I was wondering something...why is it that the compression readings seem to climb with each crank of the motor? If the exhaust valves are opening and releasing all pressure, I would have thought the compression reading would always be the same.
Example...readings on my 7.3L showed average 220/310/410 on the first 3 strokes. Another member commented that this was a decent reading.
Does it have something to do with the rings "seating" themselves or sealing up?
BTW, I understand the basics...2 side by side low readings usually indicates a bad head gasket, consistant low pressure may indicate worn valves etc. But the original question kind of stumps me...how do you differentiate between worn rings and what I was showing?
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91 F350 7.3L ZF-5 Speed 4.10 New Project Truck and lots to learn!
Also Own:
95 Freightliner FL70 5.9L Cummins (inframed at home) 6 speed Fuller, 11R22.5, 4:10, 4" exhaust and stack with a teeny weeny muffler [img]/ubbthreads/images/graemlins/smile.gif[/img], 14,000lb Stellar Hooklift for lifting waste containers
81 F350 351M C6 4.10 14 Yard Dump Body and 6mpg!
98 Dodge Cummins 5.9L-12V 5 Speed 4.10 LS 3500 Dually 4x4, 420,000 on odo, Chelsea PTO pump, 12K winch, 14 yard Dump Body, worn out shift knob and driver seat, no silencer, Boost, Pyro, no muffler, gutted kitty, lots of mud.
I don't know, maybe it does have something to with the rings/oil being squirted up there [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/confused.gif[/img]
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Travis
Will Work For Diesel Fuel.
The hose of the compression gauge has a one way check valve in it, and the gauge only has so much time to react to the pressure increase. It will continue to rise until it reaches equallibrium. At that point the actual cylinder pressure is displayed on the gauge.
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95" Extd Cab F250HD 4x4 DRW, /86"6.9 T19 GV o/d 3.73 axles, Hypermax Pulse turbo, intercooled / Modified Hypermax ram air induction, PowerShot 2000 LPG system "first design". Ride rites @ all 4 corners, Dana 50 mono Beam up front, Ford 10.5" in rear with 4 wheel disk brakes. Other Truck, 1983 IHC "S" with 14ton NoMar wrecker body, 30,000 GVW, 229"wb with a 340hp 6V92TA, Eaton Roadranger 13spd RTO9513, 3.70 ring & pinion and LPG kit. Alcoa 22.5x8.25 with Michelin XVE 255x70x22.5
Since I just went through this stuff with mine here is what the book says.
In order to properly read compression you must turn the engine over six times. If you build compression within the first two or three strokes it is OK, if it takes all six to build good compression you have bad rings. If you build no, low or mid compression every stroke you have a bad valve/head gasket/etc.
Yours is Oh Tay, good.
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Tim the toolman Harris
1993 F-350 excab, home made stainless running boards, Z-5 tranny, Tires 235/85/16, 410 rear gear, running gear all new, new injectors on 3-06 code D, reinstalled my ATS TC4305 turbo I rebuilt myself, 3 inch downpipe with 4 inch back and out the side in front of the rear tire, 175,000 miles. Leather seats from a 2002 F 150. http://community.webshots.com/album/548525045nyuVni
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