Terrible fuel economy - possible injector issues?

[Scharbag]

I have a question about fuel economy and possible injector issues.

As you can see, my economy is pretty bad. I usually use 20-22 L/100KM (12-11 USMPG) when driving around town. Some highway driving in the past got me 12 L/100KM (20 USMPG).

I realize that I did not buy this car for efficiency That said, I also have an issue with pre-det while using a 91 octane tune and 91 octane fuel. This pre-det issue is really bad at WOT at low RPM and persists at WOT high RPM.

My plugs are 10,000 KM old (NGK - OEM). I have run SeaFoam through the fuel system as well as the spray through the intake. If I run 94 octane, I seem to have far less of an issue.

If I run the stock 241E ECU file, the pre-det issue seems to go away.

The car has never set any codes related to knock, fuel, spark etc.

Anyway, I have read that poor injector flow can cause all sorts of pre-det issues and possible fuel economy problems. Is this something I should consider investigating further? New injectors (BOSCH OEM) are not much more than getting mine tested.

Any help would be greatly appreciated.

Cheers,

And I even added a poll!!

[e90335e36m3]

I think this is completely normal, my combined MPG is usually around 16.5. If you drive your car remotely spiritedly, this is normal.

[SAMM3Y]

Fuel consumption is consistent to what I see. Are you tuned? Are you getting knock? As long as your lambda is consistent between the two banks i can't imagine all fuel injectors need replacing, what makes you think your pinking? Are you throwing codes? Can you hear it? I've only ever had one issue with a fuel injector in 20 years of Motorsport with a stuck open injector. I'd try changing gas stations or tune before I'd spend money on a set of injectors. Also I'd look for unmetered air leaks or change pre-cat o2 sensors.

[Scharbag]

Originally Posted by SAMM3Y

Fuel consumption is consistent to what I see. Are you tuned? Are you getting knock? As long as your lambda is consistent between the two banks i can't imagine all fuel injectors need replacing, what makes you think your pinking? Are you throwing codes? Can you hear it? I've only ever had one issue with a fuel injector in 20 years of Motorsport with a stuck open injector. I'd try changing gas stations or tune before I'd spend money on a set of injectors. Also I'd look for unmetered air leaks or change pre-cat o2 sensors.

I am tuned. Currently running Dinan tune. Seems good but I have been running 94 octane. I will try 91 on the next fill.

If this is the "normal" S65 fuel milage, then that is fine. It is horrendous, but that is likely due to it being hard not to drive it spiritedly...

And as far as the pre-det: I can hear it quite clearly. Given it is so obvious, I am confused as to why the ECU has never ever thrown a code. It has been better since I changed back to the Dinan tune from another tune. One item my car has is the larger Dinan throttle-bodies. Not sure if that would have any effect. As I said, stock program is fine. And I have also not had any injector issues in the past - and I have driven a lot of miles, both on the road and on the track. I just would love to get this all sorted. Looks like it is ~$35 per injector to have them cleaned and tested. Or about $60/injector for new BOSCH units. I would rather not have to spend the money though.

Thoughts on the larger throttle-bodies and their possible effects on a tune?

Thanks again for the help.

Cheers,

[SAMM3Y]

I think assuming your dinan tune is tailored to work with your larger throttle bodies I'd look for carbon buildup on your pre cat o2 sensors causing an issue. I've read on the forums before that they can cause a run lean scenario, I'd say try reaching out to dinan for support but heard they're pretty hopeless on retuning queries. I'd definitely make sure the plenum is nice and tight too with no air leaks... also I've I'd cross check that part number for injectors if you're gonna go that route. I've seen them for$25-$30/each advertised before. Good luck

[Redd]

I get 5km/L, so that's about 20L per 100km. Sounds about right for mainly city driving. Welcome to M3 ownership. 😂

I was getting around the same stock and with BPM Stage 2 tube. A CF driveshaft made it about 8-9% better, but that's about it.

[Scharbag]

Thank you all for the input. I will take a look at the O2 sensors as well. IIRC, these problems mostly started when I put my primary cats back in. Perhaps the shop that did the work damaged the O2 sensor(s) somehow.

Grasping at straws now...

Cheers,

[BayE30]

fuel economy sounds pretty normal to me... i get about 20mpg highway, and somewhere around 12mpg in the city. AVG MPG over the last 6k miles is 15mpg.

[Richbot]

Conservative highway driving, cruise set at 70-72mph actual road speed, nets 21mpg on my 117,000 mile '08 6MT

Go faster and it's worse

City driving and it's much worse

My 50/50 city/highway tanks are usually 16-17

If it's true city, 11-12 seems totally normal to me.

Sounds liek your tune is too aggressive for 91

[Scharbag]

Originally Posted by Richbot

Conservative highway driving, cruise set at 70-72mph actual road speed, nets 21mpg on my 117,000 mile '08 6MT

Go faster and it's worse

City driving and it's much worse

My 50/50 city/highway tanks are usually 16-17

If it's true city, 11-12 seems totally normal to me.

Sounds liek your tune is too aggressive for 91

One would think but the tune I am running is used by many without issues. I have been told by the tuner that my Dinan tune is WAAAAY more aggressive than the 91 octane tune he provided. I drove the car on the Dinan tune for about a month right after I bought it and before I put it away for the first winter and never had any knock. I used Shell 91 at that time every fill.

Then, I cut off the cats, put a Stage II tune in it and drove to California and back (7000km) and never had any issues. Once back, I did not like the smell after removing my cats. So I had a shop weld them back in and went to a Stage I tune from the new tuner. That is when I started having pre-det issues when running 91. I thought it may be bad gas. Tried 94 for a bit (Husky with Ethanol) and it was better. Now, if I run the 91 octane tune with 91 octane fuel, I get pre-det.

I will try 91 octane Shell instead of 94 octane Chevron on my next fill and see how the Dinan program reacts.

And again, thanks for all the fuel mileage info. City driving or spirited cruises is pretty much all I use the car for now. So I guess I can expect to go through the go juice!! Good thing Shell has Air Miles!!

Cheers,

[xander_g]

Fuel consumption seems to be within normal range. When was the last time you changed your spark plugs?

[Scharbag]

Originally Posted by xander_g

Fuel consumption seems to be within normal range. When was the last time you changed your spark plugs?

Car has 48,000KM on the ODO. Changed the plugs at 31,160KM. So they are pretty new. I took them out last fall and they all looked really quite good.

[Scharbag]

How in the hell do people get 14-16 L/100KM (~15MPG) in the city? With mixed highway and city use I barely get that!! My average since I bought the car is 17 L/100KM and that includes a 7,000KM road trip.

Or perhaps I just drive like a total douche...

Hmmm...

[Helmsman]

Scharbag I'm at 15.4L/100km average over the years, according to the gauge which we know lie about 0.1L/100km. Still not too bad.
Most miles are 8 miles commune i.e. fairly cold engine.
20-22L/100km seems very hight?

[Scharbag]

Originally Posted by Helmsman

Scharbag I'm at 15.4L/100km average over the years, according to the gauge which we know lie about 0.1L/100km. Still not too bad.
Most miles are 8 miles commune i.e. fairly cold engine.
20-22L/100km seems very hight?

Yes, it is painful to gas up as often as I do.

[Scharbag]

Originally Posted by SAMM3Y

I think assuming your dinan tune is tailored to work with your larger throttle bodies I'd look for carbon buildup on your pre cat o2 sensors causing an issue. I've read on the forums before that they can cause a run lean scenario, I'd say try reaching out to dinan for support but heard they're pretty hopeless on retuning queries. I'd definitely make sure the plenum is nice and tight too with no air leaks... also I've I'd cross check that part number for injectors if you're gonna go that route. I've seen them for$25-$30/each advertised before. Good luck

The price on the injectors was from Rock Auto and is in CAD. Welcome to Canada, please give us your money... Cleaning is about $30 each plus shipping etc.

Anyway, I do not really want to huck parts at this thing. What sort of logging should I look at to see if the front O2 sensors are behaving properly? Is there a chance that the O2 sensors were damaged when being removed/installed? I would think that this would just set a code. New O2 sensors are not terribly expensive but I would rather save the money to pay for fuel

Thanks again!

[MaximusB]

Could be bad gas? Have you tried filling up at a different station?

It is not unheard of in Lower Mainland/Vancouver Island. Few years back Chevron supplied a bunch of gas stations in Vancouver with 89 as 94 octane. Caused a huge headache as TONS of people had issue with their car. Lots of people showed up at the shop I normally go to thinking their tune was off and etc.

Also another interesting thing to note is US 91 octane is slightly different than Canadian 91 octane. The same shop did a test where they dyno'ed their skyline on 91 from the states, 91 local and 94 local gas. The US 91 octane was quite comparable to the 94 we have here. I didn't witness their test, they only told me about it when I asked them to tune my celica to 91 octane.

[Scharbag]

Originally Posted by MaximusB

Could be bad gas? Have you tried filling up at a different station?

It is not unheard of in Lower Mainland/Vancouver Island. Few years back Chevron supplied a bunch of gas stations in Vancouver with 89 as 94 octane. Caused a huge headache as TONS of people had issue with their car. Lots of people showed up at the shop I normally go to thinking their tune was off and etc.

Also another interesting thing to note is US 91 octane is slightly different than Canadian 91 octane. The same shop did a test where they dyno'ed their skyline on 91 from the states, 91 local and 94 local gas. The US 91 octane was quite comparable to the 94 we have here. I didn't witness their test, they only told me about it when I asked them to tune my celica to 91 octane.

I tried different stations in Saskatoon and now Victoria. I have been running Chevron 94 but I will try Shell 91 here on my next fill with the Dinan code. I may just pull my injectors and have them serviced as it is not terribly expensive and I have a spare car.

Thank you for the fuel information. I will get this sorted!!

Cheers,

[ItsGary]

Originally Posted by Scharbag

The price on the injectors was from Rock Auto and is in CAD. Welcome to Canada, please give us your money... Cleaning is about $30 each plus shipping etc.

Anyway, I do not really want to huck parts at this thing. What sort of logging should I look at to see if the front O2 sensors are behaving properly? Is there a chance that the O2 sensors were damaged when being removed/installed? I would think that this would just set a code. New O2 sensors are not terribly expensive but I would rather save the money to pay for fuel

Thanks again!

I've seen injectors on FCPEuro for $22usd/each but now they've gone back up in price to $50usd/each

[monterey]

new trottle actuators bumped my mpg from 10 to 12

[wfdeacon88]

I'm averaging 21.4 MPG mostly highway. On days when I'm driving more aggressive and less highway, I'm at ~17-18 on avg...

[Scharbag]

Recent mix of city and a 230KM round trip on the highway at reasonable speeds.

16.6 L/100...

This fill was a pretty full tank of Shell 91 and have driven it hard for a few drives. I am not getting the severe pre-det at full throttle and low RPM so that is a positive! I am really starting to think that the non-Dinan tune contributes somehow to the pre-det. I have no proof other than the Dinan tune does not pre-det.

Oh well, I am still likely going to have my injectors cleaned so that I can eliminate that variable from the equation.

Cheers,