LB7: 2003 LB7 Hard start when warm then stalling/no start

[nh_duramax]

I have a 2003 LB7. It has been starting hard when warm for a month now using the truck 2-3 times per week. Always started good cold (2-3 seconds). when warm could take up to 10 seconds maybe a little longer. Then this past weekend I replaced the fuel filter with an ac delco and had some trouble with the large o-ring but managed to get it to stay seated long enough to get the filter in place. Ran it for a test ride and got the same hard start after warm. Then today while at idle (on busy road) it stalled. Thought I was going to have to have it towed but after considerable cranking and about 20 minutes time it started. started driving home and it stalled again as I was going down the highway but I pumped the throttle a couple of times while rolling down the highway and it took off. Managed to make it all the way home (about 40 miles). shut it off when i got home and started it right back up. I started it again a couple of hours later and it idle for about 2 minutes and stalled. now about 6 hours later it still wont start. Also I get a low fuel rail pressure code p1093. While cranking the engine my scan tool shows a frp of 229 ( I am assuming the units are Bars) which is about 3300 psi. Any ideas, thoughts, etc... I have seen that some say only pump priming plunger three times or it will damage the filter head. Is this true for a 2003 LB7? It has 130Kmiles. I do not know if the injectors were ever replaced.

 

[Bryce418]

The extended crank warm points to a high pressure fuel issue, which is likely an injector return issue.

As for the primer question I'm inclined to call bs on that.

 

[adeso]

check the balance rates, check for fuel in the oil (drop a little bit on some paper towel and check for the fuel ring). Might also be a bad rubber hose that is collapsing when warm (but I would check the balance rates first) You can also do the return bottle test.

 

[nh_duramax]

Thank you for the responses. Would an injector return issue cause stalling at idle? I will look at the oil. I don't smell fuel in the oil, but that could just be a bad sniffer...I will try the bottle test.

 

[Bryce418]

No stalling from injector return issues just hard or no start.

 

[nh_duramax]

Thank you for the response. I know a guy in town that can run diagnostics on this, like the balance rates and I am going to pull the filter I put on and check the bleeder screw. Maybe I am loosing prime at idle or low rpm. Those were the only things I touched before the stalling started. Feels like I have multiple things going on. Would a FPR cause intermittent stalling?

 

[Bryce418]

The frp could cause issues, but I haven't ever seen one cause a no start. I don't think it's a bad idea at all to retrace your steps, even the best techs make mistakes.

 

[nh_duramax]

Thank you...I will look at it tonight.

 

[nh_duramax]

So far nothing. Is it possible for the CP3 pump to cause stalling? What should the fuel rail pressure be while cranking?

 

[nh_duramax]

found a cracked plastic bleeder screw tonight. i will pick one up and let you know if it fixed the issue.

 

[nh_duramax]

replaced the bleeder screw. it now starts but starts hard cold or warm. i monitored the fuel rail pressure while running. it was bouncing around between 5700 and 6300 psi. this sounds to low.

any thoughts on what the fuel rail pressure should be for a 2003 LB7.

 

[Bryce418]

That actually seems a bit high if memory serves. The big thing is if its staying with the desired frp#.

 

[chevyburnout1]

The idle pressure is normal. Have you watched the fuel pressure when cranking? It should jump up passed 2000psi pretty instantly. The injectors wont fire until minimum 1500psi is reached.

 

[nh_duramax]

the command FRP goes to 35MPa but the the actual FRP stays in single digits until it starts thengoes to 35MPa.it takes about 10-12 seconds of cranking to start. does this sound like the Fuel Pressure Regulator? Also, when you say the fuel pressure, I am assuming you mean fuel rail pressure, is that correct?

 

[Bryce418]

When the pressure climbs is it sudden or fairly gradual?

Sounds like it may be getting some air in the lines, or draining back but not so much as to cause a complete loss of prime.

You might try pumping up the system with the primer and see if you can find any leaks.

 

[chevyburnout1]

Yeah I'm talking about the rail pressure, my bad for not being as clear. Like what was just mentioned above air getting into the supply side can be one cause of that.

 

[nh_duramax]

pressure seems to come back all of a sudden when it starts running after considerable cranking. started it today with an outside temp of 30 degrees F. Started right up. ran it for 3-4 hours with my scanner (not the good one) while running it. I didn't shut it off for fear of not starting. pressure was around 4200-4400 psi at idle and would go as high as 20000 psi while driving. then at an intersection it died whil at idle. haven't been able to get it started since. I am not sure where to go next. Does it sound like the FPR or injectors?

 

[chevyburnout1]

When it dies is it instant? Like someone is shutting the key off? Or does it kinda chug down and die? Like someone pinching a fuel line.

 

[Bryce418]

The sudden climb points to a drain back or air leak issue. It could be the filterhead allowing drain back.

 

[nh_duramax]

it is fairly quick almost like the key shutting it off. definitely no chugging. I put my foot into it to try and save it but no response.