Any Duramax Gurus on here?

zayne2427 · Jan 27, 2016

Bought my first Duramax and having a few issues. I'm a Cummins guy so don't much about the duramax's. It is a bone stock 01 LB7 3500 and it is losing the throttle pedal.
Driving down the road and the throttle pedal just quits working. Still idlea just throttle does not work( drive by wire).
Also truck has always got around 17 mpg empty and 12 loaded down. Pulling an empty trailer to Illinois today it got 11mpg and 10.5 loaded on the way back. Truck seems sluggish as well.

Not sure if the issues are related to each other.

Truck throws zero codes.
I have replaced the throttle pedal
Thanks for any help

matth_85 · Jan 27, 2016

I am going to say an injector issue. I have seen them have a similar issue with injector problems. Put it to the floor and it goes to limp mode. Odd that it isn't throwing a code though. Typically they do that before you see an issue.

zayne2427 · Jan 27, 2016

Crazy thing is.. Sometimes it will do our running down the interstate, lose the pedal, let the rpm go down then it refers itself. Sometimes you have to completely shut off the truck and wait a min, start it up and good as new.
It is so sporadic it has done it anywhere from 5, 15, 30, 50, 70 mph...

muddinmetal · Jan 27, 2016

zayne2427 said:
Crazy thing is.. Sometimes it will do our running down the interstate, lose the pedal, let the rpm go down then it refers itself. Sometimes you have to completely shut off the truck and wait a min, start it up and good as new.
It is so sporadic it has done it anywhere from 5, 15, 30, 50, 70 mph...

Throttle body or the wiring going to it

kboring · Jan 27, 2016

zayne2427 said:
Crazy thing is.. Sometimes it will do our running down the interstate, lose the pedal, let the rpm go down then it refers itself. Sometimes you have to completely shut off the truck and wait a min, start it up and good as new.
It is so sporadic it has done it anywhere from 5, 15, 30, 50, 70 mph...

Have you changed the fuel filter?

If you have and still have problems, get a scanner and check the fuel rail pressure. Sounds like it could have low rail pressure. More than likely its cp3 related. The cp3s on those lb7 are bad about taking a crap around 200k

Could also be bad fprv causing low rail pressure and truck to limp. Does it surge at idle?

kboring · Jan 27, 2016

muddinmetal said:
Throttle body or the wiring going to it

A diesel doesn't have a throttle body - or even a throttle blade

zayne2427 · Jan 27, 2016

Does not surge at all. It's just like you flip a switch and the gas pedal doesn't work. Truck has 119k miles

rpf500 · Jan 27, 2016

Check battery cables and make sure there tight. I've seen 2 doing this and both stopped after cables were tightened.

Google Duramax APPS. Accelerator Pedal Position Sensor.

Pretty common issue. I have my best luck using Duramax forum.com.

MoparMan · Jan 27, 2016

kboring said:
A diesel doesn't have a throttle body - or even a throttle blade

Not sure about others but 6.7 Cummins does have a throttle valve.

kboring · Jan 27, 2016

Like won't rev at all? Sits at idle? or just dead feeling - won't rev past 2k and revs very slow?

First thing like mentioned above, check grounds & battery cables.

If they're good I'd change the fuel filter and clean the MAF. If it has a k&n filter throw it away and get a stock one. The oil on the filter can get on the MAF and make it act stupid.

If you still experience the problems after that I'd get a tech II and check the rail pressure.

zayne2427 · Jan 27, 2016

Sits at idle... Zero throttle at all... Going to check cables, grounds, and apps plug in the morning and see if it helps anything

kboring · Jan 27, 2016

10-4 sounds like a good idea. If it drops to idle it's not rail pressure related.

BUG-E J · Jan 27, 2016

When mine does that fuel filter fixes it.

NewMarketJeep · Jan 28, 2016

Fuel filter

Throttleout · Jan 28, 2016

Possible collapsed fuel suction lines, filter housing letting in air, fuel pressure reg stuck open, injector return rate to high, injection pump going out, loose connection to fuel suction valve.

Zjman · Jan 28, 2016

Hope he doesnt mind but a guy on here goes by username sting. He makes a living by working on dmax and even raced em. Good dude too Id pm him if u cant figure it out U can fix most dmax issues by buying a powerstroke fyi

Sent from my iPhone using Tapatalk

Sting · Jan 28, 2016

Sounds like the TPS (throttle pedal) is going bad. There is 3 sensor in the pedal and if one gets a bad spot it will do that. Easy to change and about 70 bucks or so. I would scan the computer and see if there is a code. If you have any problems give me a call. 740-689-0606 Jeff

Sting · Jan 28, 2016

I think everyone should own a powerstroke!!!!! I make a good living working on them also. lol I just finished a excursion 6.0 head gasket job and delete. Now I can afford the Hardline Crawler trip. I had to kick you Zman. Thanks for the good words also.

zayne2427 · Jan 28, 2016

Sting said:
Sounds like the TPS (throttle pedal) is going bad. There is 3 sensor in the pedal and if one gets a bad spot it will do that. Easy to change and about 70 bucks or so. I would scan the computer and see if there is a code. If you have any problems give me a call. 740-689-0606 Jeff

I replaced the throttle pedal first thing with a factory part from GM, also scanned the computer and the only codes are.
Intake air heater A circuit- P0540
Glow plug heater circuit A
The stud bolts the wiring for the glow plugs is lose and is throwing a code for the glow plugs

jmh78 · Jan 28, 2016

Not duramx but my 2500 HD with 6.0 would do exact same thing. I replaced pedal, module on firewall and still occured. Finally figured out it was throttled body. It had two throttle position sensors and they did not agree on where the butterly was in travel and would cause truck to go into limp mode. Could be rolling down hwy bump it into neutral shut the switch off and start it back and all was fine for another random amount of time. Ended up replacing throttle body.