compression test - #1 - 120, #2 - 150, #3 - 165, #4 - 30. I did the compression test with the engine cold. I added a bit of oil to #4 cylinder and still got 30 PSI. I'm guessing something is catastrophically wrong with cylinder #4. What says you all?

I would like to fix it if I can cheap. If not then I'll let the truck sit until I can find a decent SBC to swap into it.

Thanks for the help.
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Old August 17th, 2019, 20:01
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old_man old_man is offline
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Join Date: May 2003
Location: Loveland, Colorado
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Re: Diagnosing a Bum 2.5L

agreed hopefully only a valve
Tom Houston - Former Colorado Chapter President, current Treasurer , Terminal Adrenaline Junkie, and Rocket Scientist
Loveland, Colorado My teardrop build
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Old September 30th, 2019, 09:29
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CMNCHE CMNCHE is offline
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Location: Pennsylvania
Posts: 353
Re: Diagnosing a Bum 2.5L

Pull the valve cover and see whats going on up top. Could be a bent pushrod, bad valve, missing rocker. Or it could be more serious. Wont know until you open it up.
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