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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29430
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I'm having the same problem, expect mine only doesn't start

Customer Question

I'm having the same problem, expect mine only doesn't start when it's warm. Are been running. Starts right up and runs fine cold.
Submitted: 1 month ago.
Category: GMC
Expert:  Amedee replied 1 month ago.

Hello and welcome!

My name is ***** ***** I can assist you with your question.

Expert:  Amedee replied 1 month ago.

I will try my best to answer all of your questions.

However, before we get started, please let me mention a few things.

1. If at any point you would like to speak on the phone, please feel free to request a phone call on your end and I can call you right away.

2. If you dont understand any technical terms or anything that I mention (component tests or theory or operation), please let me know and I will provide you with a more in debt explanation or answer.

3. Please understand that I am here to help you anyway I can.

Can I start by getting the codes in the computer and the VIN?

Thank you!!

Customer: replied 1 month ago.
Camshaft sensor , 7 glow plugs out
Customer: replied 1 month ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Amedee replied 1 month ago.

Can I start by getting your VIN?

Thank you!

Customer: replied 1 month ago.
Phone call.
Customer: replied 1 month ago.
I'm not plugged in to a computer right now. I can tell you exactly what it's doing
Expert:  Amedee replied 1 month ago.

Is this a diesel engine?

Customer: replied 1 month ago.
We replaced oil sending unit, primer pump and filter. Checked breakers. I read on hear about a fuel check valve, that makes sense
Customer: replied 1 month ago.
Expert:  Amedee replied 1 month ago.

Is this an electrical issue or an engine performance issue?

Customer: replied 1 month ago.
It's 20 degrees right now, I can walk out and crank it right up , no problem
Customer: replied 1 month ago.
Can't tell, runs fine.
Expert:  Amedee replied 1 month ago.

Sir, I did not know this engine was a diesel engine. I dont have any experience with diesel engines.

I am going to leave this open for other experts that have more knoweldge on these vehicles.

Thank you for your patients..

Customer: replied 1 month ago.
Ok, I'll be getting vin and codes ready
Expert:  Gm Tech (Cam) replied 1 month ago.

When you get the VIN and code I can help you.

Customer: replied 1 month ago.
I wrote all that down somewhere. Let me get it. I think it's going to be the cam shaft sensor. Because when we pull it out of block it does the same thing. Turns over and tries to hit but want start.
Expert:  Gm Tech (Cam) replied 1 month ago.

ok thanks. knowing Exactly which engine and such will be vital to me helping you.

Customer: replied 1 month ago.
I understand. It's going to be about 30 minites
Expert:  Gm Tech (Cam) replied 1 month ago.

sure, no problem.

Customer: replied 1 month ago.
1gchk23d66f202631
Codes-
0340
0522
P0087
Expert:  Gm Tech (Cam) replied 1 month ago.

The code I am concerned with is the P0087, that is a low fuel rail pressure code. Have you done a return flow test? These injectors use some of the high pressure fuel to operate the injector. If that part of the injector is flowing too much, it will lower pressures, making it hard to start when hot.

Customer: replied 1 month ago.
I've been told that. We are just trying to check everything before we go that route.
How do we do the test?
Expert:  Gm Tech (Cam) replied 1 month ago.

You need to remove the return line from each injector, then measure the flow out if each injector one at a time after 15 seconds cranking. More than 3cc is too much. Honestly that is the most likely issue. Second would be a weak injection pump.

I know both are expensive options, but hard start when cold is usually only one of those.

Customer: replied 1 month ago.
I'm sorry, what is most likely again?
Customer: replied 1 month ago.
Mine is hard start when hot
Expert:  Gm Tech (Cam) replied 1 month ago.

Sorry, fingers got ahead of brain, needing more coffee. When hot, fuel in thinner, metal expands increasing tolerances.
Most likely is a couple of the injectors.

Customer: replied 1 month ago.
How would Increased tolerance effect losing prime on an injector after 30 minutes of run time?
Customer: replied 1 month ago.
I understand fuel thickness. But only cooling down from 190* to 120* could make it start and run perfect?
Expert:  Gm Tech (Cam) replied 1 month ago.

The injectors are not each individually primed, rather this is a common rail fuel system. The pump only supplies high pressure fuel to the whole system. a leak of any kind, external, or internal due to an injector issue or weak pump will lower the pressure. these need about 4500psi JUST to start. IF they only get say 3500, it won't. Cool it down, fuel is thicker, metal cools, and you get slightly higher pressure, enough to start. Then once the speed of the engine picks up, it can overcome that internal leak.

Expert:  Gm Tech (Cam) replied 1 month ago.

Gm ran into the same sort of issue on the firs series of Duramax Engines, but those ended up needing all the injectors due to a flaw in design. Yours is a newer style and that systemic flaw has been fixed. even though, a couple worn injectors would do exactly this.

Customer: replied 1 month ago.
Ok. Makes sense... Then why can I sit there with starting fluid and and wd40 and get it to run hot, but not stay running once I stop applying them?
Expert:  Gm Tech (Cam) replied 1 month ago.

Ok, I missed the part originally about not staying running, I read into your issue as it simply didn't start when hot. So spraying an outside fuel also does not make it stay running?
When you cool it down and it starts, does it shut off on its own or will it stay running then until you stop it?

Customer: replied 1 month ago.
Runs like a new vette!
Expert:  Gm Tech (Cam) replied 1 month ago.

Ok, the second item to check is the cam sensor wiring. I see you changed the sensor, so we need to check the wiring for chaffing on the engine block that could be grounding it out.
I still suggest the injector test, I feel that is vital to either confirm or rule out.

Customer: replied 1 month ago.
sir. Have not changed out sensor yet. On order. Will do fuel test in the meanwhile. I'll let you know. Can I get back with you next week?
Expert:  Gm Tech (Cam) replied 1 month ago.

Sure thing. Save the link to this page as a favourite and reply back to it then. I may not be online when you reply, but will get an email, which I will reply to when I can.
If you find any injector over that spec, 3cc, you will need to change it. If you have all around 3 and maybe 1 or 2 at 4cc, that should not cause this much of an issue. I expect you will find one with much higher than that.

Customer: replied 1 month ago.
10-4 thank you
Expert:  Gm Tech (Cam) replied 1 month ago.

Your Welcome.