2003 6.0 low relative compression #7

[kevin41]

Have another good 6.0 story, I have a customer with an early build 6.0 with 187,000 miles. F250 was towed in last week with no high oil pressure.High pressure oil pump was bad, replaced high pressure pump and truck ran great. Finished the work last saturday drove the truck home, took my family to church on sunday, drove it in on monday and returned it to the customer.Towed it back in tuesday miss on #7, relative compression #3 and #7 low, power balance #7 dead. Customer told us prior to high pressure oil problem he replaced #3 and #7 injectors all injector electrical tests passed. Pulled v.c. and high pressure rail removed injectors everything was installed correctly.Inspected rockers and push rods looked at valve springs all seems o.k.Swapped injectors to retest #7 drops out. Will do manual compression test in the morning, seems weird that the injectors the customer replaced developed compression issues in the same cylinders. If anybody has any insight to what the problem might be or what to test next it would be greatly appreciated. Thanks for taking the time to read my story.

[Keith Browning]

Sounds like a pre-existing cylinder problem possibly caused by the original injectors but that does not explain why it ran "okay" for you after replacing the HPOP. Perhaps when you get to a precise diagnosis we can come to a conclusion. Sorry that this offers no suggestions.

[lmorris]

Have a real good look at the injector tip on #7. I bet it has a crack in it. If so it may have buggered the piston. Have a look at the glowplug as well, it may be damaged.

[ETS]

You guys have any ideas why it seems #7 always is the one with problems?

 

The last 4 trucks with cylinder issues I have seen here all had #7 weak or dead. 2 trucks had other cylinders also. My personal truck [2006 F350] had cracked head at #7 injector cup.

[kevin41]

Ran manual compression test this morning, #7 50 psi. Customer authorized removal of cylinder head and the top of the #7 piston is destroyed, I Can only guess that the old injector nozzle broke and pieces were left in the cylinder, and the customer did not realize it when he changed the injector. I will try and post pictures tomorrow but it is nothing we have not all seen. Thanks for the help.

[cbriggs]

#7 is the first injector to get starved for fuel in a low fuel pressure situation. Low pressure / no fuel will crack the injector tip. I think all trucks I have ever seen crack an injector tip could be traced back to a fairly recent fuel starvation issue. Mostly plugged filters or bad pumps, but one guy actually admitted to running his truck out of fuel a few months prior.