Modern Vespa

Hi, after a long trip yesterday, 6 km from home my MP3 just died on me. I made some troubleshooting on the spot. I should say that I had the check engine lamp come and go the last two weeks and I was under the impression that the fuel pump was giving up, in fact I ordered one yesterday morning to change next weekend...
However, disconnecting the fuel hose proved there was pressure there, same when I turned the key, plenty of fuel.
Checked the sparkplug, it's grey and produces spark. However, it was dry...
Oh yes, of course, I checked the fuses beside the battery and down the left foot compartment, all good.

That was pretty much what I could do yesterday with limited tools.

Today I disconnected the injector and despite fuel pressure it wouldn't squirt. Giving it 12v directly from the battery worked until the pressure disappeared (did this with the ignition off, therefore no lasting pressure).

I measured the voltage to the injector, key on 1.91v. With starter on, also 1.91v...

I'm terrible with electrics, I can have the obvious fault right before me and still not seeing it...
Does anybody here have other suggestions I can try or even know what's wrong?

Anything and everything appreciated mates!

I'm not exactly sure what the injector waveform looks like but I'm fairly certain it's a string of pulses. Your DC voltmeter won't give you an accurate measurement; your 1.9v may very well represent good 12 volt injector pulses. The better way to test the injector is to pull it out and see if it sprays fuel.

Also, I don't think that the fuel pressure is connected to the Check Engine Light system. (I don't think there's a fuel pressure sensor, but I could be mistaken.) Again, pulling the injector would be a good test.

Check engine light usually points to oxygen sensor problem

The injector (along with the fuel pump and coil) gets a constant 12V. It's the ECU that grounds it to squirt fuel. If you're measuring across the connector to it, then as above it gets pulses to ground, so you can't get a useful DC reading.

The usual thing with the injectors is a crack where the connector joins, so no good connection.

As stated above, It does spray fuel when given 12v directly.
Seems to me like the ECU doesn't deliver the right voltage, but why?

I measured the +/- on the connector itself when I read 1.91v... Should I instead ground to the chassis for the correct value?

The bike is still staying where it broke down so I don't have the possibility to try things in a jiff...

I think you're gonna need a oscilloscope to verify it is getting the proper pulsing signal

Doing a read between both points in the connector is not correct and the read can be anything.

The first test, constant +12V to chassis, to be sure that the constant +12v exist. If exist you need to go to a more deep test as the connector not doing a good connection, or a broken cable between the ECU and the connector, etc.

It is not common that the ECU don't send injector signal, as it is the basic /more important function.

And yes, the correct way to know if injectors are receiving signal is using a oscilloscope.

Considering the circumstances, I'd highly consider just getting a new injector and roll the dice. 50/50 chance it is just the injector at fault

Hello guys and sorry for the absence, I sunburned myself badly and couldn't do anything this two last days...

After rereading the posts here I want to one more time say that the injector is already tested and I know it works.

Later today I'm going to measure the voltage on the injector but ground to the chassis as suggested, posting the result here...

I been thinking making a jumper cable and feed the injector with 12v, hoping that the minus still will regulate the pulsing... Just so I can drive it home...

Thank to you all for taking your time!

Remeasured the injector, this time grounding to the chassis, 2.022v on the multimeter... Cranking the engine shows 1.9v again...

Didn't try jumping with the cable mentioned above since I didn't have time to make one, maybe today.

Just taking voltage readings is almost useless.

The ECU is using PWM (pulse width modulation), hence the need for a oscilloscope to see what type of waveform pattern the bike's ECU is producing.

Once the ECU is known to be good, then it is just a matter of either bad ground or bad injector or both.

You only gave one reading - what did the other wire show?
You should have constant 12V one side, the other will just be pulses to ground - which might not show as anything meaningful.

The plus wire to the injector shows max 2v grounded to the chassis/battery.
The minus to the injector pulses so rapid it is not possible to make sense of any reading...

If you have only 2v in the + grounded to chassis is a good guide for the problem. Maybe a wire broken and the injector is not receiving the full voltage?

I hope that's with the meter grounded, not the wire itself? You description is ambiguous...

I have the injector connector disconnected from the injector so I see the two leads.
With my multimeter reading Volt I have the black one connected on the battery minus.
The red one on the disconnected connector reading the plus wire.
Total Volt ist 2V with ignition on, same when cranking...
Putting the red on on the connectors minus lead gives erratic numbers...

Yes, my thought too! That's why I wrote about the jumper cable above.
However, the way it just died on me ant that it still produces some volt make me doubt that...

But again... Me and electricity...

You have identified the problem - no 12V at the injector with ignition on.

Now check at the 'injection loads' relay. That should have 12V on the red/white wire (ignition switched to coil) and grey/black wire (fed permanent 12V from fuse 5). The black/violet wire gets grounded by the ECU to enable the relay, and the black/green wire is the output fed to the ignition coil, fuel pump and injector. That should read 12V with ignition on.

All measured w.r.t. frame.

wiring diagram at: https://manuals.wotmeworry.org.uk/Piaggio/Piaggio%20MP3/MP3%20400/

Wow, thank you mate!

I have to find where this relay is located on an 2008. If a relay is involved I'll bet it's the relay itself that needs replacement...

Bad weather in northern Germany today, I might have to wait until tomorrow...

You gave me hope mate, thank you dearly!

Did you find the problem? Thinking on others that can have similar trouble

I was there the day before yesterday, the battery has probably gone low over the X days it's standing there and my trying to start it back then.
I couldn't get the motor to turn around, long beep and the red tilt lamp is blinking... I need to get it home first of all and I'll try a few things after I charge the battery....

Sorry for the bad updates but rest assure, I'm not one of those who just disappears, I'll update the lot of my journey here.

Hi guys, a small update...

Was supposed to get help to get the bike home on a trailer this weekend, the dude got drunk instead...

I found the reason why my tilt locking system got pearshaped, it was the fuses beside the battery... I made a search and this thread solved that problem:
REd tilt lock flashes, no beeps or horn, wont start or tilt

How ever, I still can't crank the bike. Swapped the battery for a fully charged one, nothing. I noticed that I have the red antithieft lamp constant on since last time... See the pic.

If I don't get it home I won't be able to do much more where it stands right now, I need to strip the tupperware I think...

Before removing the bodywork take a close look at the starter relay and its integrated fuse

If the antitheft alarm light does not go out then you have a immobilizer problem or the aerial is not recognizing the key transponder

Great... and this is nothing I can solve myself I guess? I only have this one key ...

If it's the antenna that's damaged (it happened to me twice with the MP3 250), the only solution is to replace it.

The good thing (after the bad thing about its high price) is that you can unplug the old one and plug in the new one, and that's it. No programming, scanner, dealer service, or anything like that required. But to get to it, you have to disassemble all the parts surrounding the switch.

Hallo everyone, a small but positive update. Today all the surrounding electrical problems disappeared , I'm back to the original one, the low voltage to the injector. And this time I won't let the battery drain...

Don't know what happened, maybe the charged battery needed some time to tell the ECU that all is fine...

I'll try feeding 12v directly to the injector asap, maybe I all of a sudden will be able to drive it home...

A big Thank You to all of You for giving me hope!

Errr, yeah ... sure. The Italians may have invented electricity, but they mastered the art of electrical malfunction

I don't think the Japanese lay awake at night worrying about Italian dependability and reliability