LLY: No start, low rail pressure.

[White Duramax]

Working on a 05 LLY c4500 41k on it. Truck started running rough while driving and will not start now. Rail pressure is around 700psi cranking, shows around 150psi key on not cranking. Filter has been changed, after cranking you can push the primer about 3 times and it is hard. I have done a bottle test, no fuel is getting by the fprv. Pulled all of the glow plugs and cranked, none of them blew fuel out. Ran each bank of injector returns into bottles, both about the same. Pump return put out more fuel than either bank of injector returns. No sure what to check next.

 

[bluecollar]

Will it start if u pump the primer while cranking. I had a pump returning fuel do this

 

[White Duramax]

Have not tried that yet, will have to get someone to crank it for me.

 

[chevyburnout1]

Sounds like you did all the correct tests. If all those results are correct then it sounds like an injection pump. However I would run all the tests one more time just to be safe.

 

[White Duramax]

Does anyone know the specs on injector and pump return while cranking?

 

[chevyburnout1]

4-5ml of fuel max per injector for 15 seconds of cranking. The injection pump does not have a specification for fuel returned.

 

[1953drtelco]

Subscribing

 

[bluecollar]

Mine i couild pump the primer with truck off and fuel would come out the return with out cranking.. new pump hardly any came out. Even with a lift pump i had to pump while cranking to start it.. it was a lower mileage lbz pump also

 

[White Duramax]

Tried pumping primer while cranking, still wont start. Bypassed tank and filter housing and tried to get it going out of a bucket of fuel, no good there either. Looking like the cp3 to me.

 

[bluecollar]

I bet so but i could watch mine pump fuel directly outta the cp3 return while pumping or lift pump on.. does the primer get hard and stay hard?.. just dont wanna point u towards the cp3 and not be it.

 

[White Duramax]

The primer will get hard.

 

[Stingpuller]

Check return on injectors

It sounds like the return is high on the injectors. I have had a few LLY's that wouldn't start (low fuel pressure) and the injectors was the fix. It should have 12ml per side cranking for 15 seconds. That's not much fuel!

 

[gmac32]

did you happen to check the relief valve on the back of the driver's rail? pull the horseshoe shaped hose off the rail and crank the motor over and see if any fuel is coming out of the relief

 

[White Duramax]

Checked the fprv-nothing coming out cranking. I may have to get something to better measure with and check return again.

 

[CrewCabMax]

Dealing with the same thing on an LB7. Good injectors and brand new FASS. 8 psi of fuel pressure, and crank no start. Hit it with a small squirt of ether(customer did it, not me) and it'll fire up and run like a champ. Just will not start on its own cold. Drive the truck for 30-40 mins and it'll crank long but will start. Let it set over night, and no start.

 

[durallymax]

Checked the fprv-nothing coming out cranking. I may have to get something to better measure with and check return again.

Get some graduated cylinders. As jeff said 12ml is the spec.

I dont have them for the LLYs but for LB7s it was 16ml per side but they allowed 20 depending on the fuels specific gravity.

There isnt a spec for the pump. Its the last part to turn to after every other test is run.

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[durallymax]

Dealing with the same thing on an LB7. Good injectors and brand new FASS. 8 psi of fuel pressure, and crank no start. Hit it with a small squirt of ether(customer did it, not me) and it'll fire up and run like a champ. Just will not start on its own cold. Drive the truck for 30-40 mins and it'll crank long but will start. Let it set over night, and no start.

Sounds like a loss of prime, air issue or high returns.

Good injectors means good balance rates? They can be good and still have high returns sometimes.

Can you log the rail pressure.

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[CrewCabMax]

The truck has no factory fuel filter, and is plumbed directly from the FASS pump, to FICM and then to CP3. With the FASS 8 psi of positive pressure, i would think that it would override any air in lines pretty quickly and start and run rough. When it does start, truck runs smooth, no weird idle as if there would be air in the system. I did the return fuel test on both banks and all came back within spec. Rail pressure is showing less than 500 on cranking and 178 with key on, engine off?? Haven not logged it driving yet to see if its keeping up with demand under pressure. Dont like ether starting.... LOL

 

[catman3126]

Sub.

 

[bluecollar]

Mine would run fine it would not hold rail on a big tune because all the return. My temp was also high.. when we bypassed the lift pump it would only run for 45sec i could watch the rail pressure drop and die. Filled a 32oz bottle pretty quick