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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. The stock ECU injectors are high impedance, so there is no PWM signal here. Current test setup consists of:
- Primary trigger type : Hall
- R30 10K pull-up mounted
- 270 Ohm series resistor
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]
We did not get to test out a few things, so I have a few questions which might save some time on next occassion with the car.
- Triggers on falling edge, should it be rising?
- Crank min. period was set to 0. With 1 pulse every other crank rotation and 13000 rpm gives : 2x60/13000 = 9.23 ms between trigger events.
- Currently using 270 Ohm series resistor, is that too much dampening?
- We tried 1KOhm first with similar problems and it seemed worse.
- Could it be removed altogether? Afraid to damage trigger input without further advice.
- Should the R30 pull-up resistor be removed?
- Will the stock ECU take care of the majority of the flyback voltage or is there a need for extra flyback protection?
Notes:
- 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.
- My USB oscilloscope is still not here..
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).