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2010 Thruxton fuel injector wires showing 12v, but no current

3K views 18 replies 6 participants last post by  Ripper 
#1 ·
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?
 
#2 ·
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".
 
#3 ·
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.
 
#4 ·
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.
 
#9 ·
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.
 
#7 ·
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.
 
#10 ·
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.
 
#12 ·
I'm just wondering how this fault started, you may be able to gain some clues from the circumstances, you seem to be throwing a lot of parts at a bike that just happened not to start one morning, is there more to it than that?
good suggestion above about putting everything back to standard and maybe having a rethink, you can get lost if you change too many parts.
 
#14 ·
Have you removed either the MAP sensor connectors from the MAP sensors and refitted them, or removed the MAP sensors from their vacuum hose?

If the MAP sensor wires are not in the correct position the "firing" sequence of the injectors will be wrong and the bike won't start
 
#15 ·
If the MAP sensor wires are not in the correct position the "firing" sequence of the injectors will be wrong and the bike won't start

Good point.


The wiring loom for the Right hand cylinder MAP sensor is clearly marked with red tape. Check that.

Right cylinder is when viewed from the top or seated on the bike. The manual calls it Nº2 cylinder.
 
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