3.0 L engine parameter confirmation

Dudeguyman · Sep 24, 2023

Engine data below I’m questioning and can’t seem to find anyone online posting hard data points. I don’t like to put my hands in CEL’s as issues can be found in advance and can help longevity which is the whole reason we buy engine data monitoring tools.

- 2020, 3.0 L, 40K miles, bought used 4K miles ago
- DPF differential pressure WOT: up to 33 kPa (330 hPa)
- DPF differential pressure idle: 1 to 2 kPa (10-20 hPa)
- EGT’s: 1250 to 1300 def F WOT
- Boost (WOT): 30 psia (atmosphere plus gauge pressure)
- Instantaneous mpg gauge/calculator fluctuation during steady throttle and inconsistent i.e. bouncing around between 27-33 mpg on flat road going 50 mph then 5 minutes late 20-25 mpg. During regen seeing 10-15 mpg less than what I typically would.
- Dealer says this gauge is a non-issue but my engineer brain says hell no I’ll figure it out for you.

I’m thinking clogged DPF? If it is clogged DPF, what caused that at low miles is the bigger question? Recently replaced radiator 1K miles ago and new transmission 2K miles ago, terrible luck but all warranty items.

TX_Critter · Sep 25, 2023

I saw your other post so watched the DPF delta pressure for a bit on my iDash, don’t normally monitor it. Highest number I saw was like 6 psig in hard acceleration from stopped, normal cruising was like 1-2 psig…

Mine is a 22 refresh lm2 with 18k miles and the DPF regen trigger was at around 85% during the numbers given.

Reading this post and your other one gives me the impression that you are way overthinking the whole thing, these trucks are smart enough to tell you if they are sick and if you are not seeing performance issues then what’s the problem.

Of the ones you listed boost is the only parameter I regularly monitor, and under hard acceleration it peaks around 25 psig. Which sensor are you taking your EGT number from (there are like 4)?

The trucks will definitely burn more fuel during regen, that’s how regen works.

Dudeguyman · Sep 26, 2023

TX_Critter said:
Mine is a 22 refresh lm2 with 18k miles and the DPF regen trigger was at around 85% during the numbers given.

Reading this post and your other one gives me the impression that you are way overthinking the whole thing, these trucks are smart enough to tell you if they are sick and if you are not seeing performance issues then what’s the problem.

Of the ones you listed boost is the only parameter I regularly monitor, and under hard acceleration it peaks around 25 psig. Which sensor are you taking your EGT number from (there are like 4)?

The trucks will definitely burn more fuel during regen, that’s how regen works.

EGT by the turbo, #1 I believe (on travel so don’t have numbers on me). If someone else is seeing 6.5 psig on DPF differential pressure, I’m reassured there - that’s pretty much where I’m at too. Research online states DPF differential pressure greater than 300 kPa (4.3 psig) is indicative of a blockage but these trucks are unique

.

Boost is still being low, 15 psig roughly, but bounces around and isn’t consistent - I’ve never had a turbocharger bounce around at peak before like this but also never had a diesel turbocharger as well. I’ll do a turbocharger leak check and call it quits on this subject.

Truck is under performing but dealership says this is all normal which is code for we don’t know. Dealership also said a massive knocking in my transmission is normal for diesels (whole new transmission a week later). This mpg thing drives me nuts, bought the truck performing well now I’m averaging 5-10 mpg less and it all started when truck was running funky during a regen and on my way home after that regen, I watched the soot percentage rise by 20% in 25 miles. I understand during DPF regen mpg drops but when I research out there, typical diesels are only seeing a couple mpg loss but that could be them talking about the average, not instantaneous. I have an appointment with dealership in a week to use their data logging tool, see what they report back with what a “normal” range should be. I’m getting normal operating values for all of the important parameters for this engine to monitor over time.

You’re correct, I am paranoid that I dropped $60K on a machine that I don’t have confidence in but maybe I am over thinking it a little. Plus, I’m an engineer and we all overthink everything so there’s that working against me too

TX_Critter · Sep 26, 2023

I’m an engineer too but I did a ridiculous amount of research before buying my truck since it was my first diesel so maybe I can help with some of your questions.

The LM2 / LZ0 was a clean sheet design in collaboration between GM and Opel and is one of the newest / most advanced diesel engines on the market. Since the turbo is on the small side and is variable geometry it is extremely responsive, from my personal observations boost only peaks for like one second at low gear / high RPM and moves around quite a bit. My impression is that the monitoring system is also quite a high sample rate so that also leads to the impression of variability.

These videos should give info about the engine better than I can:

Edit: One more thing about the MPG; I have noticed it can be a little variable outside of regen as well but have mostly chalked that up to the extra fuel burn on startup / warmup they talk about in the videos. I have personally noticed the truck gets pretty terrible mileage for the first 10 - 15 miles of a trip but then settles in and improves substantially. My highway mileage (stock AT4 ride height with a bed cover) is excellent after warmup at around 22 - 24 MPG but city mileage for short trips is not great, something like 16 - 19 MPG.

Dudeguyman · Sep 28, 2023

TX_Critter said:
I’m an engineer too but I did a ridiculous amount of research before buying my truck since it was my first diesel so maybe I can help with some of your questions.

The LM2 / LZ0 was a clean sheet design in collaboration between GM and Opel and is one of the newest / most advanced diesel engines on the market. Since the turbo is on the small side and is variable geometry it is extremely responsive, from my personal observations boost only peaks for like one second at low gear / high RPM and moves around quite a bit. My impression is that the monitoring system is also quite a high sample rate so that also leads to the impression of variability.

These videos should give info about the engine better than I can:

Edit: One more thing about the MPG; I have noticed it can be a little variable outside of regen as well but have mostly chalked that up to the extra fuel burn on startup / warmup they talk about in the videos. I have personally noticed the truck gets pretty terrible mileage for the first 10 - 15 miles of a trip but then settles in and improves substantially. My highway mileage (stock AT4 ride height with a bed cover) is excellent after warmup at around 22 - 24 MPG but city mileage for short trips is not great, something like 16 - 19 MPG.

More you post replies, more I’m with you on I am overthinking it haha.

Update: Now my MPG is fantastic but at the same time parking sensor is permanently disabled with no fuses blew - got in my truck today after a week trip and these two things happened. Has to be some electrical issue going on.

The boost situation still has me skeptical because it is low by 10 psi on its max but I do agree with you, it’s all over the place. During regen I’m seeing what you’re seeing but after regen drops by 10 psi again. I’m more concerned about the max psi but I’m also getting good performance now so non-issue I guess

. Thanks for the assist!

TX_Critter · Sep 28, 2023

Yeah I’ve noticed inconsistencies that I can’t explain, always just chalk it up to the emissions is doing something and not telling me about it, if you didn’t know there are two (at least) different types of regens…. One full on active regen that shows on iDash and another more passive one that you really have no idea when it is happening.

You’re on your own with the parking sensors, mine weren’t even hooked up for the first 11 months or so since I didn’t get that chip from the factory.

Dudeguyman · Oct 5, 2023

TX_Critter said:
Yeah I’ve noticed inconsistencies that I can’t explain, always just chalk it up to the emissions is doing something and not telling me about it, if you didn’t know there are two (at least) different types of regens…. One full on active regen that shows on iDash and another more passive one that you really have no idea when it is happening.

You’re on your own with the parking sensors, mine weren’t even hooked up for the first 11 months or so since I didn’t get that chip from the factory.

Quick update, NOx sensor 1 had to get replaced or at least that’s the dealers solution, for now. During data logging I noticed values that just didn’t make sense, brought it in yesterday and yup needs to get replaced. No CEL, no diagnostic codes, strange…sensor is on back order but fixing this might fix my mpg issue, hopefully but would make sense. I also found a couple wires showing bare copper with nothing even close to be caused by abrasion so must’ve come from the factory like that. Sucks to find all this stuff on my own. GM put out a technical service bulletin on electrical harness abrasion, plan on building up the problem areas they mention. I’m in RI and the roads are extremely bumpy so kind of not surprised. Crossing my fingers I have a good truck in the next week or so!