Cleo has become an MPG project

[Philip1]

I tried the lean tune out today... Good thing I have several tunes to switch between. I had to go back to my base tune. I pulled too much fuel or didn't add enough timing. I had missing and shuttering till I switched back to the base tune.

[Philip1]

Ok I got a tune that works lots of ignition timing and pretty lean but it pulls better too.

[DRW]

Good progress! I also get misfires sometimes, I tune it so it's on the edge of misfires. Sometimes if the car is started when it's hot it'll misfire if I jump into lean burn mode too quickly, but that's rare. 99% of the time it runs nice with no signs of anything unusual except for a flatlined wideband gauge.

Gapping the spark plugs a little wider reduced misfires slightly on my car. It might be worth a try.

[Philip1]

I have my plugs gapped on the wider side of spec (.028-.032) at .034. I think my problem was I was not agressive enough with the timing.

[Philip1]

I just had an epiphany. If the oxygen sensor is on changes to the fuel map are negated. New plan tune a lean cruise open loop tune.

[SarkOzy]

A few thoughts.........

I'm not familiar with BMW systems, but you should look around and see if there is some sort of factory lean cruise subroutine already included in the ECM, just not turned on. Coming from the GM world we're very lucky in the fact that these modes are already programmed in, albeit not turned on due to EPA regulations concerning tailpipe emissions.

That being said, I think you're going about this incorrectly. De-fueling the engine to the point of sacrificing drivability isn't going to garner a substantial increase in economy. In OEM lean-cruise modes, it's only activated when a certain cruise parameter is set. By that I mean the engine is only lean at highway cruise speeds with very little load. If you spend a good deal of time at steady speeds then it's great.

You have the right idea by going open loop......the factory GM code is sort of a quasi-open loop mode that adds up to 50 degrees of SA while commanding anywhere from 16.2 to 16.7 AFR (get a wideband and tune in Lamda and you'll be better off) at cruise. It goes in and out of this mode to protect the catalytic converters. For me, the gain in economy is 20-30% in similar weather conditions. So it works.

I would GREATLY benefit you to get a wideband O2 sensor if you're going to be playing with the fueling. Stock narrowbands are great as long as you're right around stoich, anything else and they're junk. I'd really hate to see you blow a hole in a piston accelerating onto the highway because the engine is too lean.

[Philip1]

First the ecu is aftermarket the stock one has one program. Second I will not be blowing a hole in anything this computer has a separate map for acceleration. Next I am pulling fuel in just the light throttle cruise section about 1000rpm will be affected. I am adding timing across the board to improve economy slightly in regular modes I am not advancing it to detonation that would be stupid. As far as a wide band yes I will be getting one but for now I have been borrowing one when I tune.

[trollbait]

I'm not familiar with BMW systems, but you should look around and see if there is some sort of factory lean cruise subroutine already included in the ECM, just not turned on. Coming from the GM world we're very lucky in the fact that these modes are already programmed in, albeit not turned on due to EPA regulations concerning tailpipe emissions.

Going off topic, how do you find out if this routine exists, and how to turn it on?

[Philip1]

On your HHR you will need either a really agreeable dealer or hptuners.

[Philip1]

I have expanded the rpm range to lean out. I now have leaned out from 1800 to 2600 and up to 40% load. This will cover pretty much all cruise conditions. Switching between the stock tune and the modified tune while on level ground steady throttle and speed (60mph) I saw instant milage change by 7 mpg with no change in the feel of the car.

I have an ecu that allows instant switching between tunes.