Best mileage during dpf regen?

[PeterA1]

So in the past few months, I've taken my A6 TDI on quite a few 500+ mile drives and recently my mileage has been about 25% lower than what I used to be getting. I have tried everything in the tips for better mileage and those do help just a little bit, but I would like my old mileage back. For example, on a flat and straight road with no wind, I will get about 29 to 32 mpg, cruse control on 75 or 80 mph on my local 150 mile straight and flat stretch, both ways. The instant mpg meter wouldn't even touch the 40mpg tick mark. Here's the interesting bit - if my car starts doing a regen, the mileage shoots up to 40-50 mpg for the duration of the regen! My average mileage would increase significantly as well. It's the mileage that I would usually see about a year ago when I first bought the car. Obd11 shows no trouble codes with my car, and my dealer says I must have one for them to do any warranty work on it, otherwise I'll have to pay a $300 diagnostic fee if they can't find anything physically broken. I have less than 10k miles left on my dieselgate warranty which means it will be over by fall of '22 at my rate. Has anyone had this problem before, or know of a way to force a check engine light for the DPF? The only red flag I've seen in obd11 is that my car averages 296 miles between each regen.

 

[DivineChaos]

So in the past few months, I've taken my A6 TDI on quite a few 500+ mile drives and recently my mileage has been about 25% lower than what I used to be getting. I have tried everything in the tips for better mileage and those do help just a little bit, but I would like my old mileage back. For example, on a flat and straight road with no wind, I will get about 29 to 32 mpg, cruse control on 75 or 80 mph on my local 150 mile straight and flat stretch, both ways. The instant mpg meter wouldn't even touch the 40mpg tick mark. Here's the interesting bit - if my car starts doing a regen, the mileage shoots up to 40-50 mpg for the duration of the regen! My average mileage would increase significantly as well. It's the mileage that I would usually see about a year ago when I first bought the car. Obd11 shows no trouble codes with my car, and my dealer says I must have one for them to do any warranty work on it, otherwise I'll have to pay a $300 diagnostic fee if they can't find anything physically broken. I have less than 10k miles left on my dieselgate warranty which means it will be over by fall of '22 at my rate. Has anyone had this problem before, or know of a way to force a check engine light for the DPF? The only red flag I've seen in obd11 is that my car averages 296 miles between each regen.

Well winter fuel has worse mileage. What's your ash load?

 

[PeterA1]

Ash has been steady at 0.07L since I got the car a year ago. I've been able to try out different diesels, currently has a tank full of #2 and I get about 2mpg drop when I use Idaho's #1 and #2 blend and 2 more mpg when using pure #1 from Montana. The mileage has been down since August of 21, so I think I have ruled out the winter blend. I've also tried liqui moly lm2002 super diesel additive and noticed no difference. I have also tried being really easy on it as well as beating the snot out of it on some backroads. The only thing that I'm thinking would make a difference would be to remove the DPF and EGR and possibly a hybrid turbo. That will eventually happen, but I'd like to keep the warranty as long as I can.

 

[PeterA1]

I just wanted to give an update to this - it turned out to be a failing dpf and faulty pressure sensors. I'm glad to be back at a solid 37 to 38 mpg around 80mph on not very flat roads and over 40 if I try my best. I was also down on power too but I didn't notice the gradual decrease over time.

 

[sbmellen]

Well winter fuel has worse mileage. What's your ash load?

I don't think that Arizona ever switches to a winter blend. I can understand for the northern US and Canadia, but not here in Phoenix. Also, how is ash load checked?

 

[gforce1108]

I don't think that Arizona ever switches to a winter blend. I can understand for the northern US and Canadia, but not here in Phoenix. Also, how is ash load checked?

VCDS can show you: http://wiki.ross-tech.com/wiki/index.php/Diesel_Particle_Filter_Emergency_Regeneration

It mentions soot load in this procedure but there are quite a few other measuring blocks you can monitor.

 

[gforce1108]

better info here: https://forums.tdiclub.com/index.php?threads/dpf-stats-discussion.520749/

 

[sbmellen]

VCDS can show you: http://wiki.ross-tech.com/wiki/index.php/Diesel_Particle_Filter_Emergency_Regeneration

That's why I didn't know; I don't have a scan tool or a PC laptop!

 

[DivineChaos]

I don't think that Arizona ever switches to a winter blend. I can understand for the northern US and Canadia, but not here in Phoenix. Also, how is ash load checked?

There's portions of az that get cold.

 

[sbmellen]

There's portions of az that get cold.

Not enough for blend. If you can find proof that Flagstaff, Payson, Springerville get blended diesel from their tank farm (only two in AZ, west Phoenix and Tucson), then I'll eat my own shorts.

 

[DivineChaos]

Not enough for blend. If you can find proof that Flagstaff, Payson, Springerville get blended diesel from their tank farm (only two in AZ, west Phoenix and Tucson), then I'll eat my own shorts.

Only has to hit 20 for it to be an issue. Duncan, Wilcox, San Simon. There's more than a few. That's what froze last year. Better to be safe, than stranded.

 

[sbmellen]

Well, while I'm from Cochise County, I've lived in PHX since 1993. The coldest its been in the past 20 years was 29º. That's probably why I didn't know. My dad used to have a block heater on his 6.2 liter GMC diesel engine in the 1980s.

 

[DivineChaos]

Well, while I'm from Cochise County, I've lived in PHX since 1993. The coldest its been in the past 20 years was 29º. That's probably why I didn't know. My dad used to have a block heater on his 6.2 liter GMC diesel engine in the 1980s.

Better to be safe than sorry. During our coldest months. It can hit -50f air temp

 

[gforce1108]

That's why I didn't know; I don't have a scan tool or a PC laptop!

If you are going to be tinkering on your Q5 - you should buy VCDS. For $199 it can't be beat. OBDeleven is a cheaper, less user friendly alternative with some weird points system, but it'll do the trick if you don't have something windows based to run vcds. I keep a cheap laptop in the garage for my Elsawin virtual machine and VCDS.