mark kibort

Fletch, and Virbus,

Ill try and answer the questions in one shot.
yes, the 83-84 cars.(I think down to 82) all us the Ljetronic, AFM style in the US. euro had CIS 300hp 4.7 liter cars till, 83 and then 310hp MAF until 85.

Virbus, The fuel regulator on the US doesnt vary the pressure via the vacuum imput. that vacuum imput is either on or off. it is connected to part of the Throttle body that has vacuum under idle. once the throttle is pressed, the vacuum is removed and full pressure of that regulator is applied to the system. same thing with the rising rate regulators. the vacuum line is for idle reduction of pressure, thats all.

the spring pressure on the diaphram, tells you what pressure the lines will hold, and how much fuel is returned to the tank. more fuel returned to the tank, the lower the overall rail pressure.
adustable regulators alow that spring force to vary.

Darren, shoot me over that pic if you get a chance. Did you ever get a close look at his car?
those audis were incredible!!
thanks!!
Mkibort@compuserve.com

MK

hacker-pschorr

FYI on the idle switch - on a supercharged L-jet 928, connect the switch.

Long before I installed the blower, I removed the vacuum limiter based on advice from many L-jet guru's. I then had the problem of RPM's dropping suddenly, almost killing the engine. The fix for this was to disconnect the idle switch. Life was good.

Fast forward to the blower – installed spring of 2006.

From day one my 928 would have lean spots under cruising. Roll into the throttle at 25mph, the car would not really want to do anything, Air / Fuel would be off the chart lean. Give it a bit more gas full rich and away we go.

After replacing everything including three different AFM, O2 sensors, ECU’s, upgrade to a 3-wire O2 sensor etc….nothing fixed the problem. So I cranked up the fuel pressure under vacuum to allow me to drive the car while I further tried to fix this. In the end I did find some other issues searching for this (mostly vacuum leaks). So overall this issue helped fix a few other things.

On Friday Z didn’t like the idea of disconnecting the switch. Once reconnected PRESTO!!! Problem solved. Car now drives perfect & I have fuel pressure back to stock. My RPM’s do not drop when I close the throttle – maybe the extra air form the supercharger is the reason.

mark kibort

the fuel cut off switch has no bearing on anything unless you are off throttle on decel. even on idle it really doesnt effect anything, as most of the fuel presure and flow is based on barn door position and idle air meter screw. all that it really does is cut the fuel when you are off the gas.. If you removed the full throttle switch, then that would certainly be BAD. at 75 % full throttle, it engages and enriches the fuel mixture 15% or so. you go way lean with out it. however, the off idle switch is never even used unless you are idling or off the gas. you would NEVER know it was connected or disconnected crusing at some part throttle situation (ie ANY rpm above 1000) and then you floor it.

And now, after that other discussion, i put the vacuum back in the fuel regulator circuit. it then didnt have throttle response for bliping throttle and downshifting in race conditions. disconnected it, and it came back. now im always at 72psi fuel pressure.


Mk

hacker-pschorr

Mark,
I cannot explain why, just reporting what my car is doing. If I disconnect the off idle switch - my car runs horrible with stock fuel pressure under a light / moderate load while under vacuum.

PorKen

It is right near the distributor, maybe the disconnected wire is picking up RF?

Have you checked the idle switch and/or ground ohms at the ECU connector?

hacker-pschorr

At this point it's running so perfect with the switch connected I'm going to leave it.

mark kibort

are you sure that is the "off idle switch"? Here is a quick fact. when you are just a hair on the throttle, the switch is NOT PART of the circuit. basically, when you are anything but IDLE, the switch may as well be gone. you can only hear it "click" on at idle (OFF THROTTLE) any other performance changes that occure at part throttle have NO WAY of being related to the idle switch. that i will stake my reputation on and bet you any amount of money.

as i also posted the actual vacuum effects for the fuel regulator. at cruise speeds, there is very little pull back vacuum on the regulators. only a few psi at most. most of the fuel control at this point is the modulation caused by the o2 sensor and the Ljet computer to reach cruise lean conditions.

at 75% throttle, the other switch is engaged and that is important to fuel air ratios at higher loads. however, it should still run well. I only know its an issue, as i measured air fuel ratios under this conditions for a test. also, its a signal for the system to go open loop (ie ignor the o2 sensor)

Its the black and white wire or the black and wht/black wire sets. i forgot which one is which, but i think the black and white wire are the idle switch wires.


mk

V2Rocket

Am I reading correctly in thinking that stock L-Jetronic will work fine with a supercharged engine?

hacker-pschorr

Yes Mark, I know I'm talking about the correct switch & it's hooked up correctly.
Only if everything is working 100% as the factory intended.

I would also get the factory CAT off the car and better yet - the factory cast iron manifolds before supercharging.

V2Rocket

100% as factory intended? So an unmolested, all-wires-plugged in L-tronic is factory?

What benefit would returning to iron headers bring? And yes, the Cat would come off.

hacker-pschorr

Um, take off the cast iron manifold with the CAT