Leaner can mean cooler running, mixture experiments Options

[mightyohm]

When trying to tune to leaner running conditions and very light load the duty cycles of the injectors are so short tuning becomes impossible. A/F ratios would bounce between 13 and 17 and the car would buck slightly. Say good bye to lean cruise.

Dave,

You're not running a flyback board, correct? Do you think it would help with the short injector pulsewidths?

[DNHunt]

Jeff

I'm not running a flyback board, I'm running a resistor pack and a High resolution code that allows 10X more resolution in tuning times. That helped helped some but the really is that short duty cycles are very hard to tune.

Dave

[lapuwali]

Injectors are mechanical devices, after all, and they don't have super quick opening and closing times (on the order of 1-2ms for each, so minimum useful pulsewidth is roughly 4ms). You could help yourself out by just raising the fuel pressure some, and lowering all of the pulsewidths to compensate. That may be enough to gain some headroom in the idle range. What fuel pressure are you running now?

I've heard a rule of thumb that states that 20%-80% is the range of duty cycle that allows reasonable control. However, that's also an old rule of thumb, and injectors have changed some in the past 20 years.

[DNHunt]

I hope I didn't mislead anyone. I'm perfectly happy with the way my car runs. It wants to run a lttle richer than I thought I could achieve at light load. So, I use a little extra fuel. It drives real well.

The point I was trying to make was I assumed I could get the engine to run leaner than stock because I could control the injectors better than the D-jet system. Not so, the limiting factor was the injectors. Possibly the engine would run leaner and stay cool but I couldn't do it.

I suppose that more tuning (changing the fuel pressure and injector pulse widths or changing injectors) could have helped but, I was satisfied so I stopped and have driven it for over a year.

Dave

[Dave_Darling]

....I hope your car has full ignition advance at 55mph...

Most 914s aren't, unless you've got non-stock gearing, a non-stock distributor, or tiny little tires. 55 MPH is about 2800 RPM. That's 200 RPM below the point where max centrifugal advance is reached in most 914 distributors.

--DD