GMC Troubleshooting Questions? Ask a Mechanic for Answers
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Can I start by getting the codes in the computer and the VIN?
Can I start by getting your VIN?
Is this a diesel engine?
Is this an electrical issue or an engine performance issue?
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..
When you get the VIN and code I can help you.
ok thanks. knowing Exactly which engine and such will be vital to me helping you.
sure, no problem.
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.
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.
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.
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.
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.
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?
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.
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.