Alright had a 03 lb7 dually brought to my house for loss of power/limp mode and white smoke out of exhaust. He took it to other shops and they couldn't figure it out so i got stuck with it. After initial inspection i noticed the fuel feed and return lines were wet with fuel (thought great i just found the problem). Tripped a code p0087 and p1093. I hooked my gauge to the fuel service port and it reads 20 inches of vacuum at idle!!!! so obviously there is a major fuel restriction in the system. Not sure if its filter or tank pick up yet. Here is my question... should i address that high fuel vacuum first or look into other things also? I pulled up actual FRP and desired FRP and graphed them while brake torquing. The actual will keep up for a bit then fall off then spike high when i let off the throttle.... assuming because of lack of load when i let off throttle. I commanded fuel rail pressure to max and it holds at idle. So does this tell me the injection pump is good? i would think so but i havnt dug into these a whole lot on systems with no lift pump. so what are your initial instincts guys? is the fuel restriction definitely the starting point? or can anything else cause the high fuel vacuum?? ill post a video of the FRP graphing from scan tool.
need opinions on lb7 diagnostics
- Thread starter C.bowles2
- Start date
Does it have a plastic fuel filter on it? I've seen the high vacuum with them because the detent to release the check ball was missing, and so it wouldn't release the check ball. That, and it could also be double sealed. The inner seal of the filter can stick to the center portion. It will let the filter thread on far enough to seal, but not to push in the check ball.
When i get some free time im gonna run a straight line from the fuel feed quick disconnect to a jug of diesel and see if my vacuum still reads the same, if so ill replace the fuel filter then see what happens i suppose. Just wanted to touch base with some of you on this to see if im missing something. Im not that familiar with lb7's. Also was gonna ask if there is a fuel pressure release valve on lb7's??
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