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Throw this out.

If a valve spring broke, could the damper that's inside the spring hold the valve closed just enough to show good compression, but prevent full sealing when car is running?

Or, maybe the other question is what type of valve springs you running? Single coil?
 

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Discussion Starter · #64 ·

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Discussion Starter · #69 ·
its not a leak down test. its a quick easy way to find where tf the compression is going.

or do whatever you want
What you call easy is not so for me. To pop the vc's; I have to undo hoses (boost), throttle cable, upper intake, alternator and wires, remove fuel lines, undo cold side piping, and on and on. I'd rather do a proper leak down test to identify any issues before I start pulling everything back apart. Thanks for the advice though.
 

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What you call easy is not so for me. To pop the vc's; I have to undo hoses (boost), throttle cable, upper intake, alternator and wires, remove fuel lines, undo cold side piping, and on and on. I'd rather do a proper leak down test to identify any issues before I start pulling everything back apart. Thanks for the advice though.
Turn off fuel, sit in the car with door open, crank for 10seconds while listening.

Same rhythm, is sign of relative similar compression. A distinct speed up, change in rhythm, you have a compression problem.
 

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What you call easy is not so for me. To pop the vc's; I have to undo hoses (boost), throttle cable, upper intake, alternator and wires, remove fuel lines, undo cold side piping, and on and on. I'd rather do a proper leak down test to identify any issues before I start pulling everything back apart. Thanks for the advice though.
it aint going to fix itself. you verified you have spark, fuel, injector, noid etc and your problem is lack of compression. vcs are coming off whether you like it or not.
 

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Discussion Starter · #74 ·
it aint going to fix itself. you verified you have spark, fuel, injector, noid etc and your problem is lack of compression. vcs are coming off whether you like it or not.
Here's where I'm at... while idling; I pulled #5 injector plug and heard no difference in idle nor did the tach show a drop. Yet; the cylinder is reading the same temp as the others when I shoot it with a temp gun. It's things like this that make me hesitate to take everything apart just yet. I've been hot rodding for 40 plus years and never have I had so many issues with runability until I got into 5.0 Mustangs.
Yes; I'm whining. :(
 

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Hi all, I am still new to the forum but not new to fixing vehicles. Here is my 2c worth.

A lot of things have been tested or replaced and known to be good. What I have not seen answered is if the head gasket is possibly bad between cylinders? depending on when valves are open I think it could be possible to still build full compression with a failed head gasket between cylinders.

This is fairly easy to confirm good (or bad), do the cylinder leak test by pushing air into the cylinder in question, rotate engine until the valves for that cylinder are shut, listen for leaks, next pull the spark plugs from adjacent cylinders, if the head gasket is bad between cylinders it will be pretty obvious when those plugs are pulled.

Good luck
 

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Discussion Starter · #76 ·
Hi all, I am still new to the forum but not new to fixing vehicles. Here is my 2c worth.

A lot of things have been tested or replaced and known to be good. What I have not seen answered is if the head gasket is possibly bad between cylinders? depending on when valves are open I think it could be possible to still build full compression with a failed head gasket between cylinders.

This is fairly easy to confirm good (or bad), do the cylinder leak test by pushing air into the cylinder in question, rotate engine until the valves for that cylinder are shut, listen for leaks, next pull the spark plugs from adjacent cylinders, if the head gasket is bad between cylinders it will be pretty obvious when those plugs are pulled.

Good luck
Good idea. I'm working on the leak down.
 

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If the cylinders are not firing, you would not have similar temps at the header compared to the others. Didn’t you say you have compression, spark, fuel, AND exhausts temp?
 

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Discussion Starter · #78 ·
If the cylinders are not firing, you would not have similar temps at the header compared to the others. Didn’t you say you have compression, spark, fuel, AND exhausts temp?
I agree. That's why I'm baffled. Should I see or hear a drop in idle if I pull a plug wire or the injector plug? You'd think so. I can't tell if all cylinders are getting proper fueling without having the injectors tested. I can, however, tell if each injector is activating.
 

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Here's where I'm at... while idling; I pulled #5 injector plug and heard no difference in idle nor did the tach show a drop. Yet; the cylinder is reading the same temp as the others when I shoot it with a temp gun. It's things like this that make me hesitate to take everything apart just yet. I've been hot rodding for 40 plus years and never have I had so many issues with runability until I got into 5.0 Mustangs.
Yes; I'm whining. :(
What’s the temp of the cylinders? The two bad ones and good ones.
 
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