When doing a compression test on a 7.3 do you... - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

 
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post #1 of 2 (permalink) Old 08-11-2008, 01:21 AM Thread Starter
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When doing a compression test on a 7.3 do you...

After reading some scary stories of Compression numbers, I realized I never tested mine. Had 122,000 mi when I got it, has 184,000 mi now. Runs fun but you never know.
Anyways, when testing on these motors, all GP's out, is it best to disconnect the main UVCH connector or each injector connector when doing the test. Is there anything else that needs to be DC'd for the test? Was stock compression 400psi or 450psi?
Thanks

Truck:
Early 99 F-350 (99.5+Conversion)
Lariat Crew Cab Long Bed
05'-07' Front End/08' Tail Lights
184,000mi
Body:
8" Fabtech Lift
37" Toyo Open Country M/T
18" Rockstars
15" Cieling DVD
Engine:
99.5+ Conversion
AFE Stage 2 Intake
4" Turbo Back Exhaust
Ceramic Coated Bellowed Up-Pipes, Exhaust Manifolds, High Flow Turbo Outlet
ITP In-Tank/PRE-Pre-Pump Mod
HP Oil X-Over Line
AIH Delete
ISSPRO Boost, Pyrometer, Trans Temp A Pillar Gauges
CCV Mod
Truspeed

Other Rides:
67' Camaro RS/SS Dart Big M 540cu
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post #2 of 2 (permalink) Old 08-11-2008, 04:01 PM
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Probably the best way to keep it from trying to fire is to pull the IDM power relay. With the valve covers off, you probably have the 42 pin connector over the driver's side disconnected. That will do the trick too.

I tested my compression at around 75k and all cyls were right around 400. A friends tested in the mid-high 400's, (don't know his mileage at the time). AFAIK, there's no initial compression specification. The book says that if the lowest cylinder is within 75% of the highest, the engine's OK. If they're all way down, you'll be seeing other evidence of that, such as hard starting.

You should crank with the starter for the same number of "hits" on each cylinder for the best comparison.

Hope that helps.

First truck -- 1929 Model A Ford pickup, restored from ground up. Wish I still had it!
99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

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  Diesel Forum - TheDieselStop.com > 1999-2007 Ford Super Duties > '99 & up 7.3L Power Stroke Engine and Drivetrain

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