Hi KobaltBlau,

Yes, ideas come easy to me.
But back to the mapped frequency valve control. If you want to experiment with that, you could use a basic Megasquirt. It fires it's injectors in "batch" mode, at RPM * cylcount frequency. It should be very easy to modify it to run a fixed frequency and modify duty cycle only, but still retain RPM, MAP and IAT inputs for fuel map lookup. The frequency valve of course in that case is the "injector". This way you don't have to wait for us. ;)

Regards,
Klaus

I think I will do that, Klaus. Much appreciated! What about a TPS input, not needed?

I don't think so, MAP control should be enough, because most of the work is done by the CIS itself. The only thing the Megasquirt does with TPS AFAIK is accel enrichment. That can be done if neccessary via the slope (dMAP/dt) of MAP, as TBITZ's system does. The CIS has 'some' accel enrichment, they are using the overswing of the plate for that.
Regards,
Klaus

"A 3rd gear WOT run shows AFR not steady, but varying by over 1 AFR over the RPM range (11.9 to 13.1)"

Hardly worth all the design, cost, & engine mods for very very marginal
fuel economy and engine performance, versus the stock Bosch K-Lambda system.

Bottom line: Porsche/Bosch designed an excellent system for all around performance and economy.
Even changing to an EFI system will have marginal improvements. Read the thread on switching
to a Motec system for a stock engine, same basic discussion!

Read here: http://forums.pelicanparts.com/porsche-911-technical-forum/246074-motec-worth.html

For once, I'm with Loren on this topic.

K-Jet working correctly will always default on the rich side during open-loop operation. Trying to improve K-Jet by intricate schemes of modulating frequency valve is dead end, there is almost nothing to be won.

In my opinion, only way to improve K-Jet without replacing whole shebang with cheap EFI-setup would be some kind of step-motor powered actuator depressing fuel-head plunger. That would allow removal of metering platte which is K-Jet's biggest problem.

In the end, it means that you would run with fully fledged EFI with fuel-injection part replaced by electro-hydraulic K-Jet legacy parts.

That's an economic argument, not an engineering one, do you agree?

I have read many times that the O2 sensor SC's run better with the O2 sensor's unplugged - does simply unplugging the sensor accomplish some of what you are talking about? (though presumably it will decrease mileage?).

Hi,

Unplugging the O2 sensor makes the Lambda computer go open loop. If the CIS is adjusted right, it will idle and cruise at about 13 AFR. This makes it respond better, but decreases mileage.

I also disagree with the notion that the CIS can't be improved. If it would be already the best system, we would still have it today. But conditions have changed since it was designed. Gas is crappier, and parts wear out. So many CIS systems run outside their original design envelope. By closed loop control you can compensate for these conditions and optimize fueling to best performance (which BTW is NOT a flat AFR curve for the CIS).
Ignition is another part of the equation. A distributor with centrifugal advance and vacuum retard is a crude way to do it at best compared to todays technology. With programmable ignition you can optimize the advance curve to MBT in all conditions. This greatly improves driveability and response.

Regards,
Klaus

I'm reopening this gem of a thread as I've installed an MTX-L on my '80 SC and will soon do the closed-loop WOT trick.

My question is about the base mix (engine warm, sensor disconnected). IIRC it should be about 0.6% CO (14,2 AFR) but I assume that is a compromise for economy, cold starts, power etc.

Now that hot cruise and WOT is closed loop would there be any benefits to use a different base mix?

Cheers,
Björn

Any updates to this thread?

I may install an LC-1 with a wide band to tune the idle mixture. Just need to configure one of the other analog outputs to mimic the factory narrow band.

i've tried this and couldn't make it work.

The lambda brain perfectly accepts one signal from one of the analog outputs of the LC-2 (in my case), but switching between output 1 and 2, powered by the throttle switch, would not work on my car. I'm guessing that the split second it takes for the relais to jump to the other signal confuses the brain...i got weird afr results driving around with this setup.

The base mix will influence the running of the engine in all RPM's. So if you set the base mix richer, then the WOT fueling will be richer too.

In my experience (i ran for a while without throttle switch, just set AFR to 13 all the time through the innovate), the richer setting will improve throttle response a great deal. I tested with 14,7...14,2...13,5...13,0...and each time i could feel low rpm response improve quite dramaticly.

It's all in all a complicated setup, and some parts of it are not documented at all: for example the enrichment relay next to the lambda brain is a big mystery. (not the 'normal' relay that's located there as well...i'm talking about the little metal box next to the lambda brain)