Low compression #7
Thread Starter
Pro
Joined: Jan 2002
Posts: 741
Likes: 9
From: Rancho Cordova CA
Low compression #7
I have an unhappy car. Sunday after I installed my headers I bounced off my rev limiter during a short race. Monday the car was running rough, I changed plugs and checked wires last night to no avail. Tonight I checked the push rods, none were bent, then I started a compression test and found #7 has only 60 Lbs. 1,3, and 5 have 159 160. I have not checked the other side yet too bummed. I did poor oil down the plughole and rechecked. I did not see an increase in compression. I hope it is only a bent valve of bad head gasket. I read that it may be a ring even though I did the oil test. I will pull the heads this weekend. I may try a leak down test first. :sad: :sad: :sad:
Melting Slicks
Joined: Jan 2001
Posts: 2,635
Likes: 2
From: Aloha, Oregon
Re: Low compression #7 (Steve'01)
how ironic...#7 is the slug i tourched a hole in last summer!! well, with only 60psi compression test, you either have a bent valve or broke a piece of the piston land off (like i did). do a leakdown with compressed air. you'll know immediately what it is. if you hear air coming out through your TB, its an intake valve. if you hear air rushing out your tail pipes, its the exhaust valve. If your oil dipstick pops out of its shaft, uh oh!!! the hole in my piston allowed enough air to the bottom of the engine to literally shoot my dipstick out. Hope for the best!!
Former Vendor
Joined: Aug 2001
Posts: 5,798
Likes: 50
From: Dallas & Chicago TX & IL
Re: Low compression #7 (Steve'01)
I had a similar problem on cylinders...#4 and #8. We checked everything and found to be the bottom end as the culprit causing a crazy 70hp lost. Well, we replaced the block with one out of an F-body with 10k. :auto: At first I couldn't believe that this block gave up so easy...My 5.0 mustang went through a lot more before giving up the ghost. :boxing
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Re: Low compression #7 (Myhardtop)
Hopefully it is only a valve. Last time I had that low of compression it was on 1,5, and 4 and they were all cracked pistons..chunky style! At least your guage is consistantly off. Should be reading 195-200 on each cylinder.
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Thread Starter
Pro
Joined: Jan 2002
Posts: 741
Likes: 9
From: Rancho Cordova CA
Re: Low compression #7 (Closer_2001)
Did the leak down test tonight. At first I thought the air was going into the intake, but no such luck. It was coming out of the dipstick and around the holes in the heads where the push rods go through. The piston must not be tore up because I still have some compression and she still runs fair. At first I was very bummed almost sick, but need to look at the way the rest of you have, good reason to beef it up. Oh well, tomorrow I plan my new bottom end. Thanks for the words of encouragement. Too bad I sold that extra car. :steering: Not
