87 K100RS START PROBLEM

[grant71]

HELLO. 1 ST OF ALL A HAPPY NEW YEAR TO EVERYONE.  my bike , this morning, fired and engine ran for a second  and then died. motor turns over vigorously but will not fire. walked away and used my other bike. When i tried to start my K100 afew hours later , same thing. motor runs for half a sec. i opened fuel tank filler and could  hear a faint whirr of pump also for a half sec when i pressed starter button. when i had  start problem  few months back pump was dead. i replaced fuel level sensor then a nd problem solved. any suggestions please. Grant

[Scott_]

1st thing I would try is to check, clean the multi-pin plug at the Jetronic controller as it controls both the fuel and spark.
BTDT with a fuel pump not running ended up being the connection at the computer not turning on the relay that drives the pump.

[K75RT Keith]

+1 to Scott's suggestion.  I'd also check the spark plugs for fouling and gap. 

[grant71]

further to my complaint, i removed fuel tank and tested the fuel pump taking current direct from battery. fuel pump works. connection under the seat needs to be tesred. now if memory serves me right , the green wire supplies power to fuel level sender which in turn feeds fuel pump. brown is  earth. what confuses me is the wires inside the tank from sender. the 2 wires are yellow and black connected to fuel pump. please corrct me if im wrong. thanks for your input and advice.

[Inge K.]

Yes, you're correct......outside the tank the green wire is power and the brown is ground.
Inside the tank the yellow wire is power (which Connects to the smallest dia. terminal at the pump)
and the black ground.

[grant71]

Thanks for yr input. Can a connect pos battery green wire neg to brown to activate fuel pump via fuel level sender ? My thought being that doing it directly will eliminate relays etc which may be faulty.

[Scott_]

Thanks for yr input. Can a connect pos battery green wire neg to brown to activate fuel pump via fuel level sender ? My thought being that doing it directly will eliminate relays etc which may be faulty.

If I understand what you are asking to do, you will only burn up the sender if not cause something much worse..........DON'T DO IT.

[grant71]

thanks for the warning. as i stated the fuel level sensor i had gave trouble . what i am looking to do is check the sender for function. shall i puttank etc back and try to start via starter button? the relay or whatever may be the problem 

[Inge K.]

Can a connect pos battery green wire neg to brown to activate fuel pump

Hmm.....I don't see why it should be a problem to test the fuel pump this way, as this is how the fuel pump
normaly is connected...........please explain, Scott.

The power won't be going via the level sensor, only through isolators in the baseplate to the sensor.

[Scott_]

Can a connect pos battery green wire neg to brown to activate fuel pump

Hmm.....I don't see why it should be a problem to test the fuel pump this way, as this is how the fuel pump
normaly is connected...........please explain, Scott.

The power won't be going via the level sensor, only through isolators in the baseplate to the sensor.

It sounded to me(his word usage, my misunderstanding) like he was going to send the power thru the level sender.........
connecting direct to the harness connector coming out of the tank is a good way to test, yes...you are correct there to bypass the relays.

[grant71]

Let me clarify my intention. Wires coming out of tank bottom viz. From fuel sensor . If i connect green ( im told is to fuel pump ) to batt pos and brown ( earth ) to batt neg. , will i destroy any component. My inexperienced thinking  tells me that if pump works then the sensor is ok.

[Scott_]

Let me clarify my intention. Wires coming out of tank bottom viz. From fuel sensor . If i connect green ( im told is to fuel pump ) to batt pos and brown ( earth ) to batt neg. , will i destroy any component. My inexperienced thinking  tells me that if pump works then the sensor is ok.

Yes, as long as you don't short anything out, you will be fine.....Green is pump + and the brown is pump -.

[grant71]

right. a few mins ago i connected batt pos to green and batt neg to brown. this via sensor.  fuel pump did NOT work. i removed sensor. everythingis intact and no wires adrift or broken. the sensor i bought about 6 mths ago as used part. sensor looks good.Question is : can an experienced person getthis device to work again. buying this part again is a mission ( comes from UK and is expensive . 

[rbm]

It sounds like your diagnosis is pointing to the sensor assembly as the culprit.  The terminal block on the base plate of the sensor is just there to make a fuel-tight transition between the wires on the outside of the tank and those on the inside.  Use a multimeter on the Ohm setting to measure continuity between the brown outside wire and black inside ring terminal.  Do the same for the White and Green wires.  If either shows discontinuity, then there may be a break in the wire.  This can most likely happen to the inside wires.  They are continuously immersed in fuel and can become brittle.  Replacing any wire is time consuming but not difficult.

[Scott_]

It sounds like your diagnosis is pointing to the sensor assembly as the culprit.  The terminal block on the base plate of the sensor is just there to make a fuel-tight transition between the wires on the outside of the tank and those on the inside.  Use a multimeter on the Ohm setting to measure continuity between the brown outside wire and black inside ring terminal.  Do the same for the White and Green wires.  If either shows discontinuity, then there may be a break in the wire.  This can most likely happen to the inside wires.  They are continuously immersed in fuel and can become brittle.  Replacing any wire is time consuming but not difficult.

So hit me over the head with a 4X4, I finally realize what your are dealing with...... Like RBM suggests, check the continuity of the individual wires, but I'd bet that one or 2 of them are bad in the "transition" (sealed) area of the assy. I have heard of others, though not many, that have had the wires break in this area and it is not repairable.
The only solution is to replace the entire sensor/float/wiring assy.

[grant71]

hi.this morning a  friend used his tester on the sensor. set the insrument on ohms and all the wires had continuity.  now do i look at relays for function? the fuses seem to be ok. a while ago i checked and cleaned the earth wire. your help is appreciated. btw. what is the significance of a red  and white bmw logo as opposed to the blue and white quadrants?

[pfls]

Have you checked to be sure that there is no fuel leak from the internal fuel hoses or filter? The fuel sender has nothing to do with the control of the pump, it is just for the fuel gauge. If your pump is running when you try to start the bike, it is getting power.

[Scott_]

right. a few mins ago i connected batt pos to green and batt neg to brown. this via sensor.  fuel pump did NOT work. i removed sensor. everythingis intact and no wires adrift or broken. the sensor i bought about 6 mths ago as used part. sensor looks good.Question is : can an experienced person getthis device to work again. buying this part again is a mission ( comes from UK and is expensive .

If connecting power direct to the harness and you have no pump, and you friend checked the wiring continuity with good results,
I'd suggest the next test would be to remove the pump and test it on a bench in some fresh air....(hint no gas fumes....) 

You may be having a pump starting to fail. 

[grant71]

As i wrote before the fuel pump when connected direct to the battery works well and petrol exits the pipe on left bottom of tank. No leaking internal hoses. What i ll do now is test for continuity from wires on batt side of tank connector to wires  to fuel pump terminals.

[grant71]

what i dont understand is how the green wire functions. this wire fires up the fuel pump via the fuel sensor. now the question is : does this green wire only come alive when a) the ignition key is turned on or b) when starter button is pressed. also is this wire only alive for a second or two to enrich cold start? i am totally confused. of course fuelpump must have constant feed of electricity.

[Inge K.]

The fuel pump get power for a couple of seconds when the starter button is pressed, and get continous power when the engine is turning (when the ignition ECU receive signal from the hall sensors.
The fuel injection relay deliver power to the fuel pump and other this and that in the FI system.
(injectors. AFM, TPS, FI ECU).
The FI relay get its signal from the ignition ECU at the ground side of the relay coil.

When you push the button, or the engine is turning...ignition ECU grounds the relay coil...the relay closing the contacts and deliver power to the fuel pump + this and that.

[K75RT Keith]

Possible the HES is going bad?

[Scott_]

Grant, if you energize the pump by directly powering the green wire from the battery, does the bike run if you turn the ing on and press the start switch?

If you are getting spark, and the engine runs this way, then at least you can rule out the HES sensors.

[grant71]

thanks for advice and input. i ll be putting pump back into the tank shortly and i ll try to start. btw. before i took pump out to test it there was spark at the plugs. can i deduce that this must be a fuel starvation problem?

[grant71]

i ve replaced the fuel pump into the tank. connected directly to the battery and pump works ok ( black wire is earth to larger of the 2 nuts on pump ?  polarity right? ). im going to connect the 4 wires under tank to see whether i have further continuity. please tell me where is the next connection point is, so to speak, so that i can test continuity. would it be from the fuses?