low compression in #6 cylinder 5.0 help

[sourgrout]

Hey peeps I have a 1990 5.0 with low compression in the number 6 cylinder it reads 35lb were the others read 125lbs. This motor has 113k miles and is stock. Anybody know what it might be? just some ideas would help before i go pullin the motor. Thx

[351wStang]

Does it have a miss? It may be an intake valve hanging open. Hope its not a head gasket leak. Does it smoke? The rings may have gone bad in the #6 cyl. You will hear a misfire if your exhaust valve is hanging open. It could be any number of things.

[motor_head_429]

I agree with 351wStang, I would check the head, and the head gasket, and if that doesn't work, then it could be the rings.

[StangNut86]

i assume you mean 125 PSI? that's way too low. i'm guessing you have problems starting and such.

my 4-banger makes 100, 75, 0, and 100 PSI in that order. it doesn't even start and will not stay running even when i try dropping the clutch.

i would suggest rebuilding this motor of yours w/a little bit better internals, and while you're at it change your heads and such. sounds like it's nearing the end of it's life span.

[rerun]

actually 125psi isn't that low. it is in the range of running good (but LITTERLY on the bottem).. you have one dead cyl, which is no big deal if its just a beater that you use, but if you race it, or want a perfectly running car then you would want to rebuild it anyway.

[SkylineUSA]

Check to see if its the ring or the head. Either way, you might as well go for a rebuild with that many miles on it.

[351wStang]

Blame it on the last 13k. I had $13 in my pocket the day I rolled my dad's car. But I was also doing 95mph in a 35mph zone, it started raining and the car wouldnt hold the road in a turn. So maybe it was just my fault? LoL, Young and Dumb!

[rerun]

Originally Posted by 351wStang

Blame it on the last 13k. I had $13 in my pocket the day I rolled my dad's car. But I was also doing 95mph in a 35mph zone, it started raining and the car wouldnt hold the road in a turn. So maybe it was just my fault? LoL, Young and Dumb!

what kind of car was this?

[SkylineUSA]

Originally Posted by rerun

what kind of car was this?

A Totaled Car

[MagicRat]

Originally Posted by 351wStang

Does it have a miss? It may be an intake valve hanging open. Hope its not a head gasket leak. Does it smoke? The rings may have gone bad in the #6 cyl. You will hear a misfire if your exhaust valve is hanging open. It could be any number of things.

Try a cylinder leak down test. Find a spark plug adaptor to put some compressed air in the cylinder when the piston is at TDC with the valves closed. Be careful the engine won't roll over and put about 100 psi into the cylinder. Listen for escaping air out the intake, exhaust, rad cap or oil filler cap to see where the leak is. This might save you an unnessary repair.