Really low compression
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Senior User
Joined: Sep 2003
Posts: 254
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From: Colorado
Really low compression
I messed up my engine real good over the weekend 
I ended up sucking a bunch of water into it while it was running (went through some water that was a bit too deep). My compression used to be 140 all round, now it's around 90. From what I've read, it sounds like I bent the rods.
I haven't put it back on the road yet because I still have to flush the transmission. But the question: will 90 compression even move the truck? It's an 88 Bronco, 351w. Thanks guys.
I ended up sucking a bunch of water into it while it was running (went through some water that was a bit too deep). My compression used to be 140 all round, now it's around 90. From what I've read, it sounds like I bent the rods.
I haven't put it back on the road yet because I still have to flush the transmission. But the question: will 90 compression even move the truck? It's an 88 Bronco, 351w. Thanks guys.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
that is very low. are you sure the rods are bent. if you have a bad head gasket or stuck valves this could also give a low compression reading. best bet would be to pull the motor and take it apart and inspect everything. if it looks bad replace it. are you sure all the water is out of the motor?
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Joined: Sep 2003
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From: Colorado
I'm pretty positive all the water is out. After I towed it home I drained the oil and took out the spark plugs. I hand cranked out the water, put some WD-40 in the cylinders and let it sit overnight. The next morning I cranked it with the starter, a little more water vapor blew out. I let it sit until that evening and then put the plugs back in and fired it up. It sounds the same at all RPM's as it did before, no wierd vibrations or anything.
I just did a running compression test, I disconnect the fuel injector at one cylinder and I got 120 psi while the engine was running. What does this mean? I'm also a bit confused how a stuck valve would just lessen compression, because the cylinders do hold the air once it's in there.
I'm in agreement that the engine needs to be pulled, I've been wanting to put in a roller cam for a while, so I may as well just do it now. But do you think it's driveable like this until I can get to that (won't be for a for weeks)?
thanks for the input
I just did a running compression test, I disconnect the fuel injector at one cylinder and I got 120 psi while the engine was running. What does this mean? I'm also a bit confused how a stuck valve would just lessen compression, because the cylinders do hold the air once it's in there.
I'm in agreement that the engine needs to be pulled, I've been wanting to put in a roller cam for a while, so I may as well just do it now. But do you think it's driveable like this until I can get to that (won't be for a for weeks)?
thanks for the input
Junior User
Joined: Jun 2004
Posts: 81
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what i would do is run some oil in there and hand turn the motor over . i have goten a motor out of a junk yard that had low comp.. i ran tranny fliud throug the carb while it was running and it help alot... try some thrust pint oil in the cyld.your comp should come back up if you bent a rod you would know it for sure....bad vib's noise from bottom end like wise.....hope you have some good luck ....
