Sigh... just can't catch a break with this thing. Swapped injectors and ecu is telling me it's dumping fuel. Thinking I'm going to have to swap to the old injectors because I need to make a 3 hour road trip in 2 hours.

 

For what's worth. My 05 R53 seldom get better than 26-27 mph from day 1. I drive about 60% city and 40% highway, and I am not the kind with digital right foot. R52/3 are never a miser on petrol economy. From what I understand, close loop fuel trim is optimized for emission and not at all fuel economy.

When people comment that little car must be great on fuel, I try to withhold my honest comment as they think I am pulling their legs.

 

At least I confirmed that my original injectors are indeed 330's. I guess I could've pulled them and saved myself $50 for the new set. Oh well. It'll be worth it to send them out and not have any down time.

Current plan is to send these "new" injectors out and have them cleaned and flowed professionally and then I'll swap them in again and then I know I'll have fresh 100% functioning injectors.

Beyond that I'm at a loss as to why I'm still running so rich - especially since it has a Sprintex on it. By all rights, I should be lean. I shouldn't be at the edge of too rich. Does it just need to be tuned?

 

Also supercharger is very inefficient. I read that the SC takes tens of HP to spin at high boost. Unfortunately very little useful information on the web on their efficiency, as it is a very complex function.

 

what fuel trims do you have?

 

Same.

When I got my stock 2002 MCS back in 2008, it got around 28 MPG.

Ditching the OEM Dunlop run flats was a noticeable hit. Those tires ran really hard but the rolling resistance must have been low.

Now with around 90K miles and a 15% SC pulley I get the typical 26 MPG with a similar city/highway mix. Also get some soot on the tailpipes.

Recently replaced the front O2 sensor with an NTK - made NO improvement.

 

It's going to sound incredible. I don't know. I have not bother to hook up an ODB equipment. All I know is my spark plugs reads just fine. I also realized that you cannot judge the mixture rich/lean by the soot at the tailpipes. It is because it is post-cat.

I have not loook into fuel trim parameters from the ODB. All I know is there is short term, long term, and open loop. Close loop fuel trim is not constant but a sawtooth wave. For this I would be very careful in interpret what the number from ODB says.

I am getting a A/F meter, but my interest is more in the WOT open loop A/F ratio driving flat out on track. My main concerns are melting the cat or melting the valves.

On driving on public roads, if you are getting near my MPG, I would not waste time chasing for better MPG.

 

Yes a supercharger is less efficient than a turbo; it typically requires more maintenance as well. This is why it is not usually a good choice for the average passenger car. The beneficial trade-offs are less lag on boost and more linear boost production with RPM.

We really can't use turbo boosted engines as references for efficiency...

 

I should have make it more obvious the degree of inefficiency. It takes tens of HP to spin the lousy air compressor they call supercharger, and in exchange we get back tens of HP. It should be called tractor air compressor. Tens of HP of input - tens of HP of output give you very lousy efficiency. However for the sound, and lag of turbo lag, I will not trade my R53 for more efficient R56, even we have a cast iron boat anchor up front.

 

Here is one of many videox of closed loop fuel trim. It is not specifically BMW, but I think it applies to most cars with narrow band O2 sensors. Shocking that fuel trim is not optimized for fuel efficiency, but for emission, and the subject of emission is very complex not to mention how car companies have designed to game the regulatory emission laws. Yes, you can get better emission by compromising on MPG.