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I have a 2005 c4500 with a Duramax ,periodically it will…

Customer Question
I have a 2005...

I have a 2005 c4500 with a Duramax ,periodically it will crank no start snap on scan tool data says ptoengine shut down signal Yes

Mechanic's Assistant: Will the headlights turn on? Is the battery fully charged?

Is this the reason? rail pressure is good yes cranks fine headlights on

Mechanic's Assistant: What is the model of your '05 Chevy?

C4500

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

Yes im a mechanic, I replaced cam sensor, snap on scanner shows no codes

Submitted: 3 years ago.Category: Medium and Heavy Trucks
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Answered in 2 hours by:
7/2/2019
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago
Mike Mcmillan
Mike Mcmillan, Shop Foreman/Triage Tech
Category: Medium and Heavy Trucks
Satisfied Customers: 6,790
Experience: Volvo/Mack Master Tech, Certified with Cummins, Eaton, GM, Hino, Detroit Diesel
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Hello and thank you for using Just Answer. My name isSteve and I will be assisting you with your question. Can you please let me know what the rail pressure is while this is cranking as well as what the ecm voltage is dropping to? Thanks
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Customer reply replied 3 years ago
the rail pressure bounces between 5800 and 6200 psi,the ecm volts drop to around 10.8 volts when cranking.
all the readings stay the same when it does start, I thought it was fuel leaking back issue replaced the filter head and some fuel lines that were suspect looking, still the sameif it is fuel leaking back issue wouldn't my rail pressure be low?hello?
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago
I am hear. Our availability varies based on workload and time away from family. I will do my best to respond in a timely fashion. The rail pressure would be slow to build if it had a drain back issue. What kind of body does this have on it? Is there a physical pto on it?
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Customer reply replied 3 years ago
no no PTO it has a dump body on it, it started now and Scanner still says PTO engine disable yes so that is not the issue.
it has been acting like this for about a month, you can crank and crank no start walk away for five minutes come back and it will start,or give it a shot of either and starts, it will start every time the rest of the day sits over night and sometimes starts some time not, it never quits once it is running,we have 80 degrees so not glow plug issue and has good power when running ,I checked all wiring to ficm and cant see any chafing,thinking the ficm could be bad but don't want to throw money away
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago

Okay, I am going to post a bulletin for this here, Give me a moment, Usually when the PTO causes an interference it will not allow the unit to crank, Because at times the upfitter wiring can short and cause an issue

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Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago

Here is one of them

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Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago

Make sure you are getting a good consistent CKP signal also, because sometimes these sensors will get to the point that they are weak and will not produce the right amount of voltage until they hit a certain speed which using ether to start it only helps combustion and takes the load off of the engine spinning which increases cranking rpms which will allow the threshold to be met. Please let me know if you have any follow up questions on this. Thank you

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Customer reply replied 3 years ago
I am convinced it is not the PTO causing this.according to the scanner I have good crank shaft sensor pulses along with cam shaft sensor as well .
what else can cause the ficm to not fire the injectors
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago

Have you drained the rail to relief the pressure to make sure you do not have a biased sensor?

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Customer reply replied 3 years ago
it drops down to around 140 in about 10-15 seconds after cranking
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago
It shouldn’t do that. That pressure should maintain. Do you know what the balance rates are after this is running? Do you have the return flow kit?
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Customer reply replied 3 years ago
I can check ballance rates , I do not have a return flow kit
Customer reply replied 3 years ago
Balance rates are as follows Cyl 1 is 3 cyl 2is4 cyl 3 is 0 cyl 4 is -1 cyl 5 is -1 cyl 6 is -1 cyl 7 is -2 cyl 8 -s -1 this at an idle because now the truck is starting , the rail pressure still drops to 150 or so when truck is not running start to crank pops right up to 6000
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago

I would say that you either have an injector over returning or a limiter issue. You have everything else you need by the way it sounds. If you use ether and it kicks over that is again allowing the engine to turn a little bit faster rpm which is allowing the output of the pump to spike a little bit

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Customer reply replied 3 years ago
I mshould only need about 3000 psi to run correct? what limiter issue are you talking about?
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago
The relief valve is the fuel limiter. If you have a fuel pressure decay as bad as what you are saying that issue needs to be addressed. If your not getting the volume you need to fluently fire the injectors it is not going to start
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Customer reply replied 3 years ago
but if pressure is way obove minimum limit while cranking it should have volume, and on another forum frp droping to 150 after cranking is not uncommon
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 3 years ago
On the LB7 that was acceptable. This is not the engine that you have. Pressure is caused by flow with restriction. When we have had issues like this over the last 17 years as long as the ckp and cmp wavelengths are good and in sync and there is no other faults present then you have a fuel issue. A ficm would have present faults in the ecm and vise versa and would still not fire based on using ether or not
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Customer reply replied 3 years ago
although it appeared to be cranking fast enough it was not ,Had to put ground cable from starter bolt to frame
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