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Discussion Starter · #1 ·
I was working on my truck and al completely stumped at what’s happening. I have a 2003 lb7 with fass lift pump and it would crank but not start. the lift pump was on. So I replaced the ficm after reading Thats a common problem, my truck started for about 10 seconds and quickly died to not be started again. Not a single fuse is blown and I am getting diesel to the injectors. Does anybody know what could be going on
 

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Discussion Starter · #2 ·
I was working on my truck and al completely stumped at what’s happening. I have a 2003 lb7 with fass lift pump and it would crank but not start. the lift pump was on. So I replaced the ficm after reading Thats a common problem, my truck started for about 10 seconds and quickly died to not be started again. Not a single fuse is blown and I am getting diesel to the injectors. Does anybody know what could be going on.
Wiring looks okay, fuses are good, diesel is there, battery is charged
 

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Welcome to DieselPlace
Any codes?
Start inspecting your fuel lines from filter head to CP3. Look for any kinks, dry rot, cracked lines etc. Replace any that are in questionable shape.
Inspect your engine harness for any rubbed through wire insulation, broken wire, corrosion, loose connections, etc
 

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Discussion Starter · #4 ·
Welcome to DieselPlace
Any codes?
Start inspecting your fuel lines from filter head to CP3. Look for any kinks, dry rot, cracked lines etc. Replace any that are in questionable shape.
Inspect your engine harness for any rubbed through wire insulation, broken wire, corrosion, loose connections, etc
Some codes that came up included u1800, p0090, p0193,p0380, p0540. But after I cleared them and attempted to start it again they don’t come back. Ive been inspecting everything I can and it still just doesn’t seem to want to fire even After I installed the FICM it ran for about 10 seconds and died. And don’t see any signs of electrical or rubbed wire problems. Thank you again for the response, I will look over all my lines and wires once again, Im so lost truthfully anything helps
 

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Discussion Starter · #5 ·
Some codes that came up included u1800, p0090, p0193,p0380, p0540. But after I cleared them and attempted to start it again they don’t come back. Ive been inspecting everything I can and it still just doesn’t seem to want to fire even After I installed the FICM it ran for about 10 seconds and died. And don’t see any signs of electrical or rubbed wire problems. Thank you again for the response, I will look over all my lines and wires once again, Im so lost truthfully anything helps
Would a kinked rubber fuel line cause it to not start?
 

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Discussion Starter · #7 ·
Yes, a kink in a fuel line = a fuel restriction.
Went to Napa and got replacements for any fuel lines that looked in rough shape and still have the same problem. I see many lb7 users have problems with the oem fuel filter housing but mine had been bypassed for a fass system. And I know I’m getting fuel to the injectors. Maybe just not enough or even to much but it’s such a pain to figure out. From forums I’ve read it really seems like it’s narrowed down to the cp3 and/ or injectors because even my FPR is in good shape. I just wish there was a way to know before I just start throwing parts at it
 

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Went to Napa and got replacements for any fuel lines that looked in rough shape and still have the same problem. I see many lb7 users have problems with the oem fuel filter housing but mine had been bypassed for a fass system. And I know I’m getting fuel to the injectors. Maybe just not enough or even to much but it’s such a pain to figure out. From forums I’ve read it really seems like it’s narrowed down to the cp3 and/ or injectors because even my FPR is in good shape. I just wish there was a way to know before I just start throwing parts at it
You need to see what the actual vs desired fuel pressures are.
 

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Discussion Starter · #9 ·
You need to see what the actual vs desired fuel pressures are.
What would the best way around that be? Someone with a pro scanner to see what’s going on? I don’t think my edge monitor shows that information
 

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I know that while cranking my gauge does show about 6.5 k psi
That should be about right for starting and idle
Any good scanner should read live data to some degree.. Most auto parts stores have one they use to read vehicles in the parking lot or rent to customers.

I would also start shaking the engine harness in various areas while some one is cranking the engine over to see of things improve ..

My thinking is a fuse is not making a connection, burned, or electrical connection issue somewhere
 

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Discussion Starter · #12 ·
That should be about right for starting and idle
Any good scanner should read live data to some degree.. Most auto parts stores have one they use to read vehicles in the parking lot or rent to customers.

I would also start shaking the engine harness in various areas while some one is cranking the engine over to see of things improve ..

My thinking is a fuse is not making a connection, burned, or electrical connection issue somewhere
Jeez really leaves me with a lot of things to go wrong then, I did inspect the middle harness that goes across the center on the engine but didn’t see and dings or anything. If it still cranks but just doesn’t fire it could still be an electrical issue. Sorry for all the questions
 

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Jeez really leaves me with a lot of things to go wrong then, I did inspect the middle harness that goes across the center on the engine but didn’t see and dings or anything. If it still cranks but just doesn’t fire it could still be an electrical issue. Sorry for all the questions
There have been a few cases of the contacts in the fuse box have been spread too far apart and do not make a connection with the fuse..
Burnt fuses have been missed before
A short to ground can create a no-start condition.

The Duramax is known for wire harness issues
 

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Discussion Starter · #14 ·
There have been a few cases of the contacts in the fuse box have been spread too far apart and do not make a connection with the fuse..
Burnt fuses have been missed before
A short to ground can create a no-start condition.

The Duramax is known for wire harness issues
Then being bad for that has been a lot of what these forums around about but it’s crazy that it was fine everyday up until one morning it just didn’t want to go. If it is would it be worth replacing the entire harness?
 

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Then being bad for that has been a lot of what these forums around about but it’s crazy that it was fine everyday up until one morning it just didn’t want to go. If it is would it be worth replacing the entire harness?
Only if you find issues. No sense replacing something that is not needed.
Take your time and search well. rushing things leads to making mistakes

Electrical issues can be a big pain in the rear..
 

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Discussion Starter · #16 ·
Only if you find issues. No sense replacing something that is not needed.
Take your time and search well. rushing things leads to making mistakes

Electrical issues can be a big pain in the rear..
I guarantee it, And the newer you go the more there is. I just can’t seem to see anything wrong with anything that’s why I’m so lost. But obviously something is definitely wrong. To inspect how would you start?
 

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I guarantee it, And the newer you go the more there is. I just can’t seem to see anything wrong with anything that’s why I’m so lost. But obviously something is definitely wrong. To inspect how would you start?
I would start at the fuse panel under the hood and inspect wires out from there.
Inspect around the alternator and FICM really well. The FICM harness and connector are also known to have issues
 

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Discussion Starter · #18 ·
I would start at the fuse panel under the hood and inspect wires out from there.
Inspect around the alternator and FICM really well. The FICM harness and connector are also known to have issues
I think it has a lot to do with it being previously washed down under the hood. And now the injectors or cp3 just aren’t getting the voltage they need from somewhere. I’ve inspected every wire and fuse I can and nothing seems out of the ordinary. I’ve read that maybe wd-40 may help those connections out
 

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I think it has a lot to do with it being previously washed down under the hood. And now the injectors or cp3 just aren’t getting the voltage they need from somewhere. I’ve inspected every wire and fuse I can and nothing seems out of the ordinary. I’ve read that maybe wd-40 may help those connections out
WD40 is a water displacement product.
If you washed down the engine then I would start disconnecting each of the harness connections, blow it out with some compressed air and use some electrical contact cleaner
 

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Discussion Starter · #20 ·
WD40 is a water displacement product.
If you washed down the engine then I would start disconnecting each of the harness connections, blow it out with some compressed air and use some electrical contact cleaner
I’ve already done that all and seems to have no luck what do ever. Replaced ficm, wiring looks okay, can’t find any corrosion or any bad things with fuses or connector pins. I’m out of ideas at this point almost makes no sense. Almost convinced to just replace the ecm at this point but like I said I don’t want to just keep throwing money at it
 
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