O2 Sensor - ECU Control

[MLM 57]

Hi Guys,

I have some mods i would like to do to my car which will potentially slightly alter air fuel ratios. Normally (i assume) this difference would be taken in to account by the ecu via the O2 sensor. Ie by sensing a rich/lean condition and adjust within its parameters.

Thing is i dont appear to have an O2 sensor. There is none in the exhaust, the plug under the car has a blanking cap and the relay is blank also.

Car is a '92 e36 318IS

So my questions are:

Is this correct. Did some e36 318is cars not have O2 sensors. If so does any one know why? (e30s have them right? therfore its a backward step in terms of ecu control)

Is it possible its previously modified with a O2 delete, again any ideas why?

If i dont have an O2 sensor how does the ecu know whats going on air fuel wise. Does it just run off a dumb map where TPS and MAF set fuel rates.

Any help or insight much appreciated

[*Glenn* 854]

Some did some didn't. Fuel is regulated by TPI, temp sensor, AFM, RPM and camshaft position sensors

What do you plan on doing ?? BTW: when youve done whatever your going to do, get Gavin @ High Velocity to remap it for you

Edited March 4, 2010 by *Glenn*

[MLM 57]

Awesome, Thanks Glenn.

This is whats happening http://www.bimmersport.co.nz/forums/index....showtopic=28044

The advice I have so far is to put the ITB's on with a standard map so it can be run on the dyno to determine correct runner length. By increasing length in 50mm increments for example I can see how the engine responds. This then allow me to design a plenum and runners to suit the engine. Theoretically I would need ~430mm runners to achive usable power. However there is nothing like real world testing.

While the itb's will be running with a standard map for this process the ecu should see a mass airflow at a certain rpm and temp and throttle position and allocate fuel and spark to match. However seeing as i have no O2 sensor it will will not correct itself if it is wrong.

At this point im just figuring a plan of attack.

Also this is only temporary for testing before a appropriate map is sorted.

[*Glenn* 854]

When you remap on the dyno you reset the parameters to correct fuel mixture by using a gas analyser at specific points. ie: load/revs

[CamB 48]

I'm pretty sure closed loop control is pretty crude compared to what you're imagining as well, on an ECU of that age.

Plus, it might see a different mass airflow for any given rpm and throttle setting, but unless the characteristics of the engine are significantly changed I would have thought the fuel requirement for any given airflow (which might be higher) was roughly the same, and that the spark requirement wouldn't be THAT different as you're not changing cam. So, speculating a little, it might be ok (and you should get it tuned anyway).

Does that make sense?

[*Glenn* 854]

I'm pretty sure closed loop control is pretty crude compared to what you're imagining as well, on an ECU of that age.

Plus, it might see a different mass airflow for any given rpm and throttle setting, but unless the characteristics of the engine are significantly changed I would have thought the fuel requirement for any given airflow (which might be higher) was roughly the same, and that the spark requirement wouldn't be THAT different as you're not changing cam. So, speculating a little, it might be ok (and you should get it tuned anyway).

Does that make sense?

+1.. I would agree with that as well

[MLM 57]

I'm pretty sure closed loop control is pretty crude compared to what you're imagining as well, on an ECU of that age.

Plus, it might see a different mass airflow for any given rpm and throttle setting, but unless the characteristics of the engine are significantly changed I would have thought the fuel requirement for any given airflow (which might be higher) was roughly the same, and that the spark requirement wouldn't be THAT different as you're not changing cam. So, speculating a little, it might be ok (and you should get it tuned anyway).

Does that make sense?

If i have understood you propperly. This is the theory I am running with so that I can run the engine to investigate runner length etc. I wont pick up any power until its tuned propperly. Ignoring the fact its ITB, from the ecu point of view it effectivly has an increased throttle diameter. Therefore for a given throttle position the mass air flow would (potentially) be greater, hopefully within the ecu's parameters. The engine should run safely if not at its optimum untill its tuned.

[CamB 48]

That's what I reckon - the ECU probably (yes, I am guessing but this is "normal" for an ECU) delivers fuel and spark based on airflow vs rpm. The throttle position is an input into extra fuel on pressing the accelerator (acceleration enrichment) and cutting it a little when its lifted (I think!). This is how most aftermarket ECUs work (although with a map sensor not mass flow).

So, assuming the airflow remains within the AFMs range, its hard to see how the fueling inputs will be much outside of what is expected by the ECU.

[MLM 57]

That's what I reckon - the ECU probably (yes, I am guessing but this is "normal" for an ECU) delivers fuel and spark based on airflow vs rpm. The throttle position is an input into extra fuel on pressing the accelerator (acceleration enrichment) and cutting it a little when its lifted (I think!). This is how most aftermarket ECUs work (although with a map sensor not mass flow).

So, assuming the airflow remains within the AFMs range, its hard to see how the fueling inputs will be much outside of what is expected by the ECU.

Thanks for your help guys, I will give this a go and see the results.

[*Glenn* 854]

The advice I have so far is to put the ITB's on with a standard map so it can be run on the dyno to determine correct runner length. By increasing length in 50mm increments for example I can see how the engine responds. This then allow me to design a plenum and runners to suit the engine. Theoretically I would need ~430mm runners to achive usable power. However there is nothing like real world testing.

You could make the runners with plastic tubes. Start at about 8" and have another tube that slides over the first tube with hose clips so you can quickly adjust the tube lengths to set incriments while on the dyno. This will take less dyno time.

BTW: You can also play around with cam timing on the M42 motor as well

Edited March 4, 2010 by *Glenn*

[MLM 57]

You could make the runners with plastic tubes. Start at about 8" and have another tube that slides over the first tube with hose clips so you can quickly adjust the tube lengths to set incriments while on the dyno. This will take less dyno time.

BTW: You can also play around with cam timing on the M42 motor as well

Thanks Glenn, The least time on the dyno the better for figuring these things out. The throttle body abd the plenum butt up against one another with a rubber sleeve joining the two with hose clamps. I had intended to take a number of set lengths for quick swap overs for which I could plot the results in excel and interpolate intermediate lengths. I do like the sliding arangement idea though would make infinately variable adjustments possible.

The factory adjustable cam gears are a bonus! When it comes to final setup and tune i may find a bit more power here.