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Idea: Tune power/econ AFRs by altering injector voltage? 


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 Post subject: Idea: Tune power/econ AFRs by altering injector voltage?
Posted: Sun Jan 13, 2013 5:06 am 
Parts Gopher
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Age: 42

Posts: 82

Joined: 24th Jun 2009

Ride: EF XR6

Location: Bendigo
VIC, Australia

Had an idea for realtime tuning of peak power or economy AFR, by controling the injector B+ rail voltage/current..

You could use a big transistor as a high-current variable resistor spliced into the positive voltage feed to the injectors to dynamically reduce the AFR. This wouldn't help with finding peak power rich mixtures though.. you'd need to use an adjustable step-up boost converter to bump up the voltage.

Essentially though, by using a constant brake application and constant throttle, along with a WBO2 logger, you could map out the power vs fuel delivery for each RPM point.

Then you could use the figures to tune for economy (set AFR's to where power drops off, shown from RPM's), or peak power (where RPM's peak).

I know the ECU has a voltage compensation for injector timing based on a feed from the injector's B+ back to the ECU, but that's easily bypassed.

This method would be much easier than endless logging run/retuning cycles to find peak power/econ values. And cheaper than dyno time, which with a J3 chip isn't realtime anyhow.

Anyone heard of this kind of thing before? Think it has potential?
I'm capable of developing it into a workable solution that could be replicated fairly easily if it proves to be a good idea, and if there's enough interest.

Feedback welcome :)
 Post subject: Re: Idea: Tune power/econ AFRs by altering injector voltage?
Posted: Sun Jan 13, 2013 9:48 am 
Getting Side Ways
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Posts: 1140

Joined: 27th Feb 2005

Ride: Supercharged EF Fairmont

Location: T.I. Performance HQ
VIC, Australia

Tuning cruise AFRs using the J3 shouldn't require many trial/error cycles, as long as you have a working o2 sensor and haven't disabled adaptive learning. Just set your target AFRs, then set your cruise MPG mode AFR adjustments. Once the fuel side is close (within your adaptive thresholds), adaptive learning will bring it in.

Also, don't forget the impact ignition timing has on fuel economy, sometimes there are greater gains here than on the fuel side.

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