2010 Thruxton fuel injector wires showing 12v, but no current - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 19 (permalink) Old 09-13-2019, 06:42 PM Thread Starter
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2010 Thruxton fuel injector wires showing 12v, but no current

I have a Thruxton that refuses to start. It turns over, there is spark, but injectors are not opening. Using another Thruxton to switch parts. Have switched ECU, gas tank, crank position sensor, all relays, throttle body. I have check the wires coming into the injectors. They read 12.2V, but will not light a 12v LED. Checked current and it’s about 0.04A. Anybody have an clue as to what is happening? My guess is a short that is drawing off current, but where?
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post #2 of 19 (permalink) Old 09-13-2019, 11:17 PM
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The +12 Volts are always present at the Brown/pink wire to the injectors. To fire them the ECU "grounds" the other 2 wires (yellow/pink and yellow/purple) in turn, i.e. allows the connection of the negative -12 Volts to each injector for a few miliseconds as it needs it.


The technique is common in the automotive world and it's called "negative switching".
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post #3 of 19 (permalink) Old 09-14-2019, 08:46 AM Thread Starter
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Thanks, so if the voltage is not breaking, then the injectors will not fire.

I have a digital multimeter when shows a drop of about 2 volts from brown wire to the two “”ground” wires when the motor is cranked. Is this typical?

When I apply voltage to the injectors the solenoids do fire.
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post #4 of 19 (permalink) Old 09-14-2019, 01:04 PM
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Quote:
Originally Posted by Malcolm Johal View Post
Thanks, so if the voltage is not breaking, then the injectors will not fire.

I have a digital multimeter when shows a drop of about 2 volts from brown wire to the two “”ground” wires when the motor is cranked. Is this typical?

When I apply voltage to the injectors the solenoids do fire.

I've never done that measurement myself, but a digital multimeter is not fast enough to follow the injector's pulse, that is the time the ECU energises them. At idle it's only around 2.7 milliseconds or so. Only an oscilloscope could display that.
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post #5 of 19 (permalink) Old 09-14-2019, 08:37 PM
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Quote:
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Thanks, so if the voltage is not breaking, then the injectors will not fire.
No, its the opposite of that. The voltage is permanently connected to the injector by the Brown/Pink wire and the ECU links the other two wires to ground in order to fire the injectors. You should find that your 12v LED will light fine if you connect it across the Brown/Pink and a ground point. Those two "ground" wires (the Yellow/Pink and Yellow/Purple), are only connected to ground for a fraction of a second, which would mean that with the engine at idle speed the LED would be receiving "pulses" of power which would light it up, but way too dimly to see. This is due to the "on" duration being much smaller than the "off" duration and the reaction time of the LED (it takes a couple of milliseconds for the LED to light).

Quote:
I have a digital multimeter when shows a drop of about 2 volts from brown wire to the two “”ground” wires when the motor is cranked. Is this typical?
Same explanation as above. A multimeter typically refreshes (takes a fresh reading) every 500 milliseconds or 1/2 second. The more expensive ones are quicker but not by much. Multimeters are designed to display static or slowly changing information. What you are seeing is not a voltage drop, but an "averaging out" of the off duration.

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When I apply voltage to the injectors the solenoids do fire.
That means the injectors should be okay. It would seem that apart from a wiring fault (poor connection) between the injectors and ECU, there may be an internal problem, perhaps component failure within the ECU itself. Unfortunately the only way to check that out would be by substitution. Perhaps your dealer has a spare lying around that you could try.
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post #6 of 19 (permalink) Old 09-15-2019, 08:02 AM Thread Starter
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I have 2014 Thruxton also. Been swapping parts. I think I have swapped everything but the harness. Rather than swap that, I am getting one off EBay for $80. Let see if it fixes the issue.
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post #7 of 19 (permalink) Old 09-15-2019, 10:45 AM
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Checking to see if the ECU is firing (temporarily grounding) the injectors can be done with a 194 bulb, common dash, or marker light on older cars available at any auto parts store. The 194 bulb doesn't have a metal base but two small wires to make contact in a bulb holder. Straighten the contact wires on the bulb and plug them into the connector that plugs into the injector. Crank the engine over and if all is well the bulb will pulse, indicating it is being switched on and off by the ECM.
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post #8 of 19 (permalink) Old 09-15-2019, 05:49 PM
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check fuse #6
if this has blown the there will be no power to the fuel pump relay (no whirring noise of the pump priming)

so your injectors may be working but there is no fuel to start the motor
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Last edited by mike-tt special; 09-15-2019 at 05:53 PM. Reason: initially gave wrong fuse #
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post #9 of 19 (permalink) Old 09-15-2019, 07:45 PM
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Quote:
Originally Posted by Malcolm Johal View Post
I have 2014 Thruxton also. Been swapping parts. I think I have swapped everything but the harness. Rather than swap that, I am getting one off EBay for $80. Let see if it fixes the issue.
You can't swap out the ECU of a 2010 for a 2014 since the 2014 uses CAN bus and won't let the engine run without the electronic speedo anyway. Also, how would you get the speedo to actually work without the sensor in the gearbox? It would make more sense to use the 2010 as a donor bike for the 2014.

Its sounding like the swapping of parts has landed you in a bit of a mess (I know, I could be wrong or misunderstanding something here), but my advice to you at this time would be to put everything back to original and instead of the harness, put your $80 towards a used ECU. There should be a sticker on the ECU and for a 2010 model I think the base map number is 20187.

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post #10 of 19 (permalink) Old 09-15-2019, 07:53 PM
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Quote:
Originally Posted by mike-tt special View Post
check fuse #6
if this has blown the there will be no power to the fuel pump relay (no whirring noise of the pump priming)

so your injectors may be working but there is no fuel to start the motor
Nice one Mike, I didn't think of that, though on a 2010 the fuse to the pump relay is #4. Fuse#6 is correct for the CAN bus models.

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