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Electronic fuel injection question

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by redviffer, Dec 24, 2007.

  1. If you are running a bike with electronic fuel injection and you run empty as in completely dry and you get an air bubble in the fuel system how big a problem is this?

    Would you simply just fill up and the problem is solved or would you have to completely drain the fuel lines and system to get rid of that bubble?

    I'm asking because if it was an absolute worst case scenario and you were going to run out of fuel would you not just turn the bike off at the last possible moment to avoid damage or problems or would you let it run completely dry secure in the knowledge that all will be fine?

  2. I can't answer the technical part, but surely with a fuel guage, and some knowledge of the bike's behaviour, there would be no reason apart from laziness or stupidity for running out of fuel completely??? (Not saying YOU'RE stupid, just that you shouldn't under any circumstances run out of fuel completely...)
  3. any injection system post 1990ish will be self-priming.
    no worries
  4. Unless your bike is a diesel and has no self bleeding injectors, just put fuel in and turn the key on and off a couple of times, you will likely hear the pump pushing fuel up to the injector rail, then hit the starter, and off you go.
  5. You're assuming that all bikes have accurate fuel gauges.

    What about those who don't?

    For example, we're riding from Mt Hotham into Bright. Mate's TL1000 is low on fuel. Harrietville's servo was closed. He ran out near the Tawonga Pass turnoff. We rode into Bright and got a fuel can for him. He emptied it into the tank. Turned it on and hit the starter. It fired instantly.
  6. Being a bit on the forgetful side, I've run several EFI vehicles, cars and bikes, completely dry. They've all fired up fine as soon as the tank's been refilled.

    An EFI system isn't like an old-school, mechanically injected diesel that would need bleeding after a dry tank incident. Once the tank is filled I can't see any reason why any modern system shouldn't self prime.

    One possible undesirable side effect might be to fill your fuel filter up with crud if there's much grot in the bottom of your tank. Hasn't happened to me yet though.
  7. You're assuming that all bikes have accurate fuel gauges.

    What about those who don't?

    For example, we're riding from Mt Hotham into Bright. Mate's TL1000 is low on fuel. Harrietville's servo was closed. He ran out near the Tawonga Pass turnoff. We rode into Bright and got a fuel can for him. He emptied it into the tank. Turned it on and hit the starter. It fired instantly.[/quote]

    My point here exactly, fuel gauges aren't as accurate on bikes as they are on cars either are distance to empty readouts. Now you guys are correct in saying it would be out of lazzines or stupidity if i let it run totally dry. However let me explain my situation here:

    I had a VFR800 and used to keep a small jerry can in my ventura rack/bag for when going on really long runs and not being familiar with the territory i was covering. I knew that if i presumed there was another fuel stop and there turned out not to be i could safely say that at 350km to a tank I'm pretty much bone dry and could use my 10L jerry to get another 175km of range worst case.

    I now have a ZX-14 and have done stuff all K's on it. I was doing the Canberra-Batemans Bay-Nowra and return run the other day on it. My 'distance to empty' readout was at about 70km whilst cruising at 100km/h and i had no reason to not trust it as it had dropped at a fairly constant rate in relation to the fuel guage readout. All of a sudden it swithed to flashing empty at me. I had done 300km and wasn't sure how close to fuel i was, I also haven't put luggage loading options on the bike yet and wasn't carrying extra juice. By the manual when she flashs empty at you you have about 4.1L of fuel from memory, the VFR was 3.6L.

    Some time next year after i have fitted the bike with a few bits and pieces to make touring a little more comfy, I plan to ride from Canberra to Perth and back. I'll have plenty of room for luggage and extra fuel but was concerned that if i misscalculated and it ran dry that i would risk damage or problems with the technological masterpiece that is the ZX-14's motor.

    It hadn't even had its 1000km service when i nearly ran out and doing something like that so early in the engines life had me worried, lucky there was no real risk and it didn't happen but it got me thinking about the possible consequences had it had happened.

    Thanks for clearing it up for me guys.
  8. Think about it. What could possibly go wrong if it DID run out of fuel? The fuel pump runs dry, perhaps. But it's only momentarily.

    If the fuel pump was that delicate that running it dry, even momentarily, would stuff it up, then it has no place being in service. Otherwise, normal operation would see it wear out really quickly, presumably.

    And they're not cheap, either, if they do stuff up.

    What else could go wrong? Injectors? If so, how? Again, remember that as soon as they stop injecting, the engine stops operating. Sort of like when you turn the ignition off, huh?

    Whatever, you've nothing to fear but the fear of pushing it when it does run out (or leaving it unattended while you go for a walk to get juice).

    THAT is my biggest worry, not what it'll do the engine...
  9. About the only cause for concern is if you continually run your bike with a very low fuel level. In tank pumps use the fuel to keep themselves cool. No idea how long you would have to run it to cause any problems though :?
  10. If it runs out its all good.. No problems will occur..

    Although the gauge is fairly accurate, have had mine down to 30k till empty..
  11. Thanks Mjt57 and others for clearing it up, i guess i didn't really think that one through and as you might have guessed I have very very little mechanical knowlege especially when it comes to bikes.

    Still I thought when the answer doesn't come to me from common sense or a lack there of then i thought it best to ask, thanks to everyone who replied
  12. Actually it was a very legitimate question.

    Very early fuel injection systems could be damaged by running out of fuel, and it could be very expensive to fix them. My father had to explain to some very unhappy Mercedes Benz owners why their very expensive car detroyed components when they ran ot of fuel. He used to tell them all not to run out of fuel, after one incident.

    As Roarin said, in-tank pumps use the fuel for cooling, and don't like running dry for an extended period. Early Mercedes Benz would keep running the pump if they ran out of fuel, and the driver left the ignition on, as the pump was trying to build fuel pressure, and didn't have a cutout.

    That has been fixed in modern systems, with pressure sensors and cutouts.

    Also, very early fuel injectors, if run dry, could effectively destroy themselves because they had no back pressure from the fuel they were trying to push. The plunger would shoot like a bullet, and jam the injector, and they would overheat. If a driver kept cranking the engine trying to fire it up, the injectors kept firing dry, and they suffered a catastrophic failure.

    That also has been fixed in modern systems, as Joel said, with self priming systems.

    So my Dad comes home from work one day, having been chewed out by a new Mercedes owner, who ran out of fuel, kept trying to start the car, then left the ignition on while some assistance, in the form of fuel, was sought. When the fuel arrived, the car still wouldn't start. On towing back to the dealer, it was found several injectors, and the fuel pump were buggered. Now is that warranty sir, or operator stupidity?

    Not to worry with a modern bike though.
  13. Yes the old injection systems used to use the fuel to keep them cool, and when they ran out of fuel they would cook the injectors.. :shock:
  14. How could this occur? If the engine runs out of fuel it stops. If it's stopped there is no heat being generated. Conversely, when you stop an engine intentionally, the same thing occurs.

    I personally think that this one belongs on snopes.com
  15. Why not the Department of Fair Trading???

    Actually, he's right in that some major diesel engine makers (Detroit for one) absolutely required you to never run below 1/4 fuel as a safety factor, because they use the fuel for cooling, as well as for fuel.

    I'm sure Merc, being an innovator, could have used a system in the early days with similar requirements. It's not an issue with petrol engines these days.

    BTW petrol engines are low pressure injection systems (under 100 PSI) while diesels use high pressure injection (even older ones well over 1000 PSI) Modern commmon rail diesel injector engines are running around 25,000 PSI at the injector.


    Trevor G
  16. Read my post above Marty, and you'll find out how it could occur, on early EFI systems.