Duramax towing “engine reduce power”

Willyracer · 06-28-2021, 11:09 PM

I was towing from Cincinnati to BG. When I hit the hills of Ky my
truck shut down with the reduce power limp mode.
Had the truck towed home. I have replaced the fuel pressure
Relief valve. Also installing a Air Dog fuel lift pump and replace the 6”
Rubber fuel supply hose at the motor.
Just trying to cover all the bases
Has anyone else had this problem?
Truck runs good with no problems without trailer .

Thanks for any suggestions
David

voltdr · 06-29-2021, 12:00 AM

Does it give any DTC codes? Mine did it and I would get "low pan rail pressure". I tried everything, lift pump, relief valve. The only thing that fixed it was replacing the injectors. I know that's not what you wanted to hear but I fought it for awhile before replacing the injectors.
Dan

Willyracer · 06-29-2021, 02:33 PM

I think the code was PO 87. and a code for high intake
air temperature
We was able to place a scanner on it while I was having
trouble and all the injectors was balanced and appeared to
be good.
But I not a diesel mechanic . If problem happens again
I was thinking injectors or cp3 pump. Both $$$ repair not
knowing for sure which is bad.

Thanks
David

NSSGTO · 06-29-2021, 02:59 PM

Which model Duramax? I have had that issue on LLY's and it is usually the relief valve. Replacing them seems to help for a short time. I have found shimming the original with a .040-.060 washer works well.

Willyracer · 06-29-2021, 07:24 PM

It is a 2008
I found a shop that changes the valve from a 2 stage
Valve to a single stage.
The 2 stage opens at a high pressure and stays open till
The pressure drops below a low pressure setting

The single stage opens and closes at same set point

That my understanding of how the valves work.I could be
mistaken on operation of the valves

Bob Gullett · 06-29-2021, 11:56 PM

On my LBZ 2007 Silverado was getting a low fuel pressure code. And would only happen when towing the trailer. Took it to a friend who has lots of experience with these engines and run a diesel repair shop. Replaced the injectors and problem cured. Not sure if this is the same issue you’re having but thought I’d share my experience.

voltdr · 06-30-2021, 09:38 AM

Mine is also an LBZ. I bought a tuner that would check balance rates too. But it only checks them up to 1500 RPM. I also installed an AirDog system. The only thing that fixed it was replacing the injectors. I was told that it has to do with how much fuel was being returned .
Dan

Willyracer · 06-30-2021, 03:32 PM

Thanks, can the injectors be sent and tested or is it a waste
Of time and just replace the injectors?

Looks like injectors are 350 to 450$ each for reman.

06-28-2021, 11:09 PM	#1
Willyracer Junior Member Join Date: Feb 2019 Posts: 87 Likes: 7 Liked 57 Times in 24 Posts	Duramax towing “engine reduce power” I was towing from Cincinnati to BG. When I hit the hills of Ky my truck shut down with the reduce power limp mode. Had the truck towed home. I have replaced the fuel pressure Relief valve. Also installing a Air Dog fuel lift pump and replace the 6” Rubber fuel supply hose at the motor. Just trying to cover all the bases Has anyone else had this problem? Truck runs good with no problems without trailer . Thanks for any suggestions David

06-29-2021, 12:00 AM	#2
voltdr Senior Member Join Date: Jan 2008 Location: Texas Posts: 700 Likes: 77 Liked 87 Times in 47 Posts	Re: Duramax towing “engine reduce power” Does it give any DTC codes? Mine did it and I would get "low pan rail pressure". I tried everything, lift pump, relief valve. The only thing that fixed it was replacing the injectors. I know that's not what you wanted to hear but I fought it for awhile before replacing the injectors. Dan __________________ Dan Foley SC 4698

06-29-2021, 02:33 PM	#3
Willyracer Junior Member Join Date: Feb 2019 Posts: 87 Likes: 7 Liked 57 Times in 24 Posts	Re: Duramax towing “engine reduce power” I think the code was PO 87. and a code for high intake air temperature We was able to place a scanner on it while I was having trouble and all the injectors was balanced and appeared to be good. But I not a diesel mechanic . If problem happens again I was thinking injectors or cp3 pump. Both $$$ repair not knowing for sure which is bad. Thanks David

06-29-2021, 02:59 PM	#4
NSSGTO Junior Member Join Date: Feb 2010 Posts: 58 Likes: 10 Liked 27 Times in 18 Posts	Re: Duramax towing “engine reduce power” Which model Duramax? I have had that issue on LLY's and it is usually the relief valve. Replacing them seems to help for a short time. I have found shimming the original with a .040-.060 washer works well.

06-29-2021, 07:24 PM	#5
Willyracer Junior Member Join Date: Feb 2019 Posts: 87 Likes: 7 Liked 57 Times in 24 Posts	Re: Duramax towing “engine reduce power” It is a 2008 I found a shop that changes the valve from a 2 stage Valve to a single stage. The 2 stage opens at a high pressure and stays open till The pressure drops below a low pressure setting The single stage opens and closes at same set point That my understanding of how the valves work.I could be mistaken on operation of the valves

06-29-2021, 11:56 PM	#6
Bob Gullett VIP Member Join Date: Mar 2002 Posts: 1,069 Likes: 41 Liked 414 Times in 92 Posts	Re: Duramax towing “engine reduce power” On my LBZ 2007 Silverado was getting a low fuel pressure code. And would only happen when towing the trailer. Took it to a friend who has lots of experience with these engines and run a diesel repair shop. Replaced the injectors and problem cured. Not sure if this is the same issue you’re having but thought I’d share my experience. __________________ 68 Chevy11 327 F/S

06-30-2021, 09:38 AM	#7
voltdr Senior Member Join Date: Jan 2008 Location: Texas Posts: 700 Likes: 77 Liked 87 Times in 47 Posts	Re: Duramax towing “engine reduce power” Mine is also an LBZ. I bought a tuner that would check balance rates too. But it only checks them up to 1500 RPM. I also installed an AirDog system. The only thing that fixed it was replacing the injectors. I was told that it has to do with how much fuel was being returned . Dan __________________ Dan Foley SC 4698

06-30-2021, 03:32 PM	#8
Willyracer Junior Member Join Date: Feb 2019 Posts: 87 Likes: 7 Liked 57 Times in 24 Posts	Re: Duramax towing “engine reduce power” Thanks, can the injectors be sent and tested or is it a waste Of time and just replace the injectors? Looks like injectors are 350 to 450$ each for reman.