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post #14 of (permalink) Old 11-10-2018, 05:04 PM
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Join Date: Dec 2010
Location: Pine, CO
Posts: 117
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Wait a minute. Why does everyone think the engine is toasted? Gas expansion with heat comes to play here. At sea level a compression of 350 PSI divided by the heat of expansion from air (Aprox 1.4) divided by the atmospheric pressure gives us a compression ratio of 17:1. The 7.3L has a compression ratio of 17.5:1 so the numbers are close. Move this baby to 7500 feet ASL and the numbers 250/1.4/17.5=10.2 atmospheric so the numbers are again close. Consider the fact that on a standard day the atmospheric pressure at 7500 feet is around 11.1 psi.

So we plug in 11.1*17.5*1.4=271 PSI. So a 250 PSI compression check at 7500 may be a little low but I don't think the engine is toast. Something else may be amiss; ie. slow cranking speed, etc.

I think the problem may be worn injectors. He states the problem is reduced power when cold. I assume that it runs and has normal power once warmed up. I would not give up on this engine just now. Injectors could be at fault.


2002 F250 XLT, Super Cab, Short Bed 4X4
Build Date: 10/1/2001
7.3 PSD, 6 Speed Manual Transmission
AIS Severe Duty Intake
20.1 MPG Average
Pine Junction, Colorado

Last edited by rv6a; 11-10-2018 at 05:19 PM.
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