Fuel Leak

Corey Owner/Technician Kenton, Ohio Posted   Latest  
Discussion
Driveability
Other
2002 GMC Sierra 3500 6.6L (1 LB7) 5-spd (NV4500/MW3)—1GDJC341X2E153616
Poor Fuel Economy

Anyone have one of these GMC 6.6L that filled the crankcase up with fuel in one week and have no visible signs of fuel leaking? I've pulled the valve covers and ran it and saw nothing. Tried letting it run for over an hour to heat up and also put dye in it but still no signs of a leak anywhere. Engine is clean as can be on the inside because customer has been changing oil every week with over half of it being fuel. He had the injectors replaced about a year ago by another shop and had this same problem and it was a fuel line but I'm not finding any leak this time. It starts up great with no problems and runs fine with plenty of power and also doesn't smoke. Would seem to be it has to be on the fuel return side than but nothing seems to be wrong looking over it with the UV light.

0
Randy Curriculum Developer
Raleigh, North Carolina
Randy Default
 

Have you checked the drive side of the high pressure fuel pump ? That type of leak might be minimal at idle but increase with fuel rail pressure.

+1 Default Ð Bounty Awarded
John Technical Support Specialist
Commack, New York
John Default
 

I have seen the pump leak from the shaft seal behind the gear into the engine a few times.

0 Default Ð Bounty Awarded
Scott Owner
Moreno Valley, California
Scott Default
 

Corey, If the return lines/seals have been ruled out, what are the balance rates on the injectors? My first thought would be a injector(s).

0 Default Ð Bounty Awarded
Scott Owner
Moreno Valley, California
Scott Default
 

Another thought I had would be to command the CP3 pump to maximum pressure (I think it's 155 MPa) and recheck it again - if the valve covers are still off. Does the CP3 pump get to that pressure? I personally haven't had a HPP leak internally, but I guess it could happen. You might possibly see this through the oil fill tube. When I do these I always put new seals on and replace a lot of bolts…

0 Default Ð Bounty Awarded
Nathaniel Diagnostician
Ashton, Ontario
Nathaniel Default
   

It would be good to know that the injector balance rates were in range, but with new injectors and zero driveability concerns, the guys are probably right: CP3 leaking internally. I know of no solid way to test for this, but you can do a compressed air leak-down test at the high pressure outlet back into the pump to test the three high pressure check valves. Any leak-down would indicate a…

0 Default Ð Bounty Awarded
Corey Owner/Technician
Kenton, Ohio
Corey Default
 

Balance rates are 0.00 with CMD being 0.37. The pump will go up to 160 with the scan tool and the actual holds right to it.

0 Default Ð Bounty Awarded
Scott Owner
Moreno Valley, California
Scott Default
 

Hi Corey, Doesn't that seem unusual to you that all balance rates are 0? Is this with the truck moving, or at an idle? I've put a few sets of LB7 injectors on and I've never seen balance rates that are all 0 mm3. What are you using for a scan tool? I've also never seen all injector commands being identical either, as this will move depending on whether the individual cylinder is too rich/too…

0 Default Ð Bounty Awarded
Corey Owner/Technician
Kenton, Ohio
Corey Default
 

Hi Scott, Yes I thought that the balance all being zero was unusual also. But I posted what the SnapOn Solus Edge said it was. the command did very just a slight 0.37 and 0.36 but it was idling and all 0. Yes I still have the valve covers off and checked the lines and injectors while commanding maximum pressure I didn't see any leak and I cann't see down the fill tube very well with it bending…

0 Default Ð Bounty Awarded
Scott Owner
Moreno Valley, California
Scott Default
 

Hi Corey, I think Snap-on has an issue with those PID's. Can you borrow a Tech 2, or try another scan tool? It's impossible for balance rates to all be 0. I'm not saying this is the issue and I hate wasting your time, but the process of testing and analysis is comprised of tests - not just to find what is wrong, but also to see what is right. Given what's out there for LB7 injectors, especially…

0 Default Ð Bounty Awarded
Troy Owner/Technician
Longbranch, Washington
Troy Default
 

I am thinking that much fuel it would be noticable in a cylinder so it would almost have to be the pump, can you see the front of the pump like a cover or something that can be removed to see if its leaking

0 Default Ð Bounty Awarded
Victor Owner/Technician
Doral, Florida
Victor Default
 

Check for cracked injector bodies.

0 Default Ð Bounty Awarded
Maynard Technician
Elmira, Ontario
Maynard Default
 

Scott Chase has you steered in the right direction I think. We had a truck of the same years as yours I believe... maybe it was 2003. Client had injectors done in the not so distant past and was now coming in with crankcase way overfilled, (a couple of times) so we decided to do the long version of testing, valve covers off and run the truck, no leaks, but when pressure was commanded higher and…

0 Default Ð Bounty Awarded
Dan Owner/Technician
Canton, Mississippi
Dan Default
 

You may want to check to make sure the gas cap is venting. I've seen issues just like this when the gas cap didn't vent. The pressure build-up in the gas tank would create enough pressure to push the fuel through the injectors even when not activated.

0 Default Ð Bounty Awarded
Corey Owner/Technician
Kenton, Ohio
Corey Default
 

Seriously? A diesel letting fuel through the injectors because of fuel tank pressure? These things are for 1000 + psi running. I would think the nylon lines would blow or have a leak else where before the pressure would push through the injector.

0 Default Ð Bounty Awarded
Dan Owner/Technician
Canton, Mississippi
Dan Default
 

Sorry, didn't see that it was a diesel. My mistake. :-O

0 Default Ð Bounty Awarded