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Old 05-06-2008, 12:04 PM   #1 (permalink)
lockeal
lockeal
 
Join Date: Oct 2006
Location: State College, PA
Drives: 91 3000GT SL
Trader Rating: (1)
lockeal is an unknown quantity at this point
Default Effects of Heads with compression difference = 35 psi?

I had a cracked head on my 91 DOHC so I bought a rebuilt one and had the other one rebuilt by a local shop. The car has a hesitation/miss under low load for the first 15-20 minutes of driving and then is fine.

My compression #'s in PSI:

Cylinder Warm Engine With oil added
1 175 190
2 150 185
3 170 ---
4 155 200
5 180 ---
6 145 190

All are above the min 139 psi in the manual. However, the 35 psi compression difference from high to low is well above the 14 psi limit in the book. It doesn't say what will happen if there is this large difference like this? Will this cause the hesitation when cold?

As the low compression increases with the addition of the oil, it indicates bad rings/piston but they looked fine with cross hatch and everything.

Thoughts?
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