MoTeC Global Forum

Hi,

we have a customer with a two-rotor RX-7 FD, single turbo. The customer wanted this ECU in his car, so we purchased and installed it. The car runs, but we have two issues:

1) We need help with the injector current setting. We have a pair of low impedance Bosch 800cc injectors for the primaries, and another set of Bosch 1600cc as the secondaries. When we had a current setting of 3A, the car would misfire at partial boost and we got an "OPEN" error on the 2P injector most of time, sometimes on both injectors. We changed this to 2A, and now we are getting a "PEAK" error. What exactly do these mean and what's the procedure for nailing down the correct setting?
2) At more serious boost levels, we are getting the "MAX DUTY CYCLE" error. By switching to the Balance table view, I can see that the primary injectors are reaching or exceeding 100% duty cycle, however the secondaries are more like 5-10%. I read somewhere in this forum about a formula to populate the Balance table properly (something like % = {1/[(S/P)+1]}. Right now the balance table is 100% everywhere, which means that only the secondaries are used, right? If so, why am I seeing the primaries being maxed out but secondaries only getting 5-10%? So my question is what do I do to get the secondaries to inject more?

Thanks,
Dimitris@Rotary Beat

Hi,

What is the resistance of the injectors and do you have the injector part numbers?

The injectors are 2.2 Ohms. I'll get the part numbers as soon as I can.

Ok the primaries are Siemens/Deka 3145 injectors, 750cc/min. The secondaries are Bosch 0 280 150 846, 1600cc/min. The primares are 2.2 Ohms, the secondaries are 4.9 Ohms.

The Balance Table sets what percentage of the Main Table fuel comes from the primaries. If you set the whole table to 100% the ECU will deliver all the fuel you ask for through the primaries which means you are going to run out of injector.

You need to lower the number in the balance table so that the fuel starts coming out of both injectors, for example, if you simply changed the balance table to now be 50% you will get exaclty the same amount of fuel as before but half (by volume) will be coming out of the primaries and half out of the secondaries which means the duty cycle on the primary will drop.

For the injector current you will need to compromise and have the setting for the injecotrs that need to highest current which will be the 2.2ohm injectors. The 4.9 ohm injecotrs will not draw that current and should give a peak error. The peak error simply says the injector output hasn't got to the current you said it would which is not really a problem. There is no way in the M4 based ECUs to set different currents for primary and secondary, you can either buy two sets of the same resistance injecotrs or change to an M400 ECU.

Thanks for the help!

The settings for the balance table worked and the secondary injectors now come into play.

I'm still a little unsure about the injector current setting. What is this number supposed to represent? The maximum current that should be allowed to flow through the injector? Isn't this dictated by Ohm's law anyway? Supposing that the car works at a stable 13.5V, and the primary injectors are at 2.2Ohms, then the max current that can flow is 6.1 amps. What should I set the current setting to?

Thanks again!