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Thread: Help! K75 has no acceleration

  1. #1
    SweetT
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    Angry Help! K75 has no acceleration

    I was riding home tonight when I had to ride over some rough pavement. I didn't think it was unusually bad, but immediatly my engine had no power to accelerate. It idles smooth and starts fine, but when I try to pull away from a stop sign I get little help from the engine. If I open the throttle about halfway the engine revs and power drop and I can hear a grinding noise coming from the engine (but only when the throttle is opened). When I close the throttle the bike gets a little bit more power as the throttle closes (less than 1/4 open) and when the throttle is completely closed (after having just been opened) the engine will backfire. The way I got home was by opening the throttle about halfway and then slowly rolling off until I found the point were the engine would slowly build up power, which was about 1/4 open or less.
    Is this a fuel/air mixing problem? A valve problem? Timing problem?
    Please help me out here cause I'm at a loss.

    Thanks,
    Tarren Shaw

  2. #2
    SweetT
    Guest

    K-Bike, Heal thyself!

    In the amount of time it took me to type up the porblems with my engine, read the trouble shooting section of my haynes manual and scratch my head, the bike "fixed" itself. I went back outside to start it up and it had the same problem for about three minutes, then it started running fine. I took it for a lil ride and it has plenty of getup-n-go! I guess some air was jostled into the fuel line? Whatever it was its gone now, so I hope it doesn't come back.
    But if you have any idea what may have caused this problem, please let me know. That way if it happens again, I'll know how to fix it.

    Tarren Shaw

  3. #3
    rabid reader dbrick's Avatar
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    I've never heard of air being "jostled into the fuel line," especially since if that were the case, you'd have seen the resultant fuel leak, because the entire fuel system is under pressure.

    No power/won't take throttle could be caused by an intermittent leak in the rubber in-tank fuel line (downstream of the fuel pump), or by an intermittent blockage in the fuel filter.

    I'd go into the tank, change the rubber lines inside, and change the fuel filter.
    David Brick
    Santa Cruz CA
    2007 R1200R

  4. #4
    SweetT
    Guest
    david,
    I just replaced the fuel filter about 3k mi ago, but the fuel line inside the tank may be old and leaky. I'll check it later today. This is the first fuel injected bike I've had to work on so I'm not used to something like fuel pressure problems being an issue. I dont think I ever would have thought to check the fuel line inside the tank.

    Tarren

  5. #5
    rabid reader dbrick's Avatar
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    Hi Tarren,

    Bits from a failing rubber hose may have clogged even the new filter you just installed. I think (it's been a long time since I've been in a K bike tank) there may be some other soft stuff in there (a "sock" sort of thing which covers the fuel intake into the pump, perhaps) which could also have clogged the filter.

    I'd do the whole job: pull the pump and filter, then remove and drain the tank. This will make sure that there's no water in there (which will clog the filter), and no bits of rubber or other stuff (see first paragraph) either. Then replace the rubber lines and other soft bits.

    -David
    David Brick
    Santa Cruz CA
    2007 R1200R

  6. #6
    Cal
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    Tarren,

    Don't forget to check the rubber mount for your fuel pump. When was the last time it was replaced?

    Cal Garcia
    Sarasota, Fl

  7. #7
    A bozo on the bus deilenberger's Avatar
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    Re: Help! K75 has no acceleration

    Originally posted by Tarren Shaw
    I was riding home tonight when I had to ride over some rough pavement. I didn't think it was unusually bad, but immediatly my engine had no power to accelerate. It idles smooth and starts fine, but when I try to pull away from a stop sign I get little help from the engine. If I open the throttle about halfway the engine revs and power drop and I can hear a grinding noise coming from the engine (but only when the throttle is opened). When I close the throttle the bike gets a little bit more power as the throttle closes (less than 1/4 open) and when the throttle is completely closed (after having just been opened) the engine will backfire. The way I got home was by opening the throttle about halfway and then slowly rolling off until I found the point were the engine would slowly build up power, which was about 1/4 open or less.
    Is this a fuel/air mixing problem? A valve problem? Timing problem?
    Please help me out here cause I'm at a loss.

    Thanks,
    Tarren Shaw
    Note - I've read your posting where the bike started running OK again, so I'm basing my reply on that fact.

    Also - using some paragraphs (look for the ENTER key on your keyboard,) makes things lots easier to read and understand. Good replies come to those who make things easier to understand.

    OK - on to your problem:

    First rule of K bike troubleshooting: Change the fuel filter, but people have told you this already. In this case - it doesn't sound like a fuel filter problem.

    They've also suggested checking the in-tank hoses - in this case, it doesn't sound like a hose problem.

    The reason I'm discounting these possibilities (although it's worth checking them) is - the problem went away. Fuel problems usually don't go away... they just get worse. Hoses don't unsplit, and filters don't unclog... but here is one possibility fuel related that I'll pass on.

    What you have is an intermittent problem - which usually indicates an electrical problem. The fact that the bike ran OK after sitting for a while indicates the problem may have a thermal component - gets worse when it's hot.

    Things that should be checked on your K bike:
    ============================================

    1. Computer - the silver box under the seat. You want to remove it (do NOT short it to the + battery cable). This can be done without disconnecting the big connector if you snip any tie-downs holding the large wire going into the connector off the frame downtubes.

    Remove it - then look for the spring latch assembly (located at the wire end) that holds the connector in. Move the latch, pivot the connector out and off - then pivot it back on until the latch clicks.

    A dirty of loose FI computer connector can cause the symptoms you saw.

    BTW - I have *NEVER* found a validated case of failure for K bike L-Jetronic computers - which is what you have. I have seen more than once a loose or dirty connector. People have thought they had a bad computer, 'cause they swapped it and the bike seemed fixed. It seemed equally fixed when they put back their own computer since the fault was a poorly seated or dirty connector, fixed when they did the swap.

    2. Ignition switch. A dirty ignition switch can cause foul running on a K bike. Turn the switch to ON, (don't start the engine) and observe the lights on the dash. Wiggle the key without moving it from the ON positon. If the lights get brighter or darker - the switch needs cleaning.

    3. Bad plug wires - and unfortunately, K75 wires can't really be tested with an ohmmeter (they have an air-gap in them). Usual test is by replacement, which is pretty darn expensive. My test is to use a timing light with an inductive pickup, move the pickup from one wire to another as the engine is missing. If one wire makes the timing light flash differently than the two other ones - that's the one to suspect.

    4. Coils - they're under the black plastic cover on the left side behind the engine. Take off the cover - make certain the plug wires are fully inserted in the coil towers and check the wires going to the connectors on the bottom of the coils. You might also clean off the top of the coil while you have the cover off.

    5. Bad plugs - rare on a K75 since the plugs (the stock Bosch ones) pretty much last forever*.. and I don't think this would give a thermal failure. (* = more than 30k miles on most K's)

    6. Bad HES sensor. The Hall-Effect-Sensor is what tells the engine when to fire the coils. Your K75 has two of them. If one of the fails - you will have the running problem you describe. They tend to start to go bad in a thermal manner - failing when the bike gets warm, working OK when it cools off.

    The test for this is the "Dunkle Test" - it involves removing the cover over the HES sensors (the T shaped cover on the front of the engine - right side) and then starting the engine and letting it run for a few minutes.

    As it's running - point a hair-dryer at the aluminum plate the HES's are mounted on (they face inwards towards the engine).. if the engine starts running rough or stops running - there is a good chance the HES is bad.

    Now - turn the heat off on the hair-dryer and point it at the backing plate - you want to cool it off. If the bike runs OK when the plate is cooled off - the HES is likely going bad.

    Since the HES is expensive - you may want to check it a few times or have a dealer check it for you.

    7. Bad ignition module - I've never actually seen a bad one, but I guess it could happen.

    8. The one exception to a fuel related failure (although I'd expect total lack of running, not reduced power) is the connector going to the fuel pump or the wiring in the tank for the fuel pump. If you're not comfortable messing with electricity in the fuel - you don't want to try to test this..

    First make sure the 4 pin connector going to the tank is connected firmly - it's on the right side of the bike - usually under the battery sidecover. Look for the wire that goes into the tank.. and make sure the connector on it is tight. DO NOT confuse this connector with the nearby identical connector for the gear-indicator (one of BMW's bigger blunders) - on most bikes the pump connector has a tag attached to it indicating what it is. But not ALL have the tag. ONLY disconnect one connector at a time if you're in doubt.

    If this didn't help, then:

    Again - the bike has to be running crappy when you do the test:

    Use a voltmeter VERY carefully to check the voltage getting to the fuel pump. You want to do this with the pump connections covered with fuel (a spark can't do bad things if has no oxygen).

    With the bike running - I'd expect to see roughly battery voltage at the fuel pump connectors. Minus ~ 0.5V wouldn't worry me - more than that I'd be looking for why.

    If you blow yourself and the bike and the nearby nursery school up doing this test - you did it on your own... The MOA and myself take no responsibility (see my sig) for blowing things up real good.

    ============================================

    Thats the elementary tests you can do with basic tools and household stuff. If this doesn't cure the problem - more advanced troubleshooting has to be done..

    Big problem you have - it's running OK at the moment. It's LOTS easier to find a problem if the problem stays broken.

    FWIW - I have never seen failure #3, 4, 5 or 7. I've personally seen #1, #2 and have heard of #6 and #8.

    ============================================


    HTH,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  8. #8
    I am here to serve you. hankb's Avatar
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    Re: Re: Help! K75 has no acceleration

    Originally posted by deilenberger

    and filters don't unclog...
    There is one exception to this rule but I don't know if it applies in this situation. Many cars have a strainer on the fuel pickup. If there is a lot of debris in the tank, it can pick up on the strainer until fuel starvation occurs. If you shut the vehicle off long enough to depressurize the fuel system, the crud can fall off and eliminate the problem until the crud picks up again. The problem usually gets worse when the fuel level is low. It usually does not take a sudden jar to occur.

    I personally worked on a car that would stall out completely and not restart unless it sat for about 5 minutes. I got *real* lucky when it did this as I pulled it onto my repair rack. I pulled the fuel pickup, which had a rubber hose on the end. Below it, on the bottom of the tank, was a small piece of paper. I removed the paper and the problem was solved.

    I have no idea if there is any possibility that this could happen on a K75 fuel pickup. I don't know if there is any kind or strainer that could plug up. I have heard that the fuel pick up is in a well that tends to catch any non-floating crap in the tank.

    HTH,
    hank
    Hank Barta
    K1200RS, R100R/Velorex 700
    Beautiful Sunny Winfield, IL

  9. #9
    A bozo on the bus deilenberger's Avatar
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    Re: Re: Re: Help! K75 has no acceleration

    Originally posted by HankB
    There is one exception to this rule but I don't know if it applies in this situation. Many cars have a strainer on the fuel pickup. If there is a lot of debris in the tank, it can pick up on the strainer until fuel starvation occurs. If you shut the vehicle off long enough to depressurize the fuel system, the crud can fall off and eliminate the problem until the crud picks up again. The problem usually gets worse when the fuel level is low. It usually does not take a sudden jar to occur.

    I personally worked on a car that would stall out completely and not restart unless it sat for about 5 minutes. I got *real* lucky when it did this as I pulled it onto my repair rack. I pulled the fuel pickup, which had a rubber hose on the end. Below it, on the bottom of the tank, was a small piece of paper. I removed the paper and the problem was solved.

    I have no idea if there is any possibility that this could happen on a K75 fuel pickup. I don't know if there is any kind or strainer that could plug up. I have heard that the fuel pick up is in a well that tends to catch any non-floating crap in the tank.

    HTH,
    hank
    There is a strainer on the input side of the fuel-pump - but it's an awfully big one (the diameter of the pump and about 1" high) so I doubt if something could cause a transient clogging..

    One other possibility just occurred to me - which is water in the fuel. That could cause these symptoms, and he might have sucked it all through the FI system..

    Best,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  10. #10
    SweetT
    Guest
    I rode to my parents house this weekend for Mothers day (about 110 mi nonstop each way) and I had no problems at all with the bike. This makes me think that my earlier problem was not heat related. I've also jiggled my electrical connections and that made no difference to how the bike ran. During the winter I unplugged every wire, cleaned the contacts and applied dielectric grease, and plugged everything back in.

    Its possible that water in the fuel could be the culprit as my bike was throughly rained on about a week previous. I'll be sure to clean out the tank and replace any rubber hoses and seals before I head out to spokane.
    Thanks for all your help!

    Tarren Shaw
    Stillwater, OK
    PhD to Be

  11. #11
    A bozo on the bus deilenberger's Avatar
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    Originally posted by Tarren Shaw
    I rode to my parents house this weekend for Mothers day (about 110 mi nonstop each way) and I had no problems at all with the bike. This makes me think that my earlier problem was not heat related. I've also jiggled my electrical connections and that made no difference to how the bike ran. During the winter I unplugged every wire, cleaned the contacts and applied dielectric grease, and plugged everything back in.

    Its possible that water in the fuel could be the culprit as my bike was throughly rained on about a week previous. I'll be sure to clean out the tank and replace any rubber hoses and seals before I head out to spokane.
    Thanks for all your help!

    Tarren Shaw
    Stillwater, OK
    PhD to Be
    Tarren - glad to hear it's running well. It may have just been a slug of water. Some dry-gas might be used to make sure it's all out of the tank. K bike tanks corrode along the bottom seal when they get water in them..

    As far as the electrical system - I am not a fan of "dielectric grease" - think on what the name "dielectric" means - it means non-conductive. If you use it - you're counting on mechanical pressure and friction to cut through it to make a sound electrical connection.

    BMW dosen't use and dosen't recommend the use of dielectric grease on any of it's vehicles that I know of. I think they might suspect that motorcycle electrical connectors might be exposed to the elements - but I think they'd rather have that then a high-resistance path caused by a layer of insulatiing grease.

    When I installed a new wiring harness on my K a year ago (long story on why..) I used an "electrical contact enhancer" fluid on all the contacts. Many of the electrical connections on a K bike are low voltage, low current connections. Adding resistance to the connection by using a dielectric grease can cause problems.

    The contact enhancer I used is one recommended by BMW for use on their automobiles. It is very expensive, but also very good.

    You can buy it at your local NAPA autoparts store - it's their part number: ECHCE1, and it lists for $61.49 for about 10cc's of it. That doesn't sound like much - but it is used sparingly, and after doing my entire harness - I couldn't really see any reduction in the level in the little tube it comes in. My local NAPA store felt sorry for me (so little for so much) so they sold it to me for around $40.00

    Best,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  12. #12
    rabid reader dbrick's Avatar
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    Tarren,

    I've been watching your discussion with Don E., and I certainly agree with the points he's made.

    I'd like to offer in addition that folks have reported that water contamination can plug the fuel filter. Apparently the one in your machine isn't plugged now...but given its relatively minor cost, that a plugged filter will stop the bike, and that you're going to be in there anyway, another prophylactic filter change seems a good idea.

    -David
    David Brick
    Santa Cruz CA
    2007 R1200R

  13. #13
    SweetT
    Guest
    Thanks Guys,
    I'll order a new filter in the near future.

    But about the dielectric grease, I was under the impression that it helped conductivity, kept out moisture and dirt, etc. Why else would it be recommended for use on spark plugs, and engine condensors? These are places where you need a lot of current.


    Thanks again!

    Tarren Shaw

  14. #14
    A bozo on the bus deilenberger's Avatar
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    Originally posted by Tarren Shaw
    Thanks Guys,
    I'll order a new filter in the near future.

    But about the dielectric grease, I was under the impression that it helped conductivity, kept out moisture and dirt, etc. Why else would it be recommended for use on spark plugs, and engine condensors? These are places where you need a lot of current.


    Thanks again!

    Tarren Shaw
    That's kinda a common misconception. Again - think about the name "dielectric"

    Here's a link to a dictionary definition: http://www.hyperdictionary.com/dictionary/dielectric

    You'll note that synonyms are: insulator, nonconductor

    As far as spark plugs and engine condensors (what are engine condensors?)

    Spark plugs carry almost no current, but very high voltages. Dielectric grease is sometimes used on the outside of ignition wires in an attempt to make them more resistant to leaking of the high-voltage pulses to ground or another wire. This is usually a bad idea since wires that allow "crossover" or pass-through to ground are bad wires and should be replaced. The dielectric grease applied to them is a short term fix that doesn't address the cause of the problem.

    Dielectric grease will keep moisture and to some extent dirt out of electrical connections. And it may work OK in connectors where there is sufficient mechanical contact between the connectors to force through the dielectric and make a metal to metal connection.

    It's a decidedly bad idea to use it on low voltage, low current connections.. things on the K bikes like ABS sensors, speedo sender connections, connections inside the instrument pod, the Hall-Effect-Sensor connections, and probably a few dozen other places that didn't pop into my mind.

    The big thing to understand - dielectric compounds by design are insulators and they lessen conductivity.. so they should be used only in places where specified.

    In this case - AFAIK - BMW doesn't specify their use on any connector on a BMW motorcycle (or BMW car also), so I wouldn't use the stuff.

    They do recommend the use of Stabilant 22 (the stuff I mentioned above with a NAPA part number) in a lot of these connectors on the cars - and may well include it in the service instructions for these type of connectors and signal paths on the bikes.

    Here is the home page for Stabilant: http://www.stabilant.com/

    Reading the application notes might yield some useful info.

    One on use in auto applications can be found at: http://www.stabilant.com/appnt20h.htm

    Best and hope that clears up the confusion,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  15. #15
    SweetT
    Guest

    I had no idea

    Well thanks for setting me straight about dielectric grease. And here this whole time I thought I was doing something good for my bike! Is there an easy way to remove the grease I've put in the connectors?

    Tarren Shaw

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