Weak Cylinder ?
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Tuned
Joined: Aug 2002
Posts: 299
Likes: 2
Weak Cylinder ?
ah, i believe its modified and my local mechanic told me it had a weak cylinder. i just replaced the plugs wireds distributor cap and bought a new coil. i haven't been able to test it because i'm restoring the body right now. i don't know anything about motors so i don't really wanna mes with it to bad. any ideas????
Post Fiend
Joined: Jan 2003
Posts: 10,323
Likes: 2
From: Montana Territory
Weak Cylinder ?
Go find a 400 and transpolant that into it. Everything you have already put on the M is interchangeable, come to think of it its interchangeable between the three. hehehe
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Tuned
Joined: Aug 2002
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Posting Guru
Joined: Feb 2002
Posts: 2,404
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From: Cleveland, WI USA
Weak Cylinder ?
When he said "weak cylinder", I'm assuming it means low compression. 3 people I know got the same vague diagnosis. When I tested the compression, the "weak cylinder" indeed had very low compression.
To do a cheap and easy diagnosis, buy or rent yourself a good compression gauge from Autozone or the like.
- Remove all the spark plugs and pull off the coil wire.
- Put the comp. tester in the spark plug hole on the 1st cyl., and have someone turn the engine over a few times.
- Write down the reading.
- Repeat this for every cylinder.
The difference between readings should be no more than 5 psi apart. If you have one that is really low, do the following.
- Retake the compression reading just to be sure.
- remove the comp. tester and spray or squirt a little oil or wd40 into the plug hole.
- Take the compression reading again, and compare it to the last one.
If the compression goes up, you have a piston ring problem. If it doesn't, it could be a valve problem. The oil will help seal the rings a little, but won't help seal the valves.
Good luck.
Kevin K.
To do a cheap and easy diagnosis, buy or rent yourself a good compression gauge from Autozone or the like.
- Remove all the spark plugs and pull off the coil wire.
- Put the comp. tester in the spark plug hole on the 1st cyl., and have someone turn the engine over a few times.
- Write down the reading.
- Repeat this for every cylinder.
The difference between readings should be no more than 5 psi apart. If you have one that is really low, do the following.
- Retake the compression reading just to be sure.
- remove the comp. tester and spray or squirt a little oil or wd40 into the plug hole.
- Take the compression reading again, and compare it to the last one.
If the compression goes up, you have a piston ring problem. If it doesn't, it could be a valve problem. The oil will help seal the rings a little, but won't help seal the valves.
Good luck.
Kevin K.
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Elder User
Joined: Jun 2003
Posts: 886
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From: Houston/Hope BC
Weak Cylinder ?
No, there is NOTHING you can do for it except drive it like a blue-hair. Everything wears out dependant on run-time and load...minimize these. (You were hoping for some miracle pour-in cure or "ring seal in a can" I bet... don't waste your money.)
Posting Guru
Joined: Dec 2002
Posts: 2,003
Likes: 2
From: chicago burbs
Weak Cylinder ?
i'd just like to add if it was or wasn't stated that during comp testing the throttle should be blocked open to allow air to the cylinders, and the coil wire should be pulled from the dist cap and grounded so the high voltage has a path to terminate.
Posting Guru
Joined: Dec 2002
Posts: 2,003
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From: chicago burbs
Weak Cylinder ?
a cylinder leak down test is a little better for diagnosing the exact cause of the weak cylinder. it involves pressurizing the cylinder through the spark plug hole with air. the air can be heard through the intake manifold/carb indicating a bad intake valve, or through the exhaust pipe indicating a bad exhaust valve, out the valve cover indicating bad rings, out a different plug hole or bubbles in the radiator indicating a bad head gasket. if a bad valve is found, repair can be limited to only the offending parts if need be for budget reasons, and i believe head gaskets can be purchased in singles also if you want to do a minimum repair.
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