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HELP! low compression on all cylinders

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Old 03-02-2012, 12:51 AM   #1
1989dangeroustoy
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HELP! low compression on all cylinders

I have a 96 explorer 4.0 ohv, today I did a compression test and got about 90 psi on all cylinders, I don't know if its bad rings, valves or timing chain, also I think I may have a cracked head, what do you guys think? Also do you think I'd be better off buying a used motor or rebuilding mine, I'd rather not pull the motor out and I definitely do not want to rebuild the bottom end
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Old 03-02-2012, 08:29 AM   #2
Dono
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Low on all cyl? You sure your compression testers reading right? Run OK? How many miles on the motor? If it's really that low across the board, and mileage is high you might want To consider a complete rebuild or rebuilt motor.




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Old 03-02-2012, 09:48 AM   #3
yavapaires
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Originally Posted by 1989dangeroustoy View Post
I have a 96 explorer 4.0 ohv, today I did a compression test and got about 90 psi on all cylinders, I don't know if its bad rings, valves or timing chain, also I think I may have a cracked head, what do you guys think? Also do you think I'd be better off buying a used motor or rebuilding mine, I'd rather not pull the motor out and I definitely do not want to rebuild the bottom end
My main question is; how did you check the compression? Did you pull all the plugs, or one at a time? Did you hold the throttle open, or closed? Improper procedure can affect the reading. If you have 90psi all cylinders, and the engine is running smooth, with good power, I wouldn't be too worried.
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Old 03-02-2012, 10:22 AM   #4
my98nnj
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Ditto above, plus the test is more accurate on a warm engine.
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Old 03-02-2012, 10:37 AM   #5
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Try testing one cyl and see the read. Then squirt some motor oil into cyl and re test. If pressure goes up I believe that it would indicate rings.

Side note when you do restart it there will be lots of oil smoke. Neighbors won't like it. let it burn off before you hit the road or you could get stopped and cited.




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Old 03-02-2012, 02:53 PM   #6
1989dangeroustoy
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I tested. It cold with all the plugs out and throttle
Closed
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Old 03-02-2012, 02:54 PM   #7
1989dangeroustoy
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I tested. It cold with all the plugs out and throttle
Closed , motor has 143xxx on it
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Old 03-02-2012, 02:56 PM   #8
1989dangeroustoy
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It runs but I have a cylinder 4 misfire
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Old 03-02-2012, 03:51 PM   #9
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You need to check one cylinder at a time. You do not have to pull out all of the spark plugs while you test that one cylinder. Just unplug the coil to prevent the truck from starting. Do what DaExplorer said and put a tablespoon of oil into the cylinder and then immediately retest. IF the compression goes up with the oil in the cylinder, chances are your top oil ring is bad and your losing compression.




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Old 03-02-2012, 06:09 PM   #10
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You will not get an accurate reading with pulling one plug at a time. However, I have done that to check a single cylinder. And the top two rings are compression rings. The lowest rings(three piece) are the oil control rings.
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Old 03-02-2012, 06:50 PM   #11
1989dangeroustoy
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OK so I did get a lot better reading with the engine warmed up ,I got around 120 psi, but now I'm stumped. I checked the plug, wire, and coil, has decent compression , and i still have a misfire ,all that's left is the fuel injector or a small pissing coolant leak into the cylinder any other suggestions?
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Old 03-02-2012, 09:08 PM   #12
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You will not get an accurate reading with pulling one plug at a time. However, I have done that to check a single cylinder. And the top two rings are compression rings. The lowest rings(three piece) are the oil control rings.
Maybe I'll learn something new here. Why will pulling all the plugs give more of an accurate reading than pulling one plug at a time? Each cylinder is independantly sealed and thus have the potential of giving a different compression reading on each one. How is pulling every plug to do the test going to make it more accurate?




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Old 03-02-2012, 09:37 PM   #13
rjcooperss396
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It doesn't make it any more accurate. It simply allows the other cylinders to bleed off pressure so that the engine turns faster and the reading is higher. I've never pulled all the plugs nor opened the throttle to do a compression test on any of my vehicles.

The only thing you need to make sure of is that you do the same thing for each cylinder. Don't open the throttle for one but then don't for another. The thing you are checking is if all the cylinders are around the same.
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Old 03-02-2012, 11:15 PM   #14
budwich
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you probably need to give the forum more info on the misfire and checks that you have performed. Is it during cold starts, warm start, warm runs...etc

further, did you swap plugs (cylinder to cylinder), like-wise wires, like wise coils (side to side)?????

Further, what does the plug from that cylinder look like compared to others?
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Old 03-02-2012, 11:34 PM   #15
1989dangeroustoy
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Its a constant misfire from start to operating temp, Cel throws a po304 cylinder 4 misfire, I got all new plugs autolite platinums. I checked the plug wire with a spare plug wire and a spark testing light, I swapped wire 3 and 4 on the coil pack all with no change, compression test was all cylinders around 120 psi, no coolant loss no excessive smoke, slight sweet smell if you put your nose close to the tailpipe but you really have to smell for it! All plugs looked the same and normal
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Old 03-04-2012, 01:27 AM   #16
1989dangeroustoy
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Anybody?
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Old 03-04-2012, 01:53 AM   #17
bilzy7
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I had p0304, it was just a bad plug, coil pack/plugs/wires... Maybe the plug socket(whatever it's called) has a problem. But p0304 is for crap... If I remember right cylinder 4? I know it is on drivers side.
Google that code. I found so many other forums/sites with information on it. Goodluck.




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Old 03-04-2012, 01:54 AM   #18
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You confirmed correct gap on all plugs? .054 if I'm not mistaken or is that for the OHV engine...




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Old 03-04-2012, 06:43 AM   #19
gonenuke
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Might be a plug bad out of the box, happens sometimes.




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Old 03-04-2012, 05:40 PM   #20
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Well, we have air, gas, compression, and spark to make the cylinder fire.

Clogged injector maybe?




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