View Full Version : Running Rich??

24-11-2003, 09:45 AM
Hi, i've been told that my car is running rich (from a friend who was following me and noticed a black puff of smoke when i hit vtec).

Just wondering if its good/bad, and whether i should do anything about it.

I've been told that its excess fuel going to the engine etc, but noone has told me whether i should do anything about it or not.



24-11-2003, 10:55 AM
All honda's come from the factory rich, they run rich so it can prolong the life of the engine. Itz nothing to worry about at all, just remember running rich is better than running lean. If you really want to get rid of this problem, purchase a piggy back and adjust the A/F Ratio to lean it out a bit (via Dyno of course). It will increase your performance slightly and improve your fuel consumption too. All another way is to reset your ECU, see if that helps as well, as it will refer back to the stock maps.

24-11-2003, 11:39 AM
My car is the opposite and its running really lean. What causes it? could it be the mods?

[[d a n n y]]
24-11-2003, 11:54 AM
running rich is betta than running lean

24-11-2003, 12:37 PM
might pay to bring it to a place like unigroup and get a few power runs on the dyno to get some AFR readings.
I think they charge $55 for 3 power runs.

24-11-2003, 12:56 PM
Yeah my crx does that, used to worry about it a bit until i was chasing a couple of other gen 3's and realised they all did the same thing.

I assume intake/exhaust overlap doesn't help ?


24-11-2003, 01:20 PM
Rich is better for the engine, it keeps the engine cooler by throwing excessive fuel for combustion.

Saying that though imagine lighting a match stick and throw a bucket of petrol over it, will it ignite? ( for arguements sake lets say no ).

Too much petrol for the light to burn, this is what is happening in your engine on a much much much smaller scale but basically too much petrol for the sparks to burn optimum, the result is a lack of power from the engine and a higher fuel consumption.
Thats the only real drawback of running rich, lose power and uses more petrol and also you'll get that black sludge above your exhaust tip as unburnt fuel is pushed through the exhaust.

Bearing the above in mind, the leaner your car is running the more power its producing, however there is a high risk that you will lean out and melt a piston or two and basically cook the engine.

This is why cars from factory runs rich and never lean since they dont wanna have engine warranties issues from lack of fuel.

People who are into performance mods gets a piggy back controller like the Apexi SAFC II which controls also the air to the mixture for optimum power. Your tuner should have some experience and should be able to tune your piggyback computer for maximum power with a safety buffer not to lean out at any particular rev range.

The causes of cars running lean is usually to do with the air intake setup, if your car is stock then your air flow meter could be dying and needs replacing.

Say if you got a badly designed ram pod filter, when the car sucks air into the filter the air inside the filter could be travelling in all sorts of patters, from swirling to bouncing back and forth around the pod piping, usually its when the case of when air is travelling in a swirling manner. The problem is as it swirling like in a shape of a tornado it may go past your air flow meter without swiping the sensor, the ECU detects that theres no air or not enough air coming through the filter and it calculates with the amount of air is available to mix with the fuel, a small amount of air is to be mixed with a small amount of petrol and thus your car is running lean.

It is usually the pod filters that causes the car to run lean.

On the other hand when your car is running rich its due to the aftermarket exhaust, more free flowing exhaust means air can be expelled faster out of the engine and thus more fuel is used to keep up with this.

If you put the stock air box in then it should run normal again, if you have already got a stock box then get your sensors checked out cause it could be feeding your ECU the wrong readings.

24-11-2003, 06:10 PM
your smoking tony ;) shouldn't be a problem - just get a saf-c to adjust ur a/f ratio if you are concerned, will give you some gains as well :D

24-11-2003, 08:52 PM
I wouldn't sweat it too much, unless your consumption is out of whack.

People have already pointed out the pros to it and the mods that can be done.

I don't know if it makes much difference, but it costs nothing to reset the ECU after changing plugs, rotor and dizzy cap (if cracked or scarred inside), fuel filter and air filter. Pull the fuse and leave it out for 10 minutes. Replace it. Let the car idle and then shut it down when warm. Restart and go for a calm drive using as much as the rev range as you can.

Like I said, chances are it will make no difference, but I find mine runs better after doing this after 20,000 kms.

That or it's just in my head ;)

24-11-2003, 08:54 PM
lol don't forget tony's car is stock...he might've changed the filter (not sure) but defnitely not exhaust

24-11-2003, 09:07 PM
Your all forgetting the main point here, the reason your ecu seems to be running rich is because of the long term O2 / short term auto adjustment on every honda ecu, which is they reason why piggy back devices become invisable aftertime.

The air/fuel mixture is expressed either as the ratio of air to fuel vapour or as a lambda value. The lambda value is derived from the stoichiometric air/fuel ratio, which is the chemically correct ratio of air to fuel for complete combustion to take place. The stoichiometric ratio is 14.7:1 when expressed as an air/fuel ratio, or 1 when expressed as a lambda value. A richer mixture will have a lower air/fuel ratio and lower lambda value. e.g. an air/fuel ratio of 12.5:1 equals a lambda value of 0.85, and is a typical value for a naturally aspirated engine under full load.

The ECU aims to keep the air/fuel ratio close to the stoichiometric air/fuel ratio in order for the catalytic converter to work at maximum efficiency. This air/fuel ratio also gives good fuel economy. Under increased engine load the optimum air/fuel ratio is richer than the stoichiometric air/fuel ratio in order to give maximum engine output and prevent engine damage.

An oxygen sensor produces an electric voltage from the different levels of oxygen present in the air and the exhaust gas. If the mixture is rich then the exhaust gas will contain very little oxygen. The oxygen sensor will therefore product a voltage output, which the ECU senses and determines that the fuel mixture is rich. Conversely if the fuel mixture is lean then the exhaust gas will contain higher levels of oxygen, which produces a lower voltage output. The normal range of the oxygen sensor output signal is about 0.2V to 1.2V It should be noted that most stock oxygen sensors are designed to be particularly sensitive around the stoichiometric air/fuel ratio.

In closed loop operation the ECU uses one or more oxygen sensors as a feedback loop in order to adjust the fuel mixture. This gives the name ‘closed loop’ from the closed feedback loop. The ECU won’t run in a closed feedback loop all the time, so ‘open loop’ is used to describe the operation of the ECU when the mixture is not being adjusted in this way (usually when the engine is cold or when running under high load).

In closed loop operation the ECU uses the oxygen sensor to tell if the fuel mixture is rich or lean. However, due to the characteristics of the oxygen sensor it can’t tell exactly how rich or lean, it only knows that the mixture is richer or leaner than optimum. The ECU will enrich the mixture if the oxygen sensor shows that the mixture is lean, and lean the mixture if it looks rich. The result of this is that the mixture will swing back and forward around the stoichiometric point.

The ECU uses the short term adjustment to alter the injector duration, and therefore the mixture, in order to make the oxygen sensor voltage swing around 0.6V.


In the above picture where a short term mixture adjustment of approximately +-5% is used to keep the oxygen sensor voltage swinging about 0.6V The vertical lines on the graph are 1 second apart. The above graph was measured at idle. At higher engine speeds and loads the oxygen sensor voltage will pass 0.6V up to 20 times per second.

Over time the ECU will look at the average short term oxygen sensor adjustment and determine if the engine is running rich or lean overall. The ECU will alter the long term oxygen sensor adjustment based on the average value of the short term oxygen sensor adjustment. This has the effect of compensating for differences in each individual engine and other factors such as environmental conditions in order for the engine to run at the correct air/fuel ratios. There is a limit on the amount of adjustment of approximately +-30%


In the above picture the short term oxygen sensor adjustment shows that the ECU is on average leaning the mixture out by about 15%. Because of this the long term adjustment value is slowly being reduced to lean out the mixture.

It is best to disable closed loop operation while tuning. Otherwise what commonly occurs is that the ECU will alter the mixture using the long term adjustment while the car is idling between dyno runs, which means that the mixture is not repeatable between dyno runs.

If changes are made to the engine which alter the amount of fuel that is delivered (bigger injectors, increased fuel pressure or altering the air temperature sensor voltage) the ECU will compensate the best it can using the long term adjustment. Under high load when the ECU stops running in closed loop the long term adjustment is still used so increasing fuel delivery via these means in not recommended unless the ECU is recalibrated or closed loop disabled.

At part load it is best if the ECU is tuned so that the mixture is close to stoichiometric. This reduces the amount of time the ECU will take to use the short term adjustment to alter the mixture to get the oxygen sensor voltage to swing past 0.6V, and keeps the long term adjustment from the zero position.

Early VTEC engines use two oxygen sensors arranged to read one cylinder pair per oxygen sensor. The mixture for each cylinder pair is tuned separately. It is important not to wire the sensors around the wrong way, otherwise one cylinder pair will run lean, and the other pair rich. It is also important not to wire one oxygen sensor into both sensor inputs, otherwise the engine will run either very lean or very rich.

OBD II engines use one oxygen sensor before the catalytic converter, and one oxygen sensor after the catalytic converter. The function of the second oxygen sensor is to determine if the catalytic converter is functioning. It does this by looking at the difference between the two oxygen sensors. If the catalytic converter is functioning correctly there will be a reduction in the exhaust oxygen content as carbon monoxide and carbon dioxide is catalysed in the converter.

Regards James

25-11-2003, 07:34 AM
good info :)

25-11-2003, 09:59 PM
James - TY for the info on the O2 sensors - I was wondering why the EF8/9/XSi ran them :)

When I do my exhaust I'll be keeping the original header but will make sure they don't mess with the sensor wires.