Compression Question

jpjeep26uk

jpjeep26uk

YJ Enthusiast
Joined
Nov 12, 2022
Messages
273
Location
UK
Hi all. Tested the compression on my 4 cylinder 2.5 and these are the results:
Cyl1 - 129
Cyl 2 - 125
Cyl3 - 130
Cyl4- 145

Tried it a few times, they all report the same.
Is this good or bad?
Still trying, after 8 months and some £2000 later, to even get it to start and run properly. Cranks fine, sparks fine, just won't fire and stay fired and the two occasions it did it ran terribly. Had to shut it down due to smoke complaints from neighbours.
Are the compression numbers indicative of something? Thanks all.
 
By the manual, you shouldn't have more than 10 psi (I think may be 15 or something) difference between each cylinder, so technically bad, but I wouldn't think twice about getting numbers like that from an older engine. Those aren't so far off that I would expect poor running due to compression.
 
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DOWNS said:
By the manual, you shouldn't have more than 10 psi (I think may be 15 or something) difference between each cylinder, so technically bad, but I wouldn't think twice about getting numbers like that from an older engine. Those aren't so far off that I would expect poor running due to compression.
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That's great, thanks for confirming.
 
DOWNS said:
By the manual, you shouldn't have more than 10 psi (I think may be 15 or something) difference between each cylinder, so technically bad, but I wouldn't think twice about getting numbers like that from an older engine. Those aren't so far off that I would expect poor running due to compression.
Click to expand...

Do you know what would make the oil presdure gauge show virtually zero when I flick the key to 2nd notch? Before my troubles began, it used to sit juuuuust to the left of middle and then once it fired up it would move to just past middle. Literally put 3.8l of oil in last weekend.
 
jpjeep26uk said:
Do you know what would make the oil presdure gauge show virtually zero when I flick the key to 2nd notch? Before my troubles began, it used to sit juuuuust to the left of middle and then once it fired up it would move to just past middle. Literally put 3.8l of oil in last weekend.
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If the engine isnt' running it should show 0.
 
DOWNS said:
If the engine isnt' running it should show 0.
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OK that makes sense. When I do manage to fire her up she runs like a dog and the pressure needle only goes about a quarter way up.

When she ran sweet, it sat at half way and then surged up a bit when I drove her faster. Now I can't even get her 6ft off the drive.
 
On the plus side, 1/4 way up the oil pressure gauge is 20 psi which is great at idle. FSM lists 13 psi as minimum pressure at idle. FWIW mine barely reads 5 PSI at idle :ROFLMAO: But that could just be a sender that's not quite in spec.
 
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I’ve mentioned this on here before, but I’m going to again, if you want an accurate reading use a mechanical gauge. Same goes for H2O temp.
 
DOWNS said:
On the plus side, 1/4 way up the oil pressure gauge is 20 psi which is great at idle. FSM lists 13 psi as minimum pressure at idle. FWIW mine barely reads 5 PSI at idle :ROFLMAO: But that could just be a sender that's not quite in spec.
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Ah, OK, that's good then. Finally something actually reads correct haha. Now if I could just get the fuel gauge to show at least a sign of life. It used to! Not brilliant but at least it showed some gas in the tank. Got about $60 in there and not a jot! Like a Steely Dan song...
 
ytradio said:
I’ve mentioned this on here before, but I’m going to again, if you want an accurate reading use a mechanical gauge. Same goes for H2O temp.
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Agreed, i basically use it to confirm I HAVE pressure not necessarily an accurate one.

My oil analysis always comes back good even with the amount of noise my poor little 2.5 makes.
 
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DOWNS said:
Agreed, i basically use it to confirm I HAVE pressure not necessarily an accurate one.

My oil analysis always comes back good even with the amount of noise my poor little 2.5 makes.
Click to expand...

Do you have a 2.5 as well? Any chance you could post a picture of your fuel line connections to the back of the throttle body? I only ask as when I was running a fuel.pressure test, the fuel came pouring out of the left pipe and I read the fuel should come in via the right hand pipe, as you look from the front of the hood.
 
jpjeep26uk said:
Do you have a 2.5 as well? Any chance you could post a picture of your fuel line connections to the back of the throttle body? I only ask as when I was running a fuel.pressure test, the fuel came pouring out of the left pipe and I read the fuel should come in via the right hand pipe, as you look from the front of the hood.
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I have a 95 which has port injection. I saw that post but didnt have the info to give you for the Renix TBI
 
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