I have a question for you all. Is it possible to push start an EFI bike?

I was at the RENO Street Vibrations looking out my Hotel window on Sunday watching two guys pushing a Copper Top around the parking lot trying to push start it. I thought to myself. "You guys need to jump start it because it is EFI." Finally somebody stopped them and told them to push it over to a pick up truck and they jump started it.

I started thinking afterwards, If there is enough juice in the battery to spin up the Fuel pump, but not crank the engine, could you push start it?

Could you Push it, turn on the ignition so the fuel pump starts and then pop the clutch to spin the motor over. The crank sensor should fire the ignition and open the injectors...

I would try but it would take to much energy on my part.

 

I'd have to say maybe. If the bike has a cam position sensor to tell the ECM which cylinder is coming up to fire next, then push starting would be a possibility, assuming the battery has enough power left to run the fuel pump and coil.
On the other hand, if it does not have a cam sensor like the late model harley, the ignition system uses flywheel acceleration while cranking to determine which cylinder is
getting spark next. When using the starter motor, the engine will slow down as compression builds and speed up again once it gets past it. However when push starting the speed of the engine turning may be too consistent for the module to figure out which one to fire, and it won't fire the plug.

so, maybe... maybe not

Hogdoctor

 

I think EFI or not is irrelevant. So long as there's enough juice in the battery to provide excitation voltage to the alternator it should be push-start-able. If there's not enough juice in the battery for suitable excitation voltage, the alternator will never "start", so the engine won't either.

In terms of crank position, that's known precisely at all times and I wouldn't be surprised if the injector didn't spray half its fuel every revolution and the plug sparked every revolution such that physical timing based on which revolution is happening would be irrelevant.

 

I did not think the alternator would play into the equation. I thought the alternator just charges the battery. The battery feeds the coil.

You would be right on a magneto equipped bike because they do not rely on the battery.

 

It can be done. Did it last weekend for a girl whose Road King would barely turn over. 3 friends and I pushed it down the road, turned on the ignition, dumped the clutch in 3rd gear and viola, started right up.

 

I've had my '03 FLSTSi push started as well.

 

Glens sayz: "So long as there's enough juice in the battery to provide excitation voltage to the alternator it should be push-start-able."

The alternators are driven by permanent magnets, they do not need to be 'excited' to function. Besides, when push starting, you might get 200 rpm if you're lucky, not nearly enough for the charging system to make any significant contribution to the electrical needs.

Glens also sayz "In terms of crank position, that's known precisely at all times and I wouldn't be surprised if the injector didn't spray half its fuel every revolution and the plug sparked every revolution such that physical timing based on which revolution is happening would be irrelevant."

This is not the case with any of the HD EFI or any twin cam engines, they are all single fire systems, both ignition and injection. They do NOT however even have a cam sensor (at least not since '00), so they have to calculate the engine phase (ie cam position) by monitoring the AC pulse read off the notches in the flywheel edge, and the changes in flywheel speed as it hits compression on either cylinder.

Hogdoctor

 

Okay, permanent magnets obviate need for excitation. The ECU itself might could be powered-up by a couple hundred rpm, but the fuel pump certainly would not operate at that rate. It really boils down to whether the battery is dead / very nearly so or not at the time the push-start is attempted.

Not discounting the common confusion between just what the terms "single fire" and "dual fire" actually mean, but each cylinder having its own coil doesn't have to mean that the coil only fires on the compression stroke. Wasting a harmless spark on the exhaust stroke or a half-shot of fuel then (which itself wouldn't be wasted at any rate) is a lot simpler to implement than monitoring the acceleration rates of the crank speed pickup. Although this particular bit is not really pertinent to the discussion at hand, it's certainly just the type of stuff I like to know. Do you have any documentation sources you can divulge?

 

Glens sayz: "each cylinder having its own coil doesn't have to mean that the coil only fires on the compression stroke. Wasting a harmless spark on the exhaust stroke or a half-shot of fuel then (which itself wouldn't be wasted at any rate) is a lot simpler to implement than monitoring the acceleration rates of the crank speed pickup. "

The HD twin cam is a true single fire ignition and injection system. Nothing is wasted.
Besides, a half shot of fuel on the backside of a closed intake valve will quickly drop out of it's atomized state back into a dribble and not burn completely,, the EPA would never allow that. It's fine for Lucas injection, but not for the Harley.

While it's true that the ECM knows the position of the flywheel at all times, it does NOT have any direct knowledge of the camshaft's position without the cam sensor which was eliminated for several reasons. The engine has to figure it out when you start cranking the engine. If it cannot figure it out, then you get no spark. This is why if you pull the spark plugs on a twin cam and try to test the spark cranking the engine over, sometimes
you won't get any spark.. there's no compression so the module can't figure out which coil to fire. It is absolutely pertinent, because you might have the same situation when trying to push start a bike.

My sources? Many trips to Juneau ave in Milwaukee for factory training, Many years experience troubleshooting these systems for a living. Any documentation is classified and copyrighted, so I can't divulge any of it. You'll just have to trust me.

Hogdoctor

 

If you have enough juice in your battery to run the fuel pump, there's probably enough there to provide a spark or two, so I would think pushing starting is viable. If your battery is dead... no fuel pump - no fuel, no start.

Seems pretty straight forward to me.