LLY Losing Fuel Pressure

[millerman04]

A friends LLY is losing fuel pressure. He just recently changed the fuel filter thinking that was the problem. But it didnt fix the issue. He said his rail pressure is around 17,000. Not sure if that was at wide open throttle or nt. He didnt give me much details, just that it doesnt have the pressure it should. What could be the problem or problems? Thanks guys!!

 

[blk smoke lb7]

Gonna have to find out what his commanded and suppyed are.Does he have a v2 to do a log? Could injectors relieving to easy cp3 getting week

 

[DBUSHLB7]

Might need a plug in the rail?

 

[millerman04]

I dont think he has a V2. I do though. He has EFI on his truck, but im not sure if he has the V2 with it. He said he's runnin the better than stock tune on it. What plug in the rail was you referring to? I thought maybe a fuel regulator was acting up?

 

[dirttymaxx]

hes talking about the shimmed rail mod

 

[millerman04]

Oh ok. Wasnt sure. He's saying it changes tone out the exhaust almost like the timing changes at idle. He's emailed SoCal diesel with his problems. They told him that hes losing rail pressure. Its only carrying 9500 psi. That was at WOT

 

[dirttymaxx]

if hes losing rail at WOT my guess would be the cp3. but i woudl start out with cheaper thing like fuel filter,and if its a high miles truck,check the feed line to the cp3 from the filter head,i have seen them suck closed before.

 

[millerman04]

He changed the filter first thinking that was the culprit. But it wasnt. I'll tell him to check that line then. Thanks!!!

 

[Burn Down]

Need to make sure you have a good steady supply of fuel to the CP3. Lift pump working?
Need to do a bottle test.
Need to check injector balance rates.
Need to use a V2, Tech2, or just unplug the FPR, and recheck rail pressure. It should go to 24,000 psi + depending on tuning...
Need to check injector return rates. Injectors can have perfect balance rates & be returning to much fuel back to tank.
CP3 should be last on this list because it is the hardest to change...

 

[millerman04]

Thanks!!! :thumb:

 

[DBUSHLB7]

Is he getting low rail pressure codes? A close friend just went through this problem on his Kodiak (LLY equipped) heavy equipment service truck. After 3 truck repair shops couldn't figure it out we figured out that his fuel pressure relief at the back of the drivers side fuel rail was blowing open. A 50 dollar plug later and the thing is running like a champ! I realize a solid plug may not be the best option as it offers NO relief.

 

[Hot COCOAL]

The rail shim is easy sure and pretty cheap, but do you want to chase a problem? There is a thread about how to do a bottle test, here on DD. This test will, if done properly, conclude if a rail shim is needed. Find out, absolute, what IS your current problem, befor potentially compounding it. JMO.
Fuel pressure, fueling "issues" in general suck. Good luck.

 

[millerman04]

Just trying to help out a friend. Anything wiring, or fuel malfnction really does suck. Thats why i asked here. Ya'll been a great help!! :thumb:

 

[Hot COCOAL]

Does the owner experience the same issues in the stock tune? Does the owner run a lift pump? If the answers are no, then no, I would say the quick(temporary) solution would would be to add a lift pump, knowing a cp3 will be quick to follow(more than likely)IMO. Just a hunch, but I imagine the cp3 would struggle to keep up with just about any efi live tune, just cuz of age, milage, fuel quality etc. Adding an air dog or equivalent, will "feed" the cp3, rather than make the cp3 do all the work by drawing fuel up the draw straw all the way at the back of your truck in the fuel tank. By completely eliminating the work load, and supplying the cp3 you should be able to prolong its final gasp, for a little bit.

 

[millerman04]

Im thinkin his efi tune is a better than stock tune. A not so much more power tune of sorts. No lift pump on the truck. I mentioned to him that if the cp3 was getting weak, that adding a lift pump should help for now. I havent heard from him since yesterday. So im not sure whats hes tried yet.

 

[blk smoke lb7]

At this point with out a lift pump he could have killed the cp3 if he likes getting on it a lot.

 

[millerman04]

That i havent the slightest idea on. Not sure how he drives that truck.

 

[millerman04]

Went for a ride in that truck. On a cold start and a lower horse tune, it doesnt act up rite away. The warmer the engine gets, the easier it does it. With a bigger tune in, does it twice as fast. When he romps on the throttle it starts to build speed and r's but at around 2000 to 2500 rpm, then you feel the truck shutter, and wont build any more rpm's. What the shutter feels like is when a truck is about to go into limp mode, but his doesnt. So im not sure if maybe its a tranny issue, or a fuel issue. Maybe some of you guys have been through this before? Or maybe know what im talking about?