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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Having fuel pressure problems, on a 2011 lml duramax

Customer Question

Having fuel pressure problems, on a 2011 lml duramax
Submitted: 1 year ago.
Category: GM
Expert:  GM Tech (Cam) replied 1 year ago.

Hi there, I am Cam. Can i get your first name pleasE?

wIth your truck, do you get any codes set with it? P0191?

Customer: replied 1 year ago.
I would like a different tech, my last question just last week you never answered it wouldn't let me rate you and I still got charged!!
Expert:  GM Tech (Cam) replied 1 year ago.

OK.

Expert:  GM Tech (Cam) replied 1 year ago.

I had a medical emergency at that time, and for some reason no ones decided to help you out, and for that I am sorry. I and none of my co experts are office people, we work in the shop and I can only assume that if no one else helped you, that they did not know how to help you. I am online now, and would like a great deal to help you solve your issue.

The one thing I thought I did ask was if you removed the Fuel pressure regulator #1 and checked it for metallic or other debris. Did you do that? If not, can you?

Customer: replied 1 year ago.
I checked it and it was clean, no debris or anything
Expert:  GM Tech (Cam) replied 1 year ago.

OK, your last question is not coming up, what was your cranking PSI?
I recall we tested some return fuel rate, and that you replaced the valve on the front of the drivers side fuel rail. "
Had we looked at the fuel pump itself?

Customer: replied 1 year ago.
I'm trying to send you videos of this but it's saying its to large
Expert:  GM Tech (Cam) replied 1 year ago.

Upload it to dropbox then send me the link.

Or put it on Youtube and same, send the link,

Customer: replied 1 year ago.
Okay let me see if I can figure that out
Expert:  GM Tech (Cam) replied 1 year ago.

ok

I will keep an eye out .

Customer: replied 1 year ago.
Okay I've been trying and it's not letting me upload it at all
Expert:  GM Tech (Cam) replied 1 year ago.

I am not sure what to suggest. Can you cut down the size?

Customer: replied 1 year ago.
What would cause me fuel pressure to drop to zero within 1-2 seconds after I kill my truck? Truck has to build fuel pressure from zero
Expert:  GM Tech (Cam) replied 1 year ago.

The system is not designed to hold pressure. It is designed to build the pressure during cranking. You know as well as any that it should build it inside of a second or so. You mentioned its not building high enough so we have to deal with a pump issue. You replaced both regulators so all that is left now is a faulty injection pump.

Customer: replied 1 year ago.
No I haven't changed the one on the pump nor the pressure sensors
Customer: replied 1 year ago.
When I kill my truck and the key is off it still say that my desire fuel pressure is 4351 psi
Expert:  GM Tech (Cam) replied 1 year ago.

It would not be a pressure sensor. Your desired fuel pressure will always be higher, even with the engine off, but that is not a problem. If we cannot get enough cranking pressure then we need to look at your injection pump as a possible issue.

Expert:  GM Tech (Cam) replied 1 year ago.

Here is a document I would like you to follow through.

Customer: replied 1 year ago.
can this test be done with a scan tool?
Expert:  GM Tech (Cam) replied 1 year ago.

No, you need a pressure vacuum gauge. The port top and Center by the thermostat housing is where you attach it. But you can use a generic gauge and detach the hose into the back of the port.

Customer: replied 1 year ago.
I will let you know soon as I test it and we will go from there
Customer: replied 1 year ago.
Okay the link you sent me, from #13 no start do I need to crank it with key on or off
Expert:  GM Tech (Cam) replied 1 year ago.

Crank it with the key normally as if you are trying to start it.

Customer: replied 1 year ago.
Okay so 1-12 with key off and 13 with key on
Customer: replied 1 year ago.
Will give a update ASAP
Expert:  GM Tech (Cam) replied 1 year ago.

Ok.

Customer: replied 1 year ago.
Okay I tested the FPR #2 and this is what I got. At idle I got about 48ml in 15 seconds and driving the truck down the road at 1800 rpm's I got about 2ml.
Expert:  GM Tech (Cam) replied 1 year ago.

2 ml at 1800 is perfect. Everything is pointing to a bad high pressure pump.

Customer: replied 1 year ago.
I did find a leaking/broke injector return line. I can grab it and it just pops off the injector, one of the little ears that goes around the injector is broke. I have a new injector return line kit for both sides ordered and it will be here tomorrow, after work I will put it on there and do the test on the injectors.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok.

Customer: replied 1 year ago.
13.5 when it says commanding fuel pressure, does it mean in park steadly gas it more and more making sure the pressures are within 100psi? At idle the pressures are within 100psi of each other and all the way up to 10-12,000 psi they are within 100psi of each other.. I haven't checked it any higher psi than that
Expert:  GM Tech (Cam) replied 1 year ago.

Yes it's all about verifying that commanded and actual throughout the range all are within 100 psi of each other.

Customer: replied 1 year ago.
When driving when I gas it all the way the commanded and actual psi gets like 10-12 psi apart from each other.. Do you have a email or cell phone number that I can send you the video of the scan tool
Expert:  GM Tech (Cam) replied 1 year ago.
is an email you can send it to. So commanded and actual always match, that is what we desire.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, it looks like at the higher rpm it does not match and that means the regulator 1 is bad on the pump. Now the fact you changed it means the pump is bad and unable to meet the high pressure needs.

Customer: replied 1 year ago.
I haven't changed the the regaulator #1 on the pump. I took it out and checked for metal and it was clean so I put it back in. I have only changed the FPRV #2
Expert:  GM Tech (Cam) replied 1 year ago.

Ok. Replace #1 and evaluate the issue. If it remains the. We move to the pump.

Customer: replied 1 year ago.
Okay thanks, ***** ***** you a update once I replace it
Expert:  GM Tech (Cam) replied 1 year ago.

Sounds good.

Please be sure to save this page as a favorite in your web browser so you can reply back to me easily. you can reply at an time, even after accepting or rating me.

Customer: replied 1 year ago.
With my psi being that far apart from each other when gased wide open, why ain't I getting a dtc for low psi or something? I'm gonna send you a few pictures of the scanner before I removed the FPS on back of fuel rail and cleaned it
Expert:  GM Tech (Cam) replied 1 year ago.

What was the substance on the unit?

Some of the issue might be the software in the scanner. Either way it's almost midnight and I get up at 6. I will log back on then.

Expert:  GM Tech (Cam) replied 1 year ago.

That looks like rust!, Did you find that anywhere else in the system?

Customer: replied 1 year ago.
No everything else looked clean, this time last year I had all 8 injectors and injector pump changed and that might have been on there from then. When I took the pictures was a week ago and the FPS really wasn't hardly tight at all but it's tight now
Expert:  GM Tech (Cam) replied 1 year ago.

OK, as long as your sure. If there is more debris or contamination in there, it would take out the whole system again. For now, lets change FPR #1 on the pump and see what that does for the pressure inconsistencies.

Customer: replied 1 year ago.
Do you have a diagnostic tests for fpr #2
Expert:  GM Tech (Cam) replied 1 year ago.

I will get what I have to you when I get to work in

Expert:  GM Tech (Cam) replied 1 year ago.

Ok, sorry I was driving to work. You have tested the regulator #2. IF you go back to the document, you will see that it explains when each is operational. #2 controls the pressure up to 1700 RPM. While I could not see the RPM on your scanner, I can assume based on your testing of the return rate that #2 is operating and when you compared actual to desired pressure, they matched at lower RPM and pressure. This all leads me to the conclusion that your regulator #1 is at fault.

Customer: replied 1 year ago.
When the motor is cold it starts better, once motor warms up its hard to start... With the motor just spinning over and over not starts if I hit the accelerator 4-5 times it will start up
Expert:  GM Tech (Cam) replied 1 year ago.

Understood Tye, we need to replace that regulator #1 as the diagnosis we have completed thus far points directly to that.

Customer: replied 1 year ago.
FRPR #1 is ordered and will be here tomorrow. Will let you know after while about the injectors test
Expert:  GM Tech (Cam) replied 1 year ago.

OK, sounds like a plan. Thanks for working with me. Cam certain with your determination we can get to the bottom of this.

Customer: replied 1 year ago.
Okay I'm testing injector returns. Engine at idle how much fuel should be returned
Expert:  GM Tech (Cam) replied 1 year ago.

3ml each for 15 seconds cranking or idling.

Customer: replied 1 year ago.
Would 10ml be to much or enough to cause a extended start
Expert:  GM Tech (Cam) replied 1 year ago.

Absolutely. How many injectors have 10ml?

these injectors use a bit of fuel to open the main injector, hence the allowable 3ml in 15 seconds. More than this is basically a fuel leak but its being returned to the tank.

Customer: replied 1 year ago.
Passenger side fuel return test
1- 10ml
2- 1ml
3- 2ml
4- 10mlDriver side fuel return test
1- 15ml
2- 2ml
3- 25ml
4- 25ml
Customer: replied 1 year ago.
Number one starts in the front of motor and number 4 is in back
Expert:  GM Tech (Cam) replied 1 year ago.

That shows me you have 5 that need to be replaced. This is a problem. You replaced them a year back, so that means that either they are bad out of the box or there is something that took them out, be it from the fuel system failure or from contaminated fuel.

Customer: replied 1 year ago.
Can something be wrong with ecm causing them to return to much fuel
Expert:  GM Tech (Cam) replied 1 year ago.

No, that is not controlled by the computer. That is a physical aspect of the injector. Returning too much is purely a mechanical issue in the injector. All the computer does is open the small solenoid that allows that fuel to be used to open or fire the main injection.

This leads me back to the why. Here is my new suggestion. With the junk you showed me in the fuel rail and on the sensor, and with your hard start issue, fuel pressure irregularities and now return rates, well let me say, if you were to have this in the dealer, I would be suggesting the replacement of the whole system and cleaning out the tank. The issue will be getting out the contaminants in the system. Its bad enough that GM just replaces it all to be sure they get it all.

Customer: replied 1 year ago.
What could cause contamination?
Expert:  GM Tech (Cam) replied 1 year ago.

Either from contaminated fuel or fuel system component failure.

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