Ok saw this --> Chevrolet-GMC Diesel Diagnostics

Gonna try clear Lines...

 

Remember that the fuel system from the fuel tank up to the CP3 or CP4 operates on vacuum, and air can leak into the system without fuel leaking out.

Leave the Schraeder valve alone for now, just pump the primer button until it gets hard, then loosen the bleeder screw a little. Once air has been bled up to this point pump again with the bleeder screw tightened. If you have pumped 30 times or more and the primer button is not hard, something is wrong.

Let us know

 

Check both of your fpr and temp sensors are in the correct places they won't set a code but and will slowly still build pressure but won't allow it to fire.
First fpr on the pump uses one black and one yellow wire
2nd fpr on the rail uses one yellow and one purple/white wire
fuel Temp sensor on the lower rear of the pump uses one brown/gray and one brown/white wire.
I've also had an lml I did injectors on before that were brand new 100% s&s and they lost prime somehow. I put 80 or 100 psi of air in the return line and it fired up. Happened to another member here years ago too. Had an lml they did injectors on and the shop couldn't get it to fire and that's what it ended up being. Doesn't happen often. Check your regulators and temp sensor are in correct place if they are try the air trick and report back.

 

I went through and checked all the connections, all are there... I'm still not getting a reliable low-pressure prime.. its always just full of air, so It's still sucking air somewhere...

I've replaced the input and output lines to the filter. The seals on the prime pump on the filter housing... but I've ordered a complete set of low-pressure lines...

This is the only line without a home...

It's amazing how many "lost" connections show up...

 

I went through and checked all the connections, all are there... I'm still not getting a reliable low-pressure prime.. its always just full of air, so It's still sucking air somewhere...

I've replaced the input and output lines to the filter. The seals on the prime pump on the filter housing... but I've ordered a complete set of low-pressure lines...

This is the only line without a home...

View attachment 1120040

It's amazing how many "lost" connections show up...

That goes to the vgt sensor on turbo.

 

That look like it should go to the turbo from what I remember?

 

That does look like it goes to the turbo but I can't remember for sure or what it's for

 

Should go to the vane control solenoid on the turbo, but that shouldn’t keep it from running I don’t believe. Have you pinched off the return line to get it to build up pressure on the return?

 

Should go to the vane control solenoid on the turbo

I'm pretty sure you're right. Him having pulled so far out was throwing me off.

 

Pinch the return from the engine

 

In disassembly i found the fuel connection to the passenger fuel rail loose. Tightened, primed and i got a quick start then it died, gonna re-prime and go again but the batteries are pretty weak, charging em up...

I am able to get a "hard" prime on the pump now though...

 

Still no start, no codes...

Pinch the return from the engine

Where exactly should I pinch the line? Right where it goes into the driver side fuel rail?

How long do I leave it pinched off?

Edit: I have an Autel 808 anything I can look at on it to assist?

 

There are 2 fuel lines that come into the engine bay near the master cylinder from underneath the truck. There is a metal quick connect on both lines, the smaller line is the return. Pinch the return line on the engine side of the quick connect. You need 55 PSI pressure to get the engine to start.

 

Ok I pinched the small one off and no joy... I'm able to get the primer to be hard before cranking, no air, solid stream from bleeder...

I've ordered a set low pressure side fuel hoses, I'll replace those, though I have replaced a couple so far already just because...

What "Live" data point can I look at on the service computer to give a hint of the issue?

These are the pressure numbers I'm seeing now (autel mp808s)...

Desired fuel rail pressure (FRP) 5849 psi
Fuel rail pressure sensor (FRP) 65 psi
Fuel rail reassure sensor (FRP) .49v

 

How long do I leave it pinched off?

Until it starts. Note that once fuel is drained from the fuel rails, it may take several (4-5, maybe more) instances of cranking the engine for 15 seconds at a time, to produce the necessary rail pressure. Don't overheat your starter!!

With that information, you know that your ECM is demanding enough pressure to start, and that fuel pressure is not being produced.

Get a subscription to ALLDATADIY.COM (or another similar) for your truck, short term or long term, your choice.

Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis
Chevrolet-GMC Diesel Diagnostics
Chevrolet TSBs (Technical Service Bulletins)
TechLink
https://www.acdelco.com/techline-connect-information-system

 

Until it starts. Note that once fuel is drained from the fuel rails, it may take several (4-5, maybe more) instances of cranking the engine for 15 seconds at a time, to produce the necessary rail pressure. Don't overheat your starter!!

OK understood... I didn't crank it near enough with it pinched

With that information, you know that your ECM is demanding enough pressure to start, and that fuel pressure is not being produced.

ahh i see, makes perfect sense

Get a subscription to ALLDATADIY.COM (or another similar) for your truck, short term or long term, your choice.

That's a great resource!! I borrowed a factory service manual yesterday, but I'll have to give them back (eventually)

Thanks I'll report back..

 

Update: I bought a vacuum/ pressure guage to put on the test port and it's sucking air somewhere.. I had to walk away though as I have to go on the road for a bit for work...

 

yea that was a long work session... 2 years later im working on the truck again... same issues.. never resolved... Its been in the garage the entire time, haunting me, taunting... calling "hey looser... what about me?"

An now I need the space.. so here we are again...

ill ask for a technical dispensation on the resurrection of old threads rule, but I figure this is the exact same problem, that was never resolved, the historical info is important.


I spent yesterday getting to the truck and getting the electrical, batteries etc back to par... then today going back through it..

The fuel pressure gauge on the shraeder value won't hold a pressure value long at all, I can prime it up with the manual primer on the filter housing, and open the bleeder screw till I get a steady stream, pump it up, but it bleeds down to 0 over a couple minutes.

I replaced low pressure rubber hoses, and clamps to make sure no air was getting sucked in and I can slow the leak down, but it never holds pressure.

is that indicative of a low pressure side leak? seems so

thoughts?

 

Did you ever figure out the cause of this no start? I'm in this boat now. About to just trailer it to the shop.

 

Yes I figured it out, had two issues one was a bad rebuilt injector, other was air in return line, had to pinch off return line and it fired up. Which lead me to find the bad injector.

 

There is a check ball that may be stuck open in the top center of the unit. Get a rebuild kit for your fuel filter holder/base, or buy a new part.

 

I checked this and double check the primer pump rebuild. Still trying to prime it.. this has been going on way too long..

The PBD computer never shows more that 102 for the fuel rail sensor. Im really at a loss here... im planning on having a friend c9me over and pump the fuel primer.. Crack the screw let any air out (if any) then crank for 5 seconds and repeat until it starts.

Any other strategies?

-- Chris

 

See the attachment