L-Jetronic Air/Fuel Ratios

[Henna318i]

I need to draw upon the historical knowledge of this forum. I  own a 1984 BMW 318i with 125k miles on the 1.8 L M10 motor. A couple of years ago I asked this forum about options for increasing hp from this motor. The two takeaways from that inquiry was that #1: There is no substitute for displacement and #2: Start with a fresh rebuild. So following those recommendations I sourced another 1984 1.8 L M10. After machine work it now has a 2002 crankshaft and a 1mm overbore with “custom” JE 9.6:1 pistons. The head has been rebuilt with a reground 284 degree camshaft, fresh valve job, seals, rockers and shafts. I now need to do final assembly and get it installed. My preliminary plan was to conduct the “ break in” with the existing L-Jetronic injection system that I completely refurbished a couple of years ago. Plans include a wide band O2 sensor. Ultimately I want to go with an aftermarket ECU. So now for my question. Can anyone who previously had a L-Jet EFI conversion provide me with info of what kind of air to fuel ratios I can anticipate? I am concerned that a overly lean condition during the break in could occur.

Edited March 25 by Henna318i
Reduce type size

[tzei]

I once put such a system on 2.0 std engine and it was fine. You can fiddle with AFM flap tension spring & FPR if needs be.

[Preyupy]

The L-jet system is airflow based so the theoretically it should compensate for the increased displacement at the lower engine speeds and throttle settings.  You should install a wide band O2 sensor and monitor it.  My main concern would be full throttle higher RPM as you might run into max fuel delivery and go lean.  My recommendation is staying richer than 13:1 under load ( you will see much leaner than that under very light loads and decel). You can affect mixture by adjusting the clock spring inside the Air Flow Meter. The 6mm mixture adjustment screw will only  change the idle mixture with very little change in off idle mixture.

[Henna318i]

Thanks for your responses. I was hoping I could proceed down that path before getting into wiring and programming an aftermarket ECU.

[TobyB]

+1:  as long as you monitor it, it should be OK. 

 

A long time ago on that same system

(on a different car)

I remember that altering the coolant temperature sensor's input

to the DME was also a way to 'trim' fuel delivery.

As well as fuel pressure, of course.

 

t