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Trigger
Note:
- The trigger is just for RPM
- Is only used for fuel control
- there is no ignition control with this application as the stock Suzuki ECU takes care of that
The plan was to use a wire connected to the negative pole of one of the ignition coil primaries. We are now testing and 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 tried this approach as well.
- stock ECU injectors are high impedance, no PWM signal to worry about
- Primary trigger type : Hall
- R30 10K pull-up mounted
Overall it works out quite well!
Problems:
- Sometimes triggers on noise, quite obvious here : [datalog200707302242.xls]
- Suspected loss of some trigger events here : [datalog200707302244.xls].
- Not so easy to see in datalogs, but very apparent from freezing rpm gauge in MegaTune.
- The loss of events do not affect fueling so much that it causes lean problems, but should not be there.
Configuration file : [megasquirt200707302254.msq] (for firmware 1.0.73)
We did not get to test out a few things, so here are a few things I will investigate tomorrow night:
- We have triggered on falling edge, will try rising as well
- Input enhancements:
- Remove R56 which is connected to LM1815 that is not in use
- Add 10K across D14 or C102 (pulldown to GND)
- Increase the value of C102 (currently 2nF)
Notes about the datalogs:
- Engine is not fully tuned, runs quite rich on boost and due to using the stock ECU also on low load with a worse than stock exhaust manifold and lower compression ratio.
- Voltage is suffering a bit, due to not fully charged battery and a struggling voltage generator (35A) from the small engine.
- Lack of a TPS makes it difficult to see what is actually happening, and why, when MAP and rpm fluctuates.
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 high voltage
The voltage at igncoil primary is a bit high (also, dangerous to your health and your equipment).