mark kibort

is there a way to fake out the tempII or any other sensor to lean the car Way way out?? i mean , to the point where it can start missing?

If so, we could make a **** where you turn it full lean during part throttle hyway operation, and maybe make it go open loop as well by interupting the O2 circuit.

I know you could do this with the shark tuner, but since hyway cruse is where we need the benifits and it can be very crude as far as mixture goes, if we can lean the car way out , say to 17:1 we might end up at 30mpg on a 70mph hyway run.

so the question is, what resistor circuits can we mess with to lean the car out.
and are those circuits ignored during closed loop operation . ( WOT, and cold start periods)

Cheburator

If you have a cat car (closed loop) all you need to do is unplug the lambda sensor from the car's harness and then start the engine. The LH defaults to a safe lean map, which would get you 25mpg at 130km/h. When you plug it back and restart the car, you go back to your default closed loop maps. Tried and tested on my racer.

kelanel

would this work on l-jet cars as well? interupting the sensor wire with a safety switch seems easy enough. would definitely like the mpg boost!

Tom. M

I think Colin did this on his Megasquirted 928 a few years back... I think he got like 35mpg on a trip over to Spokane... but this again was with Megasquirt...where it was easy to change the A/F ratio in whatever range you wanted..

danglerb

This is one I will happily sit back and watch somebody else test.

123quattro

Moving from 14.7:1 -> 17:1 you are leaning out the mixture by about 15%. My car gets 20mpg on the highway. 15% better is 23mpg. Leaning it out also decreases torque some so you'll need less throttling to make the same power. Your throttling losses will go down some. Best case I'd say that gets you to 25mpg. Running lean will also cause the catalyst to not work. And if you go so lean as to cause misfire you may melt the catalyst if done for more than a few seconds.

Ethre

Might be able to do it with something like this.
http://www.jaycar.com.au/productView...T&SUBCATID=933

You would have to put the car in open loop, but by plugging it inline with your AFM I would think you could adjust the signal to shift your ratio any way you wanted.

John Speake

There's not a lot you can do when running closed loop. If you tried to make temp too too high a resistance to go lean and get to the limit of loop control range the loop will just revert to mid range.

The best way is to put a switch on the code plug to select cat (normal) or non cat (open loop that you can mess with to your heart's content. When on non-cat you can certainlt vary temp 2 to a higher resistance to go leaner.

KenRudd

Crappy gas mileage is a feature on a 928, not an issue.
Besides, at some point, somebody likely paid a gas guzzler tax on my car, and I feel I would be cheating them if it didn't guzzle that gas.

jcorenman

This is really simple with a Sharktuner, but you need to be running open-loop otherwise you are fighting the NBO2 sensor. We wired a switch to the coding plug as John said, to select the no-cat map (which also forces open-loop mode, even with the NBO2 sensor connected).

Then go into the no-cat fuel map, and lean out the block of cells in the highway-cruise part of the map, where ST's cursor hangs out on the highway. Then as you roll on the throttle for a grade, or for passing, you move out of that area map and back to normal fueling. I think doing it that way is safe, because you are never under much load when running lean. And I think you also want to add some ignition advance for best efficiency, because leaner mixtures burn more slowly.

I did some fiddling with this last year, but was never able to get more than a couple of extra mpg with mixtures around 17:1. That was average over a tank, but also I-5 through Oregon with grades and curves and stuff.

Maybe the best way to do this is on a long flat road, copilot driving with cruise control maintaining steady speed. Then monitor the mpg readout on a digidash while tweaking fuel and timing. (Or log injector-pulsewidth with ST, then take an average over a minute or so, and make small changes trying to minimize pulsewidth). Sounds like a good project for our next trip to Kansas.

And like Mike said, I was never completely comfortable running lean with my own car, even with ST and WBO2 running.

IcemanG17

MK
I don't think this would work....since the LH is reading the O2 at cruise TPS......unless you can change cruise O2 reading to 17.0....it won't work

However it WILL work just fine on my SDS system.....well if I had an 02 sensor and it setup that way....but in theory I could do it quite easily.....

SeanR

Wouldn't that be good up to the point you decided to pass that semi going 58 in a 60. Pedal down, boom engine?

Hold On

Sorry to say, that of my three vehicles, the 928 gets the best economy. lol How sad is that ? I think I will leave it alone.

scarceller

Leaning out fuel can improve MPG but the real trick is to properly tune ignition in the Part Throttle Ignition tables of the DME. The idea is to get the car on a load dyno and fine tune the cells that are used for cruise speeds, tune for max torque with AFR=14.7 and you'll have your very best MPG. Just leaning out fuel does not cut it because it can reduce torque. The bottom line is to generate the most torque possible with the least amount of air for the given unit of work. Where the unit of work can be defined as pushing the car along at say 60MPH. You simply want to achieve the given unit of work with the least amount of intake air which also coincides with peak torque with that unit of air. That's the science if your really serious about MPG.

Stromius

Won't leaning out the mixture cause overheating to the pistons? Maybe I'm thinking too much about motorcycles and airplanes. YMMV