ViribusUnits

How is the base ignition curve for the LH-jet computer created?

There needs to be some sort of system to take up for the lack of vacuum advance.

On the Fords it taken by takeing the results from the air flow meter, and divideing it by the rpm, to get a "Load" factor. The higher the load factor, the less ignition advance is dialed up. From there, the anti-knock sensors fine tune the timeing.

This is superor to the vacuum based advance because of the same reasons that Air Flow Controled EFI is superor to Speed Density EFI.

Can any one confirm or denie this for the Bosch control units as of 87+?

I can't make heads or tails of the wireing diagram.

Thanks.

Rich9928p

Fords use a combined fuel injecton and spark controller. The Bosch equivalent is called the Motronic.

The 928 has separate fuel injection and spark controllers. The LH-Jetronic has no ignition curve, it only manages fuel injection. The EZK spark controller contains the spark map. The EZK has a map of spark advance vs. RPM and load. The EZK detects spark knock and retards spark accordingly. The LH communicates load information to the EZK via one of the circuits between the two modules.

The 1984 (Euro) - 1986 928s used an EZF spark controller. That unit uses a vacuum line connected to the unit for load information.

ViribusUnits

I realize that.

I guess I wasn't clear. I was implying the EZK unit useing an input from the LH unit, or the MAF to calculate a "load" factor, and then do the base curve off of that.

How is the load calculated? If it's by the throtal body, thats not very accuret, as the throtal body switch only has three settings. Idle, cruise, and WOT.

Rich9928p

The LH injection controller injects a precise amount of fuel, either based upon its own map of injection time vs. RPM (open loop) or when "fine tuned" with the aid of the O2 sensor (closed loop mode). If you've seen the newer 928s with the board computer, they have a MPG (or liters per 100 Km) display mode. The instantaneous mileage readout is based upon the amount of fuel being injected. The same kind of information is made available to the EZF unit to aid in calculating spark advance. Also, each control unit is provided with engine temperature to compensate for that variable.

ViribusUnits

That doesn't answer the question I asked.

Let me restate it OK?

Does the S4 EZK computer use an input from the MAF, dirictly or indirectly, to calculate the ignition advance for the curve?

Rich9928p

yes, indirectly.

ViribusUnits

Thank you, I thought so, but I couldn't confirm it.

John Speake

ViribusUnits
The load signal from the LH to the EZK comes from pin 25 of the LH

Steve Cattaneo

The load mapping information for the LH and EZK on 1987 cars and up is the MAF sensor. By reading the MASS of the air passing thru it the LH and EZK selects the optimal fuel and timing maps based on the load of the engine. The LH and EZK also looks at other engine input such as engine RPM, 02 sensor , cam position, crank position , knock sensor and the throttle switch. External Modification such as changing the flow charactistics of the sensors without changing the map values can cause a drivability problem.

This load sharing information between the LH and EZK is thru pin #25 LH to pin#9 EZK