Tom Faust

More fuel with higher boost is a problem we all know about. I have added an additional, boost operated, injector to my minivan. This is simple and solves the problem.

While looking at Audis, I have noticed that untapped 6th bung on the fuel distributor. Does anyone know if it is possible to tap that bung to add an injector? Is fuel pressure high enough to support it?

boxerfan

I've been looking into this. I think that it would be possible but a great deal of work as well. The CIS from a scrapped 911 should bolt on and add that 6th injector with less effort but more $. The fuel pump should have more than enough jam to cope with the extra fuel especially if run at full battery/alt. voltage.

Alternately, I have not completed this work yet, but a fuel line run from the CIS input to a warm up injector mounted in the intercooler MAS location (relocate to intake manifold - directly a bolt on fit at the optimal point for adding extra fuel!). The Audi warm up injector will not add enough fuel, but apparently a SAAB one will and has the same form factor (30lb vs 5 lb).

To ensure that I will have enough fuel volume and pressure I'll be adding a pressure activated relay to bypass the ECU control of the fuel pump. A second one will activate a fraction later and start the 6th injector.

Once those are in place I'll be adding an R mod on top of the QLCC chip and then crank down the 1.8 bar spring manually. I might also run straight boost pressure to the WG as well. Keep in mind that I currently have 3 spare engines at my disposal! I want to see just how much punishment they will take.

Tom Faust

It has been foud that the best position for the additional injector is just a few inches ahead of the air flow meter. Here is a link, it presumes electronic injection, but I don't think that alters the principles. Scroll down the page to find the section on additional injectors. Dawes Devices sells the pressure valve.

The author is deceased, but his web pages are maintained by fans. There is a lot of "low tech" "high tech" there.<ul><li><a href="http://home.earthlink.net/~tmahon281/fuel.html">http://home.earthlink.net/~tmahon281/fuel.html</a</li></ul>

boxerfan

Obviously you aren't completely satisfied with this set up. What is making you examine the 6th CIS position? What is your curect set up?

Tom Faust

I run 24 psi (indicated). That is on my minivan, I am completely satisfied with it.

I am toying with the idea of another Audi, but I am not interested in the expense and trouble of adding EFI to one. The EFI is more than I would expect to pay for the car.

Will Ng

By tapping its 6th bung, you will throw off the callibration of the other 5 outputs, and perhaps beyond the frequency valve's ability to maintain mixture ratio.
At least this is what I've read about the CIS distributor. Any adjustment to flow output to one bung will affect the neighboring ports.
With the 6th not flowing at all, suddenly opening it means the other 5 are off. Way off.
When you think about how supplementary injection should work...kick in when the stock setup's max is reached...IMO CIS can't be rigged to provide this. The stock 5 outputs are metered correctly for stoich. Start 6th output when 1.9 bar absolute is reached and the previous stoich output is lost. You've entered an unknown. If you tune all 6 outputs, that means the first 5 must flow lean and the 6th output is a constant throttle body injector to return to stoich throughout the boost range. That sounds like a tuning nightmare.

I think adding the electronic injector as supplementary 6th circuit is the logical way to go if you stick with CIS for cheap thrills. The trick is to come up with a cheap way to make it closed loop instead of the open loop we have in this discussion. Perhaps a wideband O2 circuit to drive the injector's duty cycle. Tap into the full throttle switch signal to make it fully open when needed.
And then there's water injection to keep things from grenading at the edge.

boxerfan

By indicated you mean absolute pressure? so that's 10 psi of actual boost? Or are you talking positive manifold pressure?

Tom Faust

"Absolute pressure" is one of those terms I have never got a handle on, although I do understand that ambient pressure is 14 and some change. I will have to look into it.

By "indicated" I mean that my pressure gauge reads a negative figure at idle and 24psi positive at full boost.

I know people who run more, but they have gutted the interior and removed the spare so that they can run in the 12's. I use mine for parts chasing and trips to Home Depot.

Don'tget me wrong about all of this, I like Audis. I think the newer A6's are beauties, but that they only equal without surpassing the Tyoe 44. It is all the gremlins which make me crazy.

Tom Faust

I see your point, I should have realized that being mechanical it would be important not to interfere with, or alter, pressures.

I only thought of using that bung for the "elegance" of it. What is your opinion of simply tapping into the fuel line to feed a pressure switched 6th injector that only operated at WOT. I suppose it would be best to tap into the line just ahead of the pressure regulator.

Got to admit I have never spent a lot of time looking into CIS, is the pressure regulated at the end of the fuel rail? Or, is pressure regulation part of the fuel distributors job? I seem to recall that CIS does not provide a schraeder valve to test pressure and that you have to tap into the fuel distributor.

Will Ng

to supply the 6th injector.

CIS fuel regulation is multi-tiered (or bodged to make it emissions compliant)... you have the warm-up regulator, then the standard pressure regulator before the fuel distributor, and the O2 controlled frequency valve before the fuel distributor.

I'm no CIS expert either. I just read up a bit on it and was amazed how complex it is. Only the f$#$kin' Germans could have made it work, and stubborn enough to continue using it for so long.
I find in that era, the Germans had an admiration and adherence for mechanical engineered solutions...and a fear of electrical engineering designs.
Hell, even Honda offered a relatively cheap car in '89 that offered digital sequencial fuel injection and VTEC that broke the 100HP/liter mark for a N.A. engine.

WOT only operation is safe for conditions that never see partial throttle....like down a drag strip. At partial throttle, depending on the gear you're in, you can go beyond safe boost limits if you have a stiffer wastegate spring installed and preloaded to go beyond 1.7-1.8 bar absolute. ie. 5th gear and you step on it, and boost creeps pass 1.8 bar and go lean. The 6th injector never comes online. Eventually, the engine goes bang!
That's why IMO using one of those $12 pressure switches is more desirable.
They are readily available at www.digikey.com