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.

LinkBack Thread Tools Display Modes
post #1 of 2 (permalink) Old 08-11-2008, 01:21 AM Thread Starter
Senior Member
Bacon104's Avatar
Join Date: Apr 2007
Location: Nor Cal
Posts: 241
My Photos: (18)
Feedback Score: 0 reviews
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?

Early 99 F-350 (99.5+Conversion)
Lariat Crew Cab Long Bed
05'-07' Front End/08' Tail Lights
8" Fabtech Lift
37" Toyo Open Country M/T
18" Rockstars
15" Cieling DVD
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

Other Rides:
67' Camaro RS/SS Dart Big M 540cu
Bacon104 is offline  
Sponsored Links
post #2 of 2 (permalink) Old 08-11-2008, 04:01 PM
Lifetime Supporting Member
klhansen's Avatar
Join Date: Jan 2003
Location: Eagle River, Alaska
Posts: 22,639
My Photos: (180)
Feedback Score: 0 reviews
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.

Hard or no-start? Check Here
klhansen is offline  
Sponsored Links

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

Quick Reply

Register Now

In order to be able to post messages on the Diesel Forum - TheDieselStop.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome