10 Amp fuse blows, now and then
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250 Super
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Thu May 23, 2019 2:43 pm quote
The 10 amp fuse that powers the fuel pump on the 250 Super will occasionally blow. I've checked the wiring harness at the front of the pet carrier and the wiring and connector seem OK. The fuel pump had been replaced a few years ago under the recall program. The fuse seems to blow mostly when starting to accelerate the engine from idle, as in starting out from a stop sign or adding power after coasting slowly down a hill. Any trouble shooting tips or ideas?
Molto Verboso
Kymco AK550
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Thu May 23, 2019 11:50 pm quote
I would temporarily replace the fuse with a slightly higher rating, say 15 amps but no more. If this also blows then you have an intermittent short circuit which must be found even if that means going right back to the pump itself. If it doesn't blow it should be inspected after a few hours of riding to look for any signs of heating of the fuse element itself. If there are no indications of a further problem its probably safe to leave the higher rated fuse in place.
The circumstances in which it blows are probably when the pump cuts in after being off-load, so likely to be related to a surge issue. You should also check that the battery voltage never exceeds 14.5 volts when you rev up the engine. If the regulator is malfunctioning it is possible that the fuel pump fuse is just the first thing to be pushed over the current limit by a too high voltage.
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Fri May 24, 2019 12:17 am quote
Do not put a 15amp fuse in a 10amp circuit. That is the best way to cause a big problem and damage a component or wiring especially if the Rectifier is bad.

The fuse blowing can be caused by multiple issues, but an often overlooked problem can be a poor earth to the frame from the motor. Another is the rectifier earth to frame. That's an important one. In fact, I've found that when bikes come into the workshop with similar issues a poor earth has been responsible for this very issue. So check as many earth points as you can (in particular the Rectifier earth) and give them a good clean. You can identify them from the electrics page in the workshop manual. Use some dialectic grease on them, just a little. Or, some Vaseline if you don't have anything else.

Of course the Rectifier could just be going bad and as roadster says, check the voltage at the battery with the motor running at idle and when revved up. If it blows after idling that's a crucial time as the current generated goes up quickly.

If the Rectifier is ok and all earths ok, then check for any obvious problems with the wiring harness eg: exposed or chaffed wiring etc. Please report back on what you find.
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The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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Fri May 24, 2019 7:39 am quote
That fuse also feeds the coil and injector - so if the grounds and voltages are OK as above then don't forget these when inspecting wiring.
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250 Super
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Fri May 24, 2019 5:33 pm quote
I'm hesitant to try the 15 amp fuse, not knowing what kind of margin the engineers have in their circuit protection. I will check all the aforementioned grounds. I hope it's just a ground i$$ue, but will re-check the wiring at the front of the pet carrier as well.

Is the ecu/ecm (don't recall the exact nomenclature-is that the same as injetor?) on the same circuit?
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Sat May 25, 2019 8:14 am quote
classic rider wrote:
Is the ecu/ecm (don't recall the exact nomenclature-is that the same as injetor?) on the same circuit?
No. Look at the circuit diagram. The feed from the fuse goes through the 'injection loads' relay and onto only the three items above.

https://manuals.wotmeworry.org.uk/Vespa/GTS250/
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250 Super
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Sat May 25, 2019 9:59 am quote
jimc wrote:
No. Look at the circuit diagram. The feed from the fuse goes through the 'injection loads' relay and onto only the three items above.

https://manuals.wotmeworry.org.uk/Vespa/GTS250/
Thanks for the link. If I followed the lines correctly it looks like the lambda sensor is also on that circuit.
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Sat May 25, 2019 10:27 am quote
classic rider wrote:
jimc wrote:
No. Look at the circuit diagram. The feed from the fuse goes through the 'injection loads' relay and onto only the three items above.

https://manuals.wotmeworry.org.uk/Vespa/GTS250/
Thanks for the link. If I followed the lines correctly it looks like the lambda sensor is also on that circuit.
Yes, sorry, my eyes deceived me!

So also look for chafing and perhaps an intermittent short to frame on the Lambda sensor wiring.
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Sat May 25, 2019 5:25 pm quote
Yup, reading those wiring diagrams is like viewing op art-everything is spinning and moving around. The voltage seemed nice and steady from idle to higher revs, although the steady state battery charge might be down a bit at 12.5 volts. The wiring seems to check out. Grounds seemed clean and solid as well. The only other "connection" to the 10 amp fuse is the fuel injection load control switch (relay) that the power passes through.

I'm wondering if the fuel pump might have a bit of grit in it that could lodge when the demand is low at idle, then stalls the pump leading to an overload condition when accelerating the engine? I really don't want to $tart throwing components at it in hopes of fixing the problem. It ran just fine to and from the store for some more fuses.
Molto Verboso
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Sun May 26, 2019 12:35 am quote
Failing anything else you could check the current in normal conditions with a multimeter on 10 amp setting. Its not a good idea to run a meter in place of the fuse so you should try to make a connection in series with it but keeping the circuit fused at 10 amps. If you find the load is edging towards 10 amps then it is probably a bit higher than originally designed. As a rule of thumb you wouldn't expect a circuit fused at 10 amps to draw more than 5 amps ( allowing for surges when switching on etc.).

According to Jim's manual the fuel pump should draw around 2 amps when the fuel return pipe is blocked. If the fuel pump is responsible then it needs to be checked to see if it has a clogged filter or some other condition which would put high load on it such as a pressure regulator which has stuck.

Incidentally reading the manual rather than the main wiring diagram it looks like the cooling fan control relay also runs from that fuse.
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Sun May 26, 2019 8:04 am quote
I'd believe the diagram rather than a written description - especially after the Italian-English translation.
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Mon May 27, 2019 6:39 am quote
While checking the wiring I noticed the diagnostic connector. Would hooking that up to an analyzer provide a clue to what's causing the fuse problem? Of course finding one could also be a minor issue.
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Mon May 27, 2019 6:48 am quote
Diagnostic tool won't help with this.
Try doing a wiggle test to see if you can get the fuse to blow. Just start wiggles the wires too see if the fuse blows. This is a sophisticated test Ford invented.
Well they were the first to use it as a proceed in a manual.
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Thu Jun 13, 2019 6:26 pm quote
Follow up including this thread 250ie Fuel Pump Questions (issues?) as well:

The wiggle test was OK, no wiggles caused fuse blowing. The fuse started to blow while the engine was at riding RPMs as well so I've installed a new fuel pump. No further posts will indicate that was the fix to the problem.
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Thu Jun 13, 2019 7:15 pm quote
Well if your fuel pump messed up twice it accords well with my theory, based on a life of observation, of the magnetism of problems. Seems all of my problems were cooling system related. Hopefully that will be the last of it.
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Fri Jun 14, 2019 12:03 pm quote
Drat, the fuse is still blowing. On the positive side I now probably have a spare fuel pump. The theory of the magnetism of problems seems to apply here, now to solve the equation.

Back to checking the wiring, again. Just curious, will the engine run with the lambda sensor disconnected? That is one item on the circuit.
Hooked
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Fri Jun 14, 2019 12:12 pm quote
i agree with the above thoughts that suggest it might be a bad ground...a wire is touching something that its not supposed to
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Fri Jun 14, 2019 7:04 pm quote
After studying the wiring diagram some more, would an insulation problem causing an intermittent short circuit in the wiring from either the fuel injector, ignition coil or lambda sensor to the miu cause a fault that would read out on an analyzer while at the same time causing the fuse to blow (as if that component had failed)?

Or, could there be an internal failure in the miu that was "shorting" out the circuit for one of those components connected to it?

Another question, would jumping contacts 30 and 87 on the injections control relay and connecting an amp meter turn on the pump directly and bypass the other components on the circuit since the pump only goes to ground, not the miu? That way I could leave the fuse in place.
Molto Verboso
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Sat Jun 15, 2019 12:09 am quote
classic rider wrote:
After studying the wiring diagram some more, would an insulation problem causing an intermittent short circuit in the wiring from either the fuel injector, ignition coil or lambda sensor to the miu cause a fault that would read out on an analyzer while at the same time causing the fuse to blow (as if that component had failed)?

Or, could there be an internal failure in the miu that was "shorting" out the circuit for one of those components connected to it?

Another question, would jumping contacts 30 and 87 on the injections control relay and connecting an amp meter turn on the pump directly and bypass the other components on the circuit since the pump only goes to ground, not the miu? That way I could leave the fuse in place.
Why not simply put a meter on 10 amp setting directly in series with the relay using the connector on the 30 terminal and the terminal itself? If the typical current is more than 5 amps then investigate further down stream to see where the extra load is coming from. The next load is the lambda sensor heater feed ( black and green at sensor connector). This is a resistive load which runs hot by design so it could easily be partly shorting given that it is in a hostile environment. Having eliminated the fuel pump you also have to check the ignition coil and the fuel injector because these are also fed by that black and green wire ( if I'm looking at the correct wiring diagram).
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Sat Jun 15, 2019 8:08 am quote
roadster wrote:
Why not simply put a meter on 10 amp setting directly in series with the relay using the connector on the 30 terminal and the terminal itself? If the typical current is more than 5 amps then investigate further down stream to see where the extra load is coming from. The next load is the lambda sensor heater feed ( black and green at sensor connector). This is a resistive load which runs hot by design so it could easily be partly shorting given that it is in a hostile environment. Having eliminated the fuel pump you also have to check the ignition coil and the fuel injector because these are also fed by that black and green wire ( if I'm looking at the correct wiring diagram).
Sounds as if we're looking at the same diagram re. wire colors. In addition to chaffed wiring to the lambda sensor, could the heater itself short and cause enough current to blow the fuse? I've googled lambda failures and didn't see that as a symptom.
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Sat Jun 15, 2019 12:02 pm quote
Update: After connecting all the harness back up the fuel pump did its 2 second pressurization run but the scoot wouldn't start (cranked over, no ignition). Discovered the wiring connector for the fuel injector had broken loose. Research indicates that an issue with the design. Rather than the vintage fix of JB Weld I used a couple of zip ties to hold it in place, and the scoot now starts an runs. So far the fuse hasn't blown again (yet?). Could that fitting have caused a random short, blowing the fuse?

fuel injector.jpg

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Sat Jun 15, 2019 3:21 pm quote
Yes. JBweld for right now perhaps - but replace with new ASAP.
Molto Verboso
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Sun Jun 16, 2019 12:28 am quote
classic rider wrote:
Sounds as if we're looking at the same diagram re. wire colors. In addition to chaffed wiring to the lambda sensor, could the heater itself short and cause enough current to blow the fuse? I've googled lambda failures and didn't see that as a symptom.
I don't know anything about the innards of a lambda sensor. If the heating element is a tungsten wire I suppose it could flap about if it breaks then short out somewhere, but that might put the engine management light on. If its a carbon film then could it get some contamination on it that would lower the resistance? No idea really but its more likely to fail open circuit than short circuit!
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Sun Jun 16, 2019 12:48 am quote
Yeah, they fail 'open loop' so motor will run rich. No signal goes to ecu.
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Sun Jun 16, 2019 3:18 am quote
classic rider wrote:
Drat, the fuse is still blowing. On the positive side I now probably have a spare fuel pump. The theory of the magnetism of problems seems to apply here, now to solve the equation.

Back to checking the wiring, again. Just curious, will the engine run with the lambda sensor disconnected? That is one item on the circuit.
Yes it will.
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