Fuel leak - Page 4 - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

LinkBack Thread Tools Display Modes
post #31 of 34 (permalink) Old 08-08-2017, 12:29 PM
Senior Member
t.ashton's Avatar
Join Date: Jan 2011
Location: Red Oak, TX
Posts: 669
Blow by is compression gasses entering the crank case, so probable causes are cracked piston, bad rings, scored piston walls, any way the gasses can find there way out of the cylinder besides going out the exhaust stroke. Blow by usually indicates a substantial problem.

2004 Silverado Cali lb7, Airdog ll 165, fresh sticks at 325k, Rick Fletes Dsp 5 on v2, 33x12.5 nitto at on 20 inch American Racing 20x10 wheels, Stage 5 Built Transmission by Mike Cole with triple disc billet low stall converter, 4 inch Injen cold air intake, Profab Intake Horn, Batmo Wheel, PPE Race Valve, Full EGR Removed w/ fed belt, 3.5 inch MBRP Downpipe, Full five inch MBRP Exhaust axle dump, lbz cp3 pump, Dual Yellow Top Optimas, High Output Alternator, Cognito Pittman and idler w/ support kit, Cognito Upper Contol arms, Drilled and Slotted Rotors on all four Corners, FED Y Bridge, Shantz Custom Fab Traction Bars.
t.ashton is offline  
Sponsored Links
post #32 of 34 (permalink) Old 08-08-2017, 01:22 PM
DuramaxForum n00b
RdHammer's Avatar
Join Date: Aug 2013
Location: Homer IL
Posts: 22
Originally Posted by peyton4x4 View Post
Could a bad copper seal cause the blowby, or maybe a lifted cup causing the blowby? I'm thinking I may have a loose seal on the return line with a lifted cup or something wrong in the cup causing the blow by. Is there a way without a techll I can cut off one cylinder at a time?
Improperly seated cups or worn/damaged cup seals would cause blow by and I imagine the copper seal if damaged would also. You could disconnect the injectors set by set maybe and see if that would narrow down the pool. They are in pairs, and you should have 4 connectors off the harness for the injectors.

Sent from my SM-G930V using Tapatalk

01 Sierra 3500 LB7 Dually - MBRP 4" Duals...more to come soon!
RdHammer is offline  
post #33 of 34 (permalink) Old 08-08-2017, 08:57 PM Thread Starter
Junior Member
Join Date: Mar 2017
Posts: 50
I understand that bad rings, etc can cause blow by I've been in the mechanic business for a little while, but this is my first diesel. I know this is a lot different than the old sbc, but worn rings is something that happens over time, not out of blue one day great then next bam no compression out of nowhere. I'm really leaning towards a lifted cup/bad copper seal, I won't know for a week though. Thanks for all the help guys.
peyton4x4 is offline  
Sponsored Links
post #34 of 34 (permalink) Old 08-18-2017, 05:26 PM Thread Starter
Junior Member
Join Date: Mar 2017
Posts: 50
Problem ended up being a bad oring on my number 6 injector and bad return line seal. All is well now.
peyton4x4 is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Chevy and GMC Duramax Diesel Forum 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:


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