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LBZ issues -- Help Needed - please

K

Kennebago

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Location
Maine
I will try to keep this short but can supply more info if it will help. Recently bought a 2006 GMC crew cab with the LBZ engine. In short, I have some problems. The truck has about 120K miles and body is in good shape. I should have looked closer to start but...here I am. The truck starts and runs great for a few minutes but as soon as it is warmed up it loses power. Shut off, wait a while and everything repeats. It has after market lift pump (FASS) and it is obvious it has been messed with a bit (big stacks, looks like injector pump may have been replaced) etc. Replaced fuel filter / separator, no help. Checked the fuel lines and replaced all fuel lines with OEM lines - some lines were pretty bad, collapsed inside -- no help, replaced fuel pressure sensor, no help.
There have been some codes tossed along the way - low fuel rail pressure for one, some fuses blown on FASS circuit (bad electrical connections), fuel leaks ( in vicinity of pressure sensor) now fixed .....but still start it, run for a while and what I assume is limp mode.
I don't want to just keep replacing stuff as now the obvious things are done and the cost of components gets higher. I would really appreciate your help. If you can tell me what info will help you help me I will try to get it.
The fellow actually working on the truck is an excellent auto mech friend of mine. Great mechanic but NOT a diesel mechanic so he is good and he is meticulous...but does not have the knowledge that is present in this group.
Your inputs will be much appreciated .... and ... I can take the truth.

By the way, any good diesel shops in the MA, NH, Maine area - just in case it gets to that

Thanks
Jerry
 
The stock fuel filter is still in use? The one on the pass side of the engine. The prime pump on that can have bad seals. If you replaced fuel hoses, did you do all of them under the hood? What exactly are the codes? Limp mode from the factory (if memory serves-been a while) is 2nd gear and around 2000 RPM. I'd be inclined to try running it without the lift pump (bypassed).
Do you know what tune is on the truck?
For starters...
 
You are collapsing fuel lines. :wtf: The only thing I know that will suck a fuel line flat is a restriction. Depending on where the lines were flat I would suggest dropping the tank and looking for restrictions in the fuel pickup assembly. Diesel will vaporize under a vacuum and vapor lock things. Air leaks also stop the engine. Any restrictions in the fuel system will make air leaks worse.

The FASS must be running for fuel to move. If it stops running so does your engine from fuel starvation. Check that the motor is running when the engine stalls as the FASS may be failing or have bad power/ground issues still.

Does the FASS have any fuel heaters or is it gelling/waxing the unheated filters?
 
WarWagon said:
You are collapsing fuel lines. :wtf: The only thing I know that will suck a fuel line flat is a restriction. Depending on where the lines were flat I would suggest dropping the tank and looking for restrictions in the fuel pickup assembly. Diesel will vaporize under a vacuum and vapor lock things. Air leaks also stop the engine. Any restrictions in the fuel system will make air leaks worse.

The FASS must be running for fuel to move. If it stops running so does your engine from fuel starvation. Check that the motor is running when the engine stalls as the FASS may be failing or have bad power/ground issues still.

Does the FASS have any fuel heaters or is it gelling/waxing the unheated filters?
Click to expand...
These trucks are NOTORIOUS for collapsing fuel lines. GM used a rather cheap nylon line with not much resistance to collapsing in a system under vacuum. And some FASS pumps are flow on fail, so not all of them must be running for the engine to run. We need to know what codes(s) it is throwing 1st. My guess is your getting a P0087 which is rather common for LBZ's. Next you need to get a vacuum/pressure gauge on the fuel test port located on the upper passenger side of the engine by the alternator and see if it is holding pressure from the FASS or if it is holding a vacuum. Check the basics BEFORE you throw parts at it.
 
If you hammer an LBZ from stop or low speed and it's below 20 degrees outside you can almost COUNT on a code P0087. Same thing in any temperature any time there is about 1/2 of the fuel filter used up. I would still be suspecting fuel lines under the hood (1st to weaken due to heat) and the lift pump. Check at the test port as Ferman said.
 
Thanks guys for the inputs - let me get at this and see what more info I can provide. I appreciate your help. It may take me a bit of time to take the next steps but I will post the requested info as I get it. Thanks

Jerry
 
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