LB7 Duramax injection test tooling

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03-07-2017, 17:06
LBritton

LB7 Duramax injection test tooling

I have a 2003 GMC HD 2500 and a work truck, service body 2004 Chevy HD2500 with Duramax LB7s in them. Not sure of the actual miles on the 2004 but having a start issue after it sits for over 1 minute. We have changed the fuel filter base and hoses eliminating an air in fuel issue. The issue is the same on a hot or cold engine. We are suspecting leaking injectors or a bad lift pump. If you let the glow plugs cool and hit it with ether and get some RPMs it will go on and run fine. Very smooth no smoke and plenty of power. Shut it down and restart within 30 seconds pretty normal. Shut down 45 seconds and crank it will restart but more cranking. Let it sit over 1 minute and it cranks fine and fast but will not start or even hit and no exhaust smoke. There is a test in the manual for vacuum to check the mechanical lift pump lines etc. Then a pressure gauge to check high side pressure up to 28,000 PSI.

Is there a tool group available to check these 2 functions on the LB7 engines?
03-07-2017, 18:54
DmaxMaverick

Your trucks don't have lift pumps, unless you or someone installed them. The fuel system is suction from the tank to the pump in the engine valley. It sounds like you have air leaking into the system, somewhere. A leak that allows air into the system will also allow the fuel to drain back to the tank when off. A large leak should set code(s), likely P0093/P0193. Is the SES lamp on?

Fuel pressure can be monitored and tested with an OBD II scanner (Tech II, etc.). The tools needed are already built in. The fuel supply system vacuum can be monitored with a gage installed at the test port at the front/right of the engine (brass fitting). Kennedy Diesel sells a gage that plugs into that.

Ultimately, you'll probably find that it's time for a set of injectors.

The use of ether probably killed all your glow plugs.
03-08-2017, 13:37
Kennedy

Quote:

Originally Posted by LBritton

I have a 2003 GMC HD 2500 and a work truck, service body 2004 Chevy HD2500 with Duramax LB7s in them. Not sure of the actual miles on the 2004 but having a start issue after it sits for over 1 minute. We have changed the fuel filter base and hoses eliminating an air in fuel issue. The issue is the same on a hot or cold engine. We are suspecting leaking injectors or a bad lift pump. If you let the glow plugs cool and hit it with ether and get some RPMs it will go on and run fine. Very smooth no smoke and plenty of power. Shut it down and restart within 30 seconds pretty normal. Shut down 45 seconds and crank it will restart but more cranking. Let it sit over 1 minute and it cranks fine and fast but will not start or even hit and no exhaust smoke. There is a test in the manual for vacuum to check the mechanical lift pump lines etc. Then a pressure gauge to check high side pressure up to 28,000 PSI.

Is there a tool group available to check these 2 functions on the LB7 engines?

What you describe is typical of the 2003-2004 era injectors. I've seen trucks that started cold but not warm. I've seen them that did not start ever without ether etc. Quite common and several variations. The injector return flows are excessive. I would not bother testing I would replace the injectors. The shot of ether gets you just enough pump speed to produce enough flow that the proper minimum starting pressure can be achieved. The injector return flows are excessive. Drop me a line and we'll get you set up with the right stuff including lift pump.