Hey guys,

I posted in another forum also and just trying to get some info.

I've had several fords and dodges but this is my first duramax. Overall I LOVE this truck.

So I bought my truck last month. After about two weeks I took it back to the dealer to have steps installed. On the way down the display notified me that the def was low. I had the dealer top it off while it was there. They told me that it only comes w 3g. They added 4g. This was at 1000m.

Then about three weeks later I got a CEL. When I checked in w Onstar they told me it was a code for inj 1 out of learning range. The def message showed up again on the way to the dealer.

The dealer replaced the inj and added almost 5g of def. This was at 3300m.

I'm concerned/bummed that the inj was bad at 3k but whatever. It's under warranty.

The thing that is really bothering me is the def usage. So far I've counted about 5-6 regens since I've had the truck. The first time it regen'd I couldn't figure out what was up w it because it was idling at 850-900.

I drive in LA traffic and usually do about 100-150m a day. The reports I read and what the dealer told me was that you shouldn't need to touch the def between oil changes.

This is now about 14-16g in half an oil change. I could understand using more if I'm towing, but I haven't even towed w it yet and honestly I've been driving it like an old lady. It hasn't shifted higher than 2200 yet.

I thought that maybe the regen's and def usage was from the bad inj but it just regen'd again today and it took about 45min to complete. This is 300m after the inj was replaced.

The last thing I am questioning is fuel mileage. It seems to regen about every 500m so it's killing my mileage. The first tank I averaged about 16. Then it stayed around 15.5. The last tank was 14.5. This is all hand calculated. My 99 dodge w twins sticks and fuel would average 14-15 and it had 225k on it.

Does anybody have any ideas? I really love the truck and just want to make sure everything is cool.

 

Emission delete the truck, and your fuel mileage will increase. Just my 2c

 

It's a Cali truck so not really an option. Plus I have the 120k warranty which is like to keep.

 

I do have some ideas about this.
That is a lot of DEF. By GM or any standards. I wonder if your DEF injector is working properly? Spraying too much? Bad NOX sensor?
Secondly, Our experience has been that there are 2 common triggers for regen. The truck will initiate regen once it reaches 44 grams of soot in the trap or travels ~700 miles since the end of the last regen. Whichever of these events occur first will start a regen. The regen seems to last until the soot load goes below ~10 grams or so and the driving conditions no long promote regen.
As far as how much fuel is used during regen; My best guess comes from the mileage adjustment I see under steady state operation. For instance. My trip this weekend averaged 19.7 MPG mixed over 700 miles. The truck entered regen at 700 and regen-ed for 40 miles. At the end of regen the DIC showed 19.2 MPG. If I'd done the 740 mile trip without regen at 19.7 MPG I would have used 37.56 gallons. At 19.2 MPG, I used 38.54 gallons - a difference of about a gallon or 2.6% more fuel.
Many people ask about mileage gains with our emission intact tuning. Most want numbers on mixed driving. Mixed driving can mean many different things to different people. With that said, a single wheel truck can generally manage 16-18 MPG mixed on stock tires with a reasonable driver. On the highway, MPG numbers as high as 23 MPG can be achieved at cruising speeds near 60MPH. As speed increases past 70 MPH, mileage closer to 20/21 is the norm. Colder temps will hurt mileage, especially if the truck is short-tripped.

 

Great info. I'll keep an eye on the def use for the next couple tanks. I seem to be starting the regen closer to 500m.

What kind of gains can be seen from the emissions tune?

Feel free to pm me if you would like.

Thanks again for your reply.

 

i believe the DEF is used all of the time and not just during regen

it would make sense with a bad injector that it would be injecting more DEF to compensate. maybe there is another bad injector in there that has yet to trip any codes. possibly the 9th injector???

 

skav,
Here is what our tunes look like for the LML.
1. Optimized Stock -Power delivery smoother than stock with near stock output -Refined timing tables for lower EGTs and higher efficiency
2. Heavy Tow Tune (+40)-Built for towing loads from 8000lbs to gross vehicle weight
3. Light Tow Tune (+55HP)- Built for towing loads under 8000lbs
4. Sport Econ (+110)-High performance street tune designed to balance performance and reliability-Throttle sensitivity increased for less throttle input, quicker shifting and less average RPM in daily driving situations
5. Race Tune (+135)- This tune represents the maximum effort a Duramax engine equipped with a stock turbo and stock injectors. A FASS 150 lift pump and gauges are highly recommended

2004LB7,
You are correct. DEF will spray whenever the NOX sensor triggers it. Here is a great resource for emissions equipment:
https://www.chevrolet.com/content/da...radoHD_DEF.pdf