Poor fuel economy - 6L manual

[exanVZ]

50% adding in at times ? looks like its overly compensating for something maby bad 02 sensors, if u can look at the 02's millivolts see what those are doing, but mostly a stock tune would be within 5-15% error pos/neg and a tuner should have it within 5% so if ur 50% have to find out whats causing it

thanks for the input on this, it's a fairly conservative tune only about 350rwhp but maybe it needs a retune, I would just drop it into the workshop for a look but they are fully booked for the next few months and not sure I want to take it somewhere else or to different mechanic to look at, so trying to rule out anything else that I can by myself if I can. have tried to map out that data and look for a pattern but not seeing anything that makes sense to me, will have to do some more research on this over the weekend.

 

[07GTS]

tunes dont just change tho so something mechanical is causing it like sensor input or such, 50% is alot to be out, what does the LTFT say or are they disabled ?

 

[exanVZ]

tunes dont just change tho so something mechanical is causing it like sensor input or such, 50% is alot to be out, what does the LTFT say or are they disabled ?

I enabled logging for the LTFT on both banks but it's just reporting 0 so might be disabled, it's also a MAFless tune so that's reporting 0 too, and logging AFR it's just set to a constant value that never changes, constant 14.7.

I've tried to log everything useful into one big CSV file but it's just a bit hard to map things out and share them in an easy to read way. I could probably just dump the whole CSV if that would be useful to look at.

 

[07GTS]

yea the AFR will only change when u enter PE (close to or full throttle) or it should change, also should be lower for cold starts n such, yea if the LTFT are zero then its prob disabled, can be worth a shot on a csv file as it may be convertible to a hptuners scanner and be viewed, im not good with all the files n such but can give it a go

 

[exanVZ]

yea the AFR will only change when u enter PE (close to or full throttle) or it should change, also should be lower for cold starts n such, yea if the LTFT are zero then its prob disabled, can be worth a shot on a csv file as it may be convertible to a hptuners scanner and be viewed, im not good with all the files n such but can give it a go

torque log - Pastebin.com

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

pastebin.com

if you copy that to a notepad, save it as .csv then it should be importable into spreadsheets or maybe other log reading software
appreciate your help!

edit: have uploaded another log with a bit more data from my drive home from work, seeing the same kind of thing on this one, and from my analysis seems like when it's cruising at like 80k's 5th gear low rpm, that's when the STFT seems to like to go to ~+50%

GPS Time, Device Time, Longitude, Latitude,GPS Speed (Meters/second), Horizontal - Pastebin.com

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

pastebin.com

stuffing around a bit more with trying to log this data, found it pretty easy with power bi but hard to visualise so much data in a single screenshot or easy to share method. this seems to show that when getting little to no signal from the o2 sensor it's dumping in heaps of extra fuel, then when it gets a signal from o2 it cuts back to something more reasonable, assuming i'm understanding this correctly. still not sure if this means my o2 sensors are stuffed and aren't providing good reading, or something else weird is going on here.

 

[exanVZ]

managed to speak to the workshop about this yesterday, comparing bank 1 and bank 2, bank 2 looks a lot more normal so that kind of eliminates vacuum issues. grabbed 2 new o2 sensors to swap in and do some more testing after, if that doesn't sort it, they going to chuck it on the dyno for me and have a look at what's going on.

 

[07GTS]

yea i couldnt work out how to get the file to work on scanner, see how the 02s go, also was thinking as u got new exhaust if there are any leaks in it then that will cause issues also as the 02s will pickup on all that stuff esp upstream of them

 

[exanVZ]

yea i couldnt work out how to get the file to work on scanner, see how the 02s go, also was thinking as u got new exhaust if there are any leaks in it then that will cause issues also as the 02s will pickup on all that stuff esp upstream of them

Cheers mate, the pre cat o2 is actually in the end of the headers so don't think there's much room for a leak unless it's at the exhaust manifold and all seems good, hoping the new o2's do the trick, feel like I've been able to narrow it down and exclude a few things so confident I'm on the right track. really appreciate your advice, and everyone else who has had suggestions in this thread.

Also from my discussion with the workshop, they basically disable the post cat o2 in the tune so it's not feeding back any info and shouldn't impact this at all, which I didn't know before so good to know.

 

[exanVZ]

Swapped over both pre cat o2 sensors, bit of a pain as they are right at the end of the headers, not necessarily hard to reach but just not much room under there to work. I don't know what old O2 sensors are really meant to look like, but I think they are meant to look a bit like old spark plugs, these look pretty bad, has definitely been running super rich. I don't know if they might come good with a decent clean or something, not sure if it's worth keeping them for anything.



After that, reset my trip computer and went for a quick drive about for 10-15 mins. The car feels a little nicer to drive, and my fuel consumption has dropped from over 20L/100km (tested via computer and manual tracking) to about 12.8L/100km, it will be a bit worse than that in traffic but still a result I'm happy with for this engine. Also pulled some logs from the computer to see what the new o2 sensors were doing and how it's affecting the fuel trims and everything is looking much better here too.

 

[exanVZ]

After test drive last night, then driving to work and back home today in the usual traffic, fuel economy is sitting at about 13.4L / 100km, happy enough with that, that's about how much I think it should be using for city driving.