Modern Vespa

I have a 2006 Vespa GTS 250 IE 18K miles. I had a meltdown with fire a year ago and had to replace the wiring harness. Since then I am unable to ride more than 3-4 miles before my bike begins to miss, sputter, stammer ect and I loose speed and all acceleration. This is also the time that the bike has reached normal "hot"operating temperature per the gauge.

This is where it gets weird.

If I unplug the main wiring bundle going into the ECU for 10 seconds I can get back on and ride fine afterwards. This is obviously not a durable solution and I have lost confidence in the bike. Please help if you can.

Thank you all in advance for any advice.

My thought is replace the ECU but not sure if it makes sense given the symptoms.

Make sure the positive terminal of the battery is not shorting out against the side of the body. That's what usually causes this meltdown in the first place, and will cause the symptoms you describe. Check for little black marks, signs of arcing, on the body where the positive terminal might be touching when it's ridden.

I have the battery well insulated as I suspected this may be an issue that contributed to the fire in the first place.

My two cents: So, the engine gets warmed up and quits, right? What is happening when it gets to this stage is that the water temperature sensor is sending a signal to the main computer, the ECU I suppose, to tell it to close the enrichment part of the fuel system. So my guess is that the temperature sensor has gone a little wonky and should be replaced. If that does not work, it is probably the ECU itself. Of course, check the wiring all the way down and back to make sure that it is not shorting out anywhere.

Does it continue to run normally for the rest of the ride after you unplug the ECU?

When the signal from the water temperature sensor is telling the ECU that it's not up to operating temperature it will inject a richer mixture. If you had a vacuume leak it might run normally until it warms up and it leans out the mixture. At that point the additional air from the vacuume leak would make the mixture too lean. Just an idea.

since you changed the harness have you heard/seen the cooling fan go on?

Any flash codes?

John

Honestly I have not heard the fans that I can remember. Sounds interesting, what could this mean?

No codes

Sand all the grounds, put a tad of conductive grease on threads, reset ECU and tighten (just guessing)

I'm still learning the ECU, but it could be overheating. If someone knows what will trigger limp mode speak up.
I would also look at system voltage. Dongyerscoot suggested cleaning up the grounds and using some hydrocarbon grease I agree with that.

John

System voltage is good, fuel pump has pressure. I have not had any problems after disconnecting and reconnecting ECU....although I do not take it far as I do not really trust it anymore.

I would start it up let it idle like 10 to 15 minutes it should warm up enough to kick the fan on.

John

The man lives in Tampa - five minutes ought to do it.

FAN TEST:

Let it sit idling for 10 minutes, then slowly drove it up 6 floors of parking garage. then let it sit for 10 more minutes...no fans....had to get back to work.

Gauge did not get over 5 bars (middle of interval).

did it go into limp mode?

John

It did

I'm guessing here that high temp will put it in limp mode. I would hope the others in the know will reply. In the mean time I would find the fan relay or switch and jump it . Then go for a ride and see if it stays out of limp mode.

John

Swap the connections between the two temp sensors (one feeds the ECU, the other just the gauge).

It's possible the one feeding the ECU has gone duff, so is telling the ECU that the engine is still cold. I don't know how it acts on this info, but it'll either believe it and continue to run the engine very rich (which might seem to be limp mode!), or it'll disbelieve it and possibly go into limp mode.

Worth a try, anyway, as it's very simple to do.

Jimc, just a thought here. The sensor to tell the ecu the engine temp (thermistor) and the fan switch makes ground (opened or closed) . One reading resistance and the other making ground.

short one and fan comes on short the other you get limp mode.

I'm going to look this up in the diagram.

John

check fuse #7 15a


looks like they are both thermistor based, the gauge wires direct to the sensor. and the fan relay wires to the ecu. There is no switch.

John

Fuse #7 intact

can you locate the temp sensor, from the diagram looks like it has 4 wires.
gray/green
light blue/green
green/yellow
black

see if you can jump 30 to 87 on the fan relay, see if the fan will run.

http://members.modernvespa.net/cincinnati_john/uploads/gts250_electrical_diagram_793.pdf

John

Please, please, please - the fan not coming on is EFF-ALL to do with it as far as the reported symptoms go.

Indeed, if the ECU temp sensor (not the gauge one) was faulty, the fan never would come on even if the temp gauge showed it overheating. But it doesn't so why go chasing the fan???

Jumping wires goes beyond my skill set when it comes to electricity. I am will to read and try but it will take me a while to figure that out without destroying my harness.

the fan switch is pictured in the hoses between the radiator and engine, the temp sensor is screwed int the thermostat housing.
if you can locate the switch or fan relay that a good start.
Team viewer or skype to get a live look with audio?
John

item #39 on page 51
http://www.af1racing.com/store/ProdImages/st3/EVG4000US1.pdf

it is a fan switch it is not listed in the electrical diagram.

John

Why are you stuck on the fan? You are pointing him in the wrong direction.

Ok what is causing the limp mode what data input will trigger limp mode?
When it goes into limp mode do you get a flash code?

John

As above, the ECU getting 'out of gamut' sensor readings. In this case the ECU half of the temp sensor would be the first thing to test. No idea - but I very much doubt it.