96 Cobra. Low compression on 3 cylinders. Please Help.

L_Santi7

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What’s up everyone. Ok so this may be a long winded post. I’ll try and keep it short. Thanks guys for reading if you do.


So I bought my 96’ Cobra a few months ago. Car was a 1 owner and has 15k original miles. From what I know the engine is stock with a Vortech Supercharger. No other internal mods done. When I first went to go test drive the car it had a slight tap under the drivers side valve cover (nearest the firewall) that has gone away from time to time when the car heats up to operating temp.


So a few weeks ago I took the car to get the tune checked and upgrade a few things to bring it up to date. The gentleman who I brought it to said the car has low compression in cylinders 6,7,& 8. (75,89,75) Now the dude is extremely knowledgeable and has a great reputation. However I’d like some input on what it may be. He’s saying could be a cracked piston. Maybe stuck rings.


Now the car sat from 2016-2020 when I purchased it. It was on a tender and started from time to time but not much from what the previous owner said. And it wasn’t started at all for the last year.


Car only smoke from time to time out of the tailpipes under full throttle. Nothing while idling and has plenty of power. It’ll hesitate every now and then but for the most part it runs solid. Had some blowby where some smoke comes out of the oil cap when removed.


Any suggestions? Thank you guys ahead of time for helping me out.
 

white95

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That’s tough. Unfortunately, you’re not going to have any definitive answers until you tear it down for inspection.

If it otherwise seems to run fine, perhaps you should consider building a short block in the mean time. Have the heads freshened up while it’s down and enjoy many more years of worry free service.

…or Coyote swap it :cool:

I know that’s unlikely but I’m an extremist :)
 

apsmith49921

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Cylinders 7 and 8 are notorious for ticking because if failed valve guides due to coolant dead heading. It's extremely possible with the extra power and heat the made the problem worse. As someone else said until it's torn down you won't know. It's possible you can get away with rebuilding the heads. I would have them do a leak down test also that will help determine a little bit more before you tear it apart.

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lwarrior1016

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Do the leak down test, but if the rings are stuck or piston cracked, the leak down results may come up skewed.

If you are getting blow by, that is compression in the crank case. That comes past the rings. Either burnt/broken rings, or busted ring land.

Plan for an engine rebuild. In that list, put forged pistons and a head cooling mod.
 

L_Santi7

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That’s tough. Unfortunately, you’re not going to have any definitive answers until you tear it down for inspection.

If it otherwise seems to run fine, perhaps you should consider building a short block in the mean time. Have the heads freshened up while it’s down and enjoy many more years of worry free service.

…or Coyote swap it :cool:

I know that’s unlikely but I’m an extremist :)

Hahaha! Trust me I’ve already started comparing a Coyote swap vs a rebuild. Eventually I plan on building the motor after I found this out. I was just hoping to get at least a summer out of it before I put it away and tear it apart.
 

L_Santi7

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Cylinders 7 and 8 are notorious for ticking because if failed valve guides due to coolant dead heading. It's extremely possible with the extra power and heat the made the problem worse. As someone else said until it's torn down you won't know. It's possible you can get away with rebuilding the heads. I would have them do a leak down test also that will help determine a little bit more before you tear it apart.

Sent from my SM-G988U using Tapatalk

A leak down test was performed by the shop I took it to which turned out no good. I guess I’m just hoping it’s the rings being stuck since it sat for so long. I guess time will tell.
 

L_Santi7

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Do the leak down test, but if the rings are stuck or piston cracked, the leak down results may come up skewed.

If you are getting blow by, that is compression in the crank case. That comes past the rings. Either burnt/broken rings, or busted ring land.

Plan for an engine rebuild. In that list, put forged pistons and a head cooling mod.

Yea like I said above. It was performed and came back no good. I’ve since pulled the plugs and added Marvel Mystery oil to each cylinder in hope that of it is something like a stuck ring maybe it’ll come loose and reseal. I’ve heard great results from this method and I figured I’d give it a shot. Going to let it sit for a few days and see what happens.
 

Zutz23

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Don’t feel so bad man, my car was running mint last week, was out for a cruise with the wife and the. All of a sudden a timing chain jumps and takes out cylinders 3-4. Now I have to do a rebuild as well. I’m not mad about it because now I can build it the way I want.

I’m pissed because covid prices and lack of parts will out my car out for a year :( and summer just started.


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white95

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Don’t feel so bad man, my car was running mint last week, was out for a cruise with the wife and the. All of a sudden a timing chain jumps and takes out cylinders 3-4. Now I have to do a rebuild as well. I’m not mad about it because now I can build it the way I want.

I’m pissed because covid prices and lack of parts will out my car out for a year :( and summer just started.


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You have my luck it seems.
 

L_Santi7

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Hey man, trying the oil won’t hurt anything. It’s better to try it than just give up.

Yea. Definitely not giving up on it just yet. Just frustrated because I bought the car with intentions of enjoying it before I tore into it but it is what it is. Checked the oil in the cylinders today and 6 and 8 had a little in it and 7 had no oil. Poured a little more to let it soak some more. We’ll see what happens.
 

L_Santi7

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Don’t feel so bad man, my car was running mint last week, was out for a cruise with the wife and the. All of a sudden a timing chain jumps and takes out cylinders 3-4. Now I have to do a rebuild as well. I’m not mad about it because now I can build it the way I want.

I’m pissed because covid prices and lack of parts will out my car out for a year :( and summer just started.


Sent from my iPhone using Tapatalk

Yea that sucks dude. I guess it could always be worst right. At least mine is somewhat drivable other then one of the valve cover gaskets leaking which causes oil to drip a little onto the manifold and smoke. Just really can’t beat on it. I’ll replace that gasket and baby it until July when the car is due to go in to have the motor pulled. Good luck with the rebuild.
 

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