Modern Vespa

EDIT 1 (15/07/2024) -- The problem has to do with the spark plug cap, if you want to skip to the end!

Hello. I did my search, and I know the most common causes (yes, there's fuel in her):
1. Battery (however, battery reads at 12.4 volts currently)
2. Spark plug
3. Issues in the fuel injection system/getting fuel to the engine
4. ECU

I was wondering if y'all might be able to help me figure out which of these four it MIGHT be given what happened (so as to reduce the time it takes me to troubleshoot it alone). Here was my ride today:

* Started at 7 AM, started right up.
* Drove about 200 yards, pulled up to a light, scooter stalled out.
* Restarted scoot. It stalls out.
(at this point, I thought the reason was overfilled gas tank)
* Restarted scoot at green light, then drove 90 miles.
* Filled with gas, started right up, drove another 90 miles (I did this 2 more times before I had the throttle issue))
* After approx 5 1/2 hours of riding, while traveling the highway at 70 mph, the throttle just stopped doing anything, and the scoot died.
* I pulled over. Scoot now turns over (and will turn over until I drain the battery) but will not start.
* 5 out of 6 bars of gas, according to the digital speedo, and this happened about 30 miles after fill up.

At no point did the scoot die when stopped at lights between highway exits and gas stations when tank was near empty. She seemed to be working normally after the first 2 engine shut offs in the AM, until the throttle issue.

Based on this behavior, is it possible to narrow down the 4 problems above as the "most likely" culprit? Or do I just need to work my way down the list to do the troubleshooting?

Thank you all so much!

Let's go step by step. We've ruled out the kill switch as it'll turn over.

First - do you hear the fuel pump 'whirr' for a couple of seconds when you first switch on?

Oh! I did see that in one of the other posts where the person with problems said he did that. I will try this and report back (it won't be until tomorrow - she's currently at a Subaru dealer 1 hour away so I have to rent a trailer and pick her up tomorrow). I'm grateful you're willing to help!

I have personally run across the following problems over the years:

1. Battery - A battery that spins over the motor may not provide enough voltage under load to satisfy the electronic fuel injector system. With a weak battery, the motor tends to cut out when stopped in traffic.

2. Charcoal canister flooded - Crack open the gas cap, listen for air to rush in or out, and then tighten the gas cap. Plug off the system and then cut a notch in the gas cap gasket to let the air in (likely illegal).

3. Very small amount of water in the gas - If you use gas that contains Ethanol, the alcohol will mix with any water droplets to produce a burnable liquid. Gas without Ethanol could use a small amount of fuel line antifreeze to accomplish this. No problem here anymore since all of our premium fuel now contains Ethanol.

Cheers and good luck,
Bob

Check the spark plug cap. Cap will wear over time and no longer make contact with plug.

We'll make a list of stuff to check once he's got hands-on again. Definitely one for that list though.

Yep!

Spark Plug next?

In this case, she died while actually under acceleration and had been running for a good 5 hours previously. I don't think the battery would cause it to die while actually driving, would it? I could see had I stopped and it died again, but here it died in motion. Removed and reinstalled gas cap. Still did not start. Don't want to cut a hole in the gasket if it's illegal.

Thank you for the ideas!

Check the throttle cables are still rotating the throttle body spindle, and ensure it rests at the idle position - and leave it there.

OK, next easy check is to see if fuel is getting into the cylinder. Does the exhaust smell of fuel when trying to start?

If unsure, you could either remove the injector (careful now, the wires are finicky) and see if there's a good spray when you turn it over. If so, put it back - if not report here.

Then remove the spark plug - is it wet with fuel? Before replacing, check the HT lead clips firmly to the tip of the plug and lay the plug on a metal part of the engine and see if there's a spark when you turn it over. If not, unscrew the HT lead from the cap and check there's copper there to make contact with the internal screw. Put your spare plug on, and test again for spark. If still no spark, unscrew the lead from the coil (fiddly!) and check that end. Check the coil for both correct primary and secondary resistances.

Common causes of no-start are broken wires into the injector or broken injector connector, and problems at the spark plug (cracked plug, corroded clip inside cap, HT lead frazzled).

I'll be back after I watch some vids so I can try what jimc recommends!

In this video (at the time it should start) Robot shows disconnecting the fuel line from the injector and then just turning the electrical on to see if the injector gets primed.

youtu.be/F_xDtly6KxU?si=bFVCLEpmhmbtXBGJ&t=285

So, is it enough to see if fuel is getting to the injector? Or am I testing the injector itself at this point?

Testing fuel delivery to injector AND the injector wiring AND the injector itself.

curious, what year?

2014
EDIT: I realized I didn't have the year in my info!

I would check the ignition system. First check the cap tightness as suggested. If good, pull the plug. If you don't want to do that, attach a spare plug to the cap and check for spark. Also, the scoot can die if the battery is failing to hold a charge because of 1) Old age/wonky battery or 2)it is being undercharged because of a failed regulator and/or lousy stator.

More evidence against a battery issue - When I first had issues and tried to get it started, after 7 or 8 seconds I would see the voltage drop on the USB port w/ battery volt display, as low as in the 9s, but would return to the 12s when I stopped cranking the starter.

Today I checked the battery at the terminals themselves with a multimeter (as opposed to a reading from my USB port w/ voltage display). Scoot has been sitting untouched for over 24 hours.

Today's multimeter reading: 12.70 volts. So I think it's holding OK charge (at the bottom end of "good") - at least enough to start her (and thus not a battery problem)?

Too hot out to do other recommended next steps (fuel system, spark plug). We're having a bit of a heat wave here in the US, and I do not do well in the heat.

Also, I may skip right to the spark plug (looking to see that it's wet with fuel). Scoot has 9500 miles, and when I looked at my receipt from the 6k/9k service I had concurrently (at 8700) at a "certified" vespa place, I don't think they replaced the spark plug.

I think I was getting only about 50 mpg on my long road trip, which could also be attributed to a "bad" spark plug from some of what I read on the interwebs.

You should check the battery voltage under load - as when the starter is working.

He did - down to the 9's after 7 or 8 seconds, which is fine.

Ooops! I missed that. Sorry.

Yeah, it's hot but it looks like the battery is not the problem. So check the cap and look for spark. Find some shade and a fan and you'll be alright.

That's the plan for the AM when it should be a little cooler.

good man.

Are the battery terminals tight? Might be worthwhile pulling off the battery terminals and cleaning them at this point.

So when one is willing to do the work, there is ONE (1) good thing about problems - it forces you to learn about your scoot.

I FOUND MY PROBLEM!

I went to pull the cap of the spark plug and I couldn't find it. After about 60 seconds of staring, I see this thing hanging down, holding on by a literal thread of wire. Once I went to lift it up, it came off. It looks like something in there overheated (caught on fire???) and melted? (I wonder if I was sloppy with the engine cleaner last time and that dissolved the cable - the black stuff feels like melted plastic.)

So, I just so happen to order the 90 degree cap from scooterwest Saturday night. I think that replaces this part?

How will I reconnect the wire to the new cap? I'm currently looking at an open ended stranded wire.

With it looking like that it's a wonder it ran at all. So it melted because it was hitting a hot engine part or a lot of resistance as the cap or wire was crapping out or not put on tightly or a combination of all of it. With a new wire and cap, you should be ready to go again. Good man for getting in there. Scooterpartsco will have the parts you need as I can almost guarantee you that you won't find the right cap anywhere else other than a Vespa dealership.

What does the coil look like? Is the wire fried all the way back to it? If so, you may need a coil as well.

do you mean the ignition coil?
I'm having trouble finding this part on the scooterwest interactive diagram. If it's the bit at the end of the wire that plugs into the spark plug cap, then it looks like it definitely needs replacing?

I expect you'll have to buy some new HT lead - available from every auto parts store, you don't have to buy the Piaggio stuff, unless it's more convenient to add it to an order.

The reason I expect you'll have to is because that wire will have to be cut back to a place where it's clean and unmolested, and then it'll be too short.

When you have a new length, unscrew the existing wire from the coil (fiddly!), cut the new wire to the same length the original was, screw the new wire onto the coil then screw the new cap onto the new wire.Hopefully you'll then be good to go!

It's a very good idea to keep a spare cap and a spare plug in your parts drawer, or even under the seat along with that spare exhaust bushing.

Yep. I ordered doubles this time. And don't have spare bushing! I guess I'll be adding that to my order as well.

I can't get a good picture of the wire, but I can see where the damage stops. I have about 6 inches of wire past where the wire is clipped into the wire holder on the front of the frame. I think I'm in a "I might reach but just barely."

That said: If I understand you correctly, I can't just splice in a new bit of wire to replace the damaged wire, but I need to actually replace the entire wire back to the ignition coil?

Do I need to disconnect the RED/positive from the battery before I do this work?

What is the part I will need to put on the end of the wire that connects to the spark plug cap -- is that the HT Coil - https://www.scooterwest.com/high-tension-coil-modern-vespa-58120r.html?

I've got the 90 degree plug and 2 spark plugs on order from scooterwest. They will hopefully get here this week. Going to follow jimc to replace/repair the wire and connector and then get back on the road!

EDIT: Do you know where scooterpartsco is located? It doesn't seem to say on their website.

Thank you for your help!

Watts, Oklahoma. Just across the state line from Fayetteville / Bentonville, Arkansas.

Right, no spicing. Install a new plug wire from the HT coil to the spark plug cap.

"Just barely" is no good for HT lead length. Go over a bump and you'll be repeating your current(!) problem.

Splicing HT leads is for those who know how to insulate 25kV. Don't do it - you could set fire to your scooter.

Don't disconnect the positive on the battery. ALWAYS disconnect the negative first (and replace last if you are indeed removing both). This is to prevent your wrench touching the positive and frame at the same time thereby releasing lots of smoke...

OK; AND should I disconnect the battery when I do this?

It's sufficient just to disconnect the negative, as above. Then the battery is isolated. Always worth doing when going near a vehicle's electrics.

I assume it's obvious how I attach the wire to the cap?
(parts should get here Wednesday; new lift gets here Thursday - it looks like it will be much easier to do the wiring from underneath)

It will be obvious - there's a screw thread attached to the coil, and a screw thread as part of the cap. You wind the wire onto the coil's screw, and the cap onto the wire. Use plenty of dielectric grease (auto section of your hardware store) at each end to keep moisture out and prevent it corroding another time.

Ensure when the cap is fitted onto the installed plug that the wire is well away from any hot engine bits, and cannot wave around to touch any.

well, scooter west sells a spark plug cable that's "plug and play," which I ordered since I had to order a few other things

Parts have arrived! Once the rain stops I can put my canopy up and get to work!

Going forward, it looks like I'll have to check this spark cable, as whatever I did seems to have melted half the plastic clip that's supposed to secure the cable to the plug! I can probably replace that too, but I'm not going to rush.