Do 135i typically run rich?

[Seaice]

In the half-year that I've owned my 135i, it has been running rich. The tailpipe gets sooted-up quickly, and I can smell the gas, particularly before its warmed-up. No smoke, ever.

I replaced the VANOS solenoids (which threw the typical codes) and the spark plugs shortly after buying the car and since then, it has run perfect. There have been no more codes, I average 17.5 mpg in mostly heavy-footed city traffic, and I always run Chevron premium.

Is it typical for 135s to run rich?

[iminhell1]

I would check for boost leaks personally. 17mpg sounds low to me.
I'm on E50 and still manage 20mpg average.

[Matticus91]

Originally Posted by Seaice

In the half-year that I've owned my 135i, it has been running rich. The tailpipe gets sooted-up quickly, and I can smell the gas, particularly before its warmed-up. No smoke, ever.

I replaced the VANOS solenoids (which threw the typical codes) and the spark plugs shortly after buying the car and since then, it has run perfect. There have been no more codes, I average 17.5 mpg in mostly heavy-footed city traffic, and I always run Chevron premium.

Is it typical for 135s to run rich?

17mpg for a heavy-footed city driver is not bad. I'm currently averaging around 15mpg driving mostly city in DC area and then driving hard on the highways when I have the chance.

Oh and to compare gas I always run top-tier 93.

[Seaice]

Originally Posted by Matticus91

17mpg for a heavy-footed city driver is not bad. I'm currently averaging around 15mpg driving mostly city in DC area and then driving hard on the highways when I have the chance.

Oh and to compare gas I always run top-tier 93.

Chevron around here is 92 octane.

I don't think my mileage is too bad considering my driving habits and the car does run great, so I have not been too concerned except I'd like it to run leaner. Plugs looked good when I changed them, so I guess it's normal. But I will try to check all my vacuum lines.

Thanks

[The Wind Breezes]

The car fires the injectors twice per cycle on cold startup LIKE EVERY OTHER DI ENGINE to get the cat plenty of fuel so it heats up fast, duh.

The car also runs rich under power like EVERY OTHER street going combustion engine. If you're not asking for much power then the car will run as close to stoich as it can get for fuel economy and emissions.

[ShocknAwe]

The answer is yes. It runs rich. Perfectly fine. If you want to lean it out a bit tune it to do so. Cold start is super rich. Afaik FI engines typically run rich as well.

[tuj]

Actually, on decel, most ECU's are programed to do decel fuel cut-off at speed, resulting in lean conditions. And yes, almost all factory engines are programmed to run overly rich to protect the engine under high load.

I get about 19-20mpg very consistently. I'm light-footed on the way to work, but I hammer it home and at the track. The car see's at least 5k revs a few times on a daily basis after warmed up.

Running rich on a boosted engine also helps managed combustion chamber temps. The extra fuel can reduce the EGT.

[Seaice]

Thanks all.

To my recollection, all the modern cars (w/computers/ECUs) I've had have been designed to be lean-running.

[tuj]

Originally Posted by Seaice

To my recollection, all the modern cars (w/computers/ECUs) I've had have been designed to be lean-running.

This is true under certain conditions. Low-load, idle, the car will try to target the ideal EGT for the catalyst. This is usually a fairly high EGT. Some cars will also have an initial mode where for the first few minutes they run a higher idle to warm up the cat.

All my ex-cars (3xNA Miata, NC Miata, RX-8) ran rich under load. The RX-8 ran ridiculously rich, namely because if you get knock in a rotary, you are likely to blow the engine's apex seals.

But if you think about it, running rich is a way to preserve the engine under load. Therefore the factory tunes are conservative, and leaning out the fuel tables slightly can result in increased power (if done safely).

This is getting OT, but there was a hack on the NA Miata where you could replace the timing crystal in the ECU with one about 8% faster. This had the effect of raising the rev limiter about 500rpm and also changed the injector duty cycle, having the net effect of leaning the mixture slightly.

[Matticus91]

Originally Posted by tuj

...
But if you think about it, running rich is a way to preserve the engine under load. Therefore the factory tunes are conservative, and leaning out the fuel tables slightly can result in increased power (if done safely).

This is what I was about to say, and I tend to stay on the safe side with things like this. Unless you're a bigtime racer or a tuning pro I wouldn't really recommend trying to lean the car out too much.

EDIT:

Plus, running rich yields more fun noises

[elzorro4]

I always get into these kind of discussions... I say that my brake pads last 15k miles and everybody says somethings wrong, I have a 18mpg and someone says my fuel tank is leaking....
Although I think a lot of people know a lot and make accurate comments I think these kind of cars can vary a lot from user to user.
These engines have turbo and are 3.0L... if you drive them smoothly on the highway you can have a very good mpg, brakes and tyres would last as much as a Jetta.
But if you live in the city, with lights, traffic and/or want to go fast it will eat you alive... You have no less than 300hp on a 3L turbo engine drinking fuel and killing your tyres... and then you have to stop, killing your brakes....

IMO: 17mpg is OK with traffic/start stops.

[The Wind Breezes]

Originally Posted by Seaice

all the modern cars (w/computers/ECUs) I've had have been designed to be lean-running.

I doubt that unless all your modern cars have been a few specific models of Japanese economy cars that are 10 - 20 years old.

Originally Posted by tuj

This is true under certain conditions.

No, it usually never was, and it's definitely not now.

Modern ECUs will NEVER EVER target a mixture leaner than stoichiometric due to emissions. It's simple, lean burn won't produce acceptable emissions with a standard catalytic converter. Honda and some other manufacturers made some models that run lean under light load, but they haven't been made for over 10 years. Chrysler had one too it stopped being made over 20 years ago.

This whole thing is unfortunate because you do get better economy running lean under light load. I've experimented with this a little bit on MED9.1 which will allow you to request lean mixtures. Direct injection engines can get really good economy with a special leanburn mode since the local combustion can be stoich for great efficiency. This is different than just remapping the fueling, you have to have the engine change several other maps on low load like when the fuel is injected. Unfortunately this still produces the aforementioned emissions so they don't operate this way.

[tuj]

Originally Posted by The Wind Breezes

Modern ECUs will NEVER EVER target a mixture leaner than stoichiometric due to emissions.

I disagree.

To reduce CO emissions efficiently use of more fuel-efficient engines, such as lean-burn engines, which potentially offer greater fuel efficiency, may gain importance. Operating an engine with lean-of-stoichiometric mixtures (A/F ratios of 16:1 – 25:1) requires burning of fuel in an excess of oxygen and this can provide fuel consumption improvements of at least 10%, in addition to substantial reductions in CO and NOx emissions. Since a lean-burn engine operates close to the limits of combustion, its efficient functioning demands good mixture preparation, a very high energy spark to ignite the weak mixture and very good monitoring of combustion quality and mixture strength through a closed-loop control system. Many of these concepts are incorporated into recent Japanese designed engines, namely Honda’s VTEC-E and Toyota’s Carina-E. These engines can typically run at A/F ratios of 22:1, meet European and US emission regulations and offer fuel consumption improvements of up to 25% under cruising conditions.
The most important component of their control systems is a type of EGO sensor (called a universal exhaust gas oxygen sensor or UEGO sensor), which delivers a variable output current in proportion to exhaust oxygen content.
18.6.1.

DECELERATION LEANOUT
When the engine is decelerating, such as what would occur when the car is at city driving speeds and you let off the gas, a leaner air/fuel mixture is required in order to reduce the emission of excess hydrocarbons (HC) and carbon monoxide (CO). The ECM looks at MAP and TP (or MAF and TP) sensors to determine when to enter the deceleration leanout event, the amount of leanout required, as well as how long to stay in decel leanout mode. If this mode wasn’t operating, not only would there be an increase in emissions, but you could also get a backfiring in the exhaust due to excess fuel buildup (HC’s).

DECELERATION FUEL CUT-OFF
During conditions of extreme deceleration, such as what would happen if you let off the gas when the vehicle is traveling at highway speeds, a complete fuel cut-off of the engine can be commanded by the ECM to cut all emissions output. This also has the benefits of allowing the engine’s compression to slow down the vehicle (called engine compression braking). The ECM looks at MAP or MAF, TP, and vehicle speed to determine when to enter decel fuel cut-off mode and how long to stay in this mode. This mode overrides decel leanout mode. Instructions in the ECM programming determine when this mode is to be exited to prevent engine stalling.

[The Wind Breezes]

Originally Posted by tuj

I disagree.

Silly Puerto Rican, you didn't read my post! I already covered those Hondas and they haven't been made for 10 years, the other cars even longer. Try again.

[tuj]

Originally Posted by The Wind Breezes

Silly Puerto Rican, you didn't read my post! I already covered those Hondas and they haven't been made for 10 years, the other cars even longer. Try again.

Are you saying lean deceleration fuel cutoff is non-existent today?

[The Wind Breezes]

Originally Posted by tuj

Are you saying lean deceleration fuel cutoff is non-existent today?

No, you're correct. I didn't read your post and some deceleration is an exception. You are now a wise Puerto Rican.

[Dackelone]

The only way to know If your engine is running rich is to use an OBDII scan tool and read the lambda values.

Perhaps your car has a vacuum leak and the ECU is trying to add more fuel. Or perhaps your O2 sensor(s) are bad. Does your car have a tune?

[Seaice]

No I don't have a tune.

Certainly could be a vacuum leak... Car has 85K on it, but it runs so good I don't feel like running that down. I do have a slight valve cover gasket leak and it seems that can cause vacuum issues.