- The trigger is just to get an RPM signal
- VEMS is only used for additional fuel
- Ignition control with this application is handled by the Suzuki ECU
We are now using the ground signal from one of the fuel injectors.
Using the ground signal of a stock ECU controlled fuel injector
The ground signal for the #1 injector is used as the trigger in the [MC Xpress turbo kits], so we are using this approach as well.
- stock ECU injectors are high impedance, no PWM signal to worry about
- Primary trigger type : Hall
Overall it works out quite well!
We have done these input trigger circuit enhancements:
- Removed R56 (10K) which is connected to LM1815 (not in use)
- Removed R30, the pull-up is not needed with this input signal
- Added 6.8K across C102 (pulldown to GND, 12*6.8/16.8 = 4.86 Volt)
- Increased the value of C102 to 10nF (is 2nF originally)
Note: There can be mistriggering sometimes when full throttle is applied, the stock ECU adds a lot of acceleration enrichment which creates this problem. But it is not an issue, one just has to be aware of it while tuning.
Using the rpm gauge output from the stock ECU
With a DVM the output was measured to have 13.4 VAC and 6.6 VDC towards ground. The signal strength is very low, so very high resistance is needed on the trigger input so not to disrupt the signal to the rpm gauge. It turns out that we better remove the R30 10KOhm pull-up towards +5V to get a good reading.
Using the stock crank trigger
Note: This method has been ruled out due to uncertainty about conflict with the stock ECU
Currently tested is the crank trigger, it is a VR sensor and is used with the LM1815.
- Measurements show 170 Ohm, 700 mV amplitude at idle
Test 1 : 10 uF in series with trigger wire = weak at low rpm, functions well at higher rpm but stock ECU cuts out.
Test 2 : Added 220uF in parallel to the 10uF from first test. Same scenario, even weaker low rpm and stock ECU cuts out.
Measurements show 1.5 Volt AC and 3 Volt DC at idle. (between signal ground and trigger input). This is obviously a problem, I don't know why the bias voltage is as high as 3 V.
The stock ECU only cuts out when load is put on the engine at which point ground currents probably increase and cause interference. While free-revving the engine with no load there is no cut out, but as soon as full throttle pulls are made the ignition is cut.
Using the ignition coil primary ?
Note: This method has been ruled out due to high voltage
The voltage at igncoil primary is a bit high (also, dangerous to your health and your equipment).