Great minds think alike (although I'd doubt there'd be any money in it) . I've never yet been able to find a schematic for the Hella-made controller. Should be pretty easy to trace out the circuit, tho'. There is what I assume to be some kind of ASIC in it - I'd doubt it's brainy - presumably a bit of cranking logic to implement the state machine for the heater. With a simple microcontroller with a couple of A-Ds, should be quite easy to replicate it...there aren't many states or "rules" for operation. You've got to monitor the supply voltage, monitor the two heat switches, implement the startup and shutdown sequences, and pulse the pump when it's running. The key as you say is pulsing the metering pump so you you get the right combustion. The pulse spacing is all that sets the fuel flow. From memory, the pulse rate is I'd say abut 2 - 4Hz on my (brainy) B1LCC. I've got a B1L as well, but it's broken, so I can't measure it... If you were *really* clever, you could replicate operation of the B1LCC, mebbe. Instead of just shutting off, switched by the thermostat (and drawing heaps of glow plug current when it starts again), the LCC slows down the fan and (presumably) reduces the fuel flow pulses, so you get three heat settings. It monitors either an internal or external temperature sensor (just a thermistor in an expensive box) to switch between them. Got to be possible...
About 4 pulses a second from memmory as I sit here imagining it. Next time I'm in the bus I'll count pulses for a minute and get more accurate. It's possible the jet or whatever it is regulates the input and the pump merely provides enough pressure but not too much? I can't see the pump as a very accurate metering tool.
The pump is metered and suplies a set amount of fuel, if you look closely at the pump you will see there is a nut on one end that's to set the volume of fuel injected, on earlier eberspacher the fuel is pulsed one per revolution of the main fan, the e earlier ones have a set of points that run off the fan shaft and there is a flat on one side of it, I think the coil and heater plug must pulse off the same thing, there is a thermostat unit in the air flow to control temperature. Not sure how the new ones like zed has fires but it must be off fan speed somehow. The shut down cycle is most likely just run off the thermostat with an extra feed which is cut when the temp drops. I have a BA6 the newer control unit is just an electronic version of the earlier relay set up. I spent a long time trying to find info and there is not much about but I pieced together bits from here and there to get mine running
I have altered a pump to get it to run another model, as described above, i just used trial and error but there are some measurements here http://www.letonkinoisvarnish.co.uk/Eberspacher_Fuel_2.html
Top stuff ! I do like an enquiring mind... As above, it is both the heater jetting and pump volume that set the combustion rate. Bit of trial and error necessary, I reckon. FYI, folk who are desperate for earlier Ebers spares (B/D1L onwards) might try the bloke on eBay (search for Eberspacher). He's based in Turkey, but seems to have an endless supply of NOS bits.
