Here it comes, diesel guys

Roberto Diagnostician Fremont, California Posted   Latest  
Unsolved
Carquest
CTI - Carquest Technical Institute
Trained By Techs
Driveability
Heavy Duty
2015 Chevrolet Silverado 3500 HD LT 6.6L (8 LML) 6-spd (6L90) — 1GC4KZC88FF593758
No Start Hot
Crank / No Start

Ok guys there it goes, this truck has a non-start condition when is hot, we let it sit overnight and in the morning starts just fine, drives fine with no driveability issues, once you turn it off, truck will crank but no start until is cold again, pressure on the rail reads over 1000 psi when cranking, the only thing is Am not sure how much voltage this injectors need to operate, I know on Fords FICM sends 48 volts, but I don't know on this truck, of course I'll find out how much voltage they need, my lead technician said that when he check the voltage was at 55 volts, we will check it in the morning, as you can tell, we don't have much experience on duramax but we wil get there, and guys, don't be too hard on us, and one more thing, we know that this motors are known for a problem on the high pressure pump and that the high pressure side will no build up when that happens, but remember, we have over 1000 psi when cranking and don't starts, where we go from here? I'll update on this issue as we progress, thank you guys for the input in advance.

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Martin Diagnostician
Burleson, Texas
Martin Default
 

Any codes stored?

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Chris Owner/Technician
Lorena, Texas
Chris Default
   

Rail pressure on a 6.6 duramax should be at least 2500 to make the injectors fire and engine start. I bet your looking at a bad high pressure pump. but don’t take my word for it I focus mainly on cummins... :)

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

There is a pretty good change the high pressure fuel pump is not working correctly. I like to see 5000 psi when cranking. I wouldn't be worrying too much about the injector voltage, since your rail pressure is too low. Let the vehicle sit over night and cool off. Once its started, bring up the engine and fuel temperature to the normal operating temps. At idle, command the rail pressure up as…

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Roberto Diagnostician
Fremont, California
Roberto Default
 

Thanks for the reply Albin, but no there are no codes on this truck, will follow your advice and see what the results are, I'll keep you guys updated.

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Jim Technician
Dover, New Jersey
Jim Default
 

Look for a cylinder with too much correction. I would then test injector returns, targeting on that bank and finally that cylinder. I suspect you have a bad injector. On a Duramax you need I believe its 4000psi to start. A bad pump should cause low pressure at all times. Not just some events. But dont rule out the pump, especially on a neglected truck.

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Andrew Technician
Odessa, Texas
Andrew Default
 

Make sure you check basics . Make sure you have good vacuum while cranking . Put a gauge on the fuel port located at the front of the engine. It will have a cap that you twist off and install a gauge to get your readings. If you dont have that adapter for the fuel fitting. I would just remove the fitting off the line and put a rubber hose over the brass line and get your readings that way. Once…

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Scott Owner
Moreno Valley, California
Scott Default
   

Hi Roberto, A thousand PSI is too low for this to start. There needs to be a minimum of 1,888 PSI of pressure with the engine cranking. I'd use chart - Engine Cranks But Doesn't Run Document ID: 3995965 Have you hooked a gauge to the fuel rail service port? Have you tried to prime the vehicle to 10 PSI and see if it starts? Engine cranking is the gauge reading less than 6" Hg? If those tests…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Exactly Scott. All of the service information steps are simple to follow to diagnose this system quickly and failures are well-documented. The onset of the pump failure scenario on this system often results in debris trapped in the regulators that control the rail pressure.

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Martin, As you aptly stated in your post, we're determining fuel quality, cranking/batteries, supply, or high pressure to determine the no-start issue. Following the charts will lead you where the fault is. The only other thing I could add to this - I'm not seeing as many "pattern failures" as I used to, but this fuel system is as close as it gets today. I've noticed that if Roberto's…

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Marlin Technician
Estacada, Oregon
Marlin Default
 

I disagree with the "steps are simple to follow" statement. This is a 2015 model; some of the steps are a serious, time-consuming pain to follow. Performing the inspection in the TSB takes many hours. The system design and the TSB are quite stupid, IMO.

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

We didn't design the system or break it, but have to diagnose and repair it. The steps are designed to cover all of the bases during the diagnosis Marlin. Personally, I have a complete dislike for diesels, yet I've been working on them since my teens and they have made me bucket loads of money. One of the most prevalent issues with technicians these days is a general unwillingness and frequent…

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Marlin Technician
Estacada, Oregon
Marlin Default
 

I agree that the system is just what it is. One of the problems with the TSB is that it just piggy-backs the SI, which doesn't really included the possibility of the HPP failing is it typically does. Furthermore, the photo of the FPR1 looks like it was staged, not matching real failure conditions. How did the metal get above the o-ring, but the screens are clean? Why not address what to do…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Marlin, I find a lot of things "stupid" in today’s society. I won't go into the details of stupidity that are being thrown at us by greedy and unknowledgeable legislators, but...Everyone has an agenda. Have you noticed that the exhaust systems on today's diesels have surpassed what replacing an engine used to be on an ordinary gas vehicle from not too long ago? Have you noticed that the…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Well said Scott! Darn near everything today is scrutinized so heavily for possible liability issues and that is what a lot of the "stupid" stuff is grounded in. CYA statements and procedures with specific validated steps abound for reasons that may seem unreasonable to some, but necessary for others. FWIW, I think that the same engineer who designed the diesel DEF system and escalating…

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Marlin Technician
Estacada, Oregon
Marlin Default
 

Yes, I have thought about all of that. Really, the primary blame should go to the consumers, They want stupid power in little vehicles, and they want to strip them of all semblance of consideration for the rest of the people on the planet. THIS drives what we have today. The manufactures know how to makes these vehicles reliable, but the power war and consumer's bent to destruction are…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Roberto. You can find the TSB that Scott listed and which may be relevant to the system condition with a simple Google Search. f01​.​justanswer​.​com/Bluegorilla/53…​.​pdf You may or may not have the conditions as per the bulletin, so use the bulletin and diagnostic procedures from the listed documents, as required. There are no short cuts. Your tech needs…

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Martin Instructor
Burnaby, British Columbia
Martin Default
   

Hi Roberto. Before I forget, the truck has an Allison 6 speed (MW7). What does your service information system tell you about this truck? Have you reviewed published bulletins on this truck fuel system? Without accurate information, you will surely go down a "rabbit hole". Basically, your rail pressure is too low when cold. Cold starting RPM values are lower than hot starting RPM, because to…

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Helpful
David Diagnostician
Independence, Louisiana
David Default
 

So this truck runs good after it finally starts? If so, you have to understand these fuel systems work on high pressure and low volume. If there is any leak in the high pressure system (i.e. injector retuning too much fuel) cranking is where the problem will most likely show up. The pump can't overcome the volume leak to build pressure with just cranking speeds. Plug each individual injector and…

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Matt Educator
North Canton, Ohio
Matt Default
 

You need more than 1000 psi to start. I've seen some start as low as 1500 but should be well above that. I usually see just the opposite symptom that youre describing, (hard start after sitting but will start after warm up). I would want to know why you're only building 1000 psi first. I'll repost if I think of anything that might help.

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Marlin Technician
Estacada, Oregon
Marlin Default
 

This seems as though a leak is occurring. When the faulty component, likely an injector, is hot, combined with being fed warm fuel, the fuel viscosity drops drastically, resulting is more leakage. The injection pump has very little excess capacity, so it quickly cannot build enough pressure.

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Robert Owner/Technician
Derry city , United Kingdom
Robert Default
 

do A leak back test on injectors that should sort you

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Roberto Diagnostician
Fremont, California
Roberto Default
 

Ok guys, thank you for your tips, most likely you are correct with the pressure loss, as you can see on this video, truck was running and pressure was normal at about 4300 psi or so, once I turned it off and crank it to start again it just won't start, and the pressure is low at about 1200 psi, now, my guy is asking me what should be the way to check where is the loss of pressure, is there a…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Roberto, What's wrong with starting with - the Engine Cranks But Doesn't Start chart? We can throw all the ideas we can out, but following this will lead you a logical conclusion of where the fault is.

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Roberto Diagnostician
Fremont, California
Roberto Default
 

Hey Scott, thanks for the input, the service information you describing, where do I see that information? I have an account on GM but is this information available on GM only or Mitchell, Alldata have it?, Thanks

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

You can find that information in Alldata, Mitchell and even Identifix.

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Roberto, I 'm not sure that I understand what you mean by " I have an account on GM". Various services are available separately or packaged, which may be SI, GDS 2, SPS, Tech2Win and other. If you have paid access to GM Service Information and other functions via ACDelco Techconnect, then all of the documents that both Scott and I took the time to list above, will provide you with the pathway…

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Marlin Technician
Estacada, Oregon
Marlin Default
 

You seem to be trying to diagnose this without using service information. Most of the replies which you received were written with the obvious in mind- you will follow the routine testing procedure as provided in SI. Testing injector return flow is about as ordinary in diesel engine service as testing ignition coils is in gasoline engine service, so we just assume knowledge of how to do…

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Cliff Diagnostician
Santa Maria, California
Cliff Default
 

If you suspect an issue with the high pressure system it should show up in the fuel filter... Way faster to pull the fuel filter and cut it open with a tubing type cutter than to gain access to the FPR1.

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Cliff. The fuel filter is a good place to start to get a glimpse of what has been attempting to, or may have passed through the filtration media. However, an issue with gaining access at the filter, is that for accurate results the complete filter assembly should be removed and inverted. Then the housing should disassembled to identify whether the debris is on the inlet side (outside) or…

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Harm Technician
Fergus, Ontario
Harm Default
 

We ran into this with my dads 2011 duramax. Truck ran ok and started fine when cold. Went on a big work trip and shut truck off at the border. would crank and not start. not enough rail pressure. was at a GM dealer in buffalo for days. The service advisor there had called me multiple times. What ended up being the problem was that a fuel station the fuel tanks were topped up with gas. So a 1/4…

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