Compression levels don't seem right..
New User
Joined: Apr 2002
Posts: 14
Likes: 0
From: Mesa United States
Compression levels don't seem right..
Just rebuilt a 76' 360 complete and it's running rough at idle, and won't pass the emmisions test for " Idle " hydrocarbons. We've checked everything and replaced everything but the EGR valve and it still runs terrible at idle speed. We removed the hose from the EGR valve and it does run a little better, but the idle is still extremely rough. We were going to replace the EGR valve, but we decided to do a compression check. All but one of the cylinders is between 118 and 120-- but one, #6, is at 109.. maybe even between 108 and 109. Obviously that's not right, right?
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
Compression levels don't seem right..
That's fine. A little variation between cylinders is to be expected. A rule of thumb is that the lowest cylinder on a healthy engine shouldn't be any less than 85% of the highest. Your highest is 120. 85% of that is 102.
New User
Joined: Apr 2002
Posts: 14
Likes: 0
From: Mesa United States
Compression levels don't seem right..
Okay. The variation is acceptable. But, all but one of them are around the same psi. One at 109. Doesn't that seem odd? Only one cylinder is in a different range-- and this is a new rebiult engine.
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
Compression levels don't seem right..
All sorts of things could account for the variation. My bet is variations in combustion chamber volume. It's not uncommon for the chambers to vary by +/- 2 or 3 cc. Did you have them cc'd when they were rebuilt?
