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K100-forum.com » Technical, repair and troubleshooting » Engine and transmission » update on the fuel pump saga

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1Back to top Go down   update on the fuel pump saga Empty update on the fuel pump saga Sun Jul 25, 2021 10:46 pm

Spexbike

Spexbike
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this is 1985 k100 rs. The bike ran about a week ago when I still had overheating problems.I got a new coolant sensor,new thermostat, a used cooling relay,removed the vacuum sensor and plugged the barb on cyl 1 on the throttle body.Bike cranks over but won't fire up w.No fuel getting to the fuel rail.open the tank ,took the fuel hose that goes to the top of the pump off the filter,pushed start... at this time I should have fuel squirting out of the hose,correct? but nothing.It's a new pump,it worked before. Even put the old cooling relay back in to make sure that is not the issue,but that shouldn't even have anything to do with the fuel pump,
 I checked all the fuses and turns out I don't get any power to the fuel pump fuse (fuse6),but I have power to the 4 pin plug,how does that make any sense? I checked the back of the fuse panel and it all looks fine.
 
fuse1  12.88V
Fuse2   6.5
Fuse3   11.66
Fuse4  0V
Fuse5  0V
Fuse6  0V
Fuse7  7.5V

4pin plug to tank:
green/white-brown/black 10.98V
green/white-brown/white 10.97V
green/white-brown 10.87
green/white-2nd brown 0.0V
This is with ignition turned on ,battery is holding a charge 12,7 V
I thought I was gonna jump the pump (just for a second to see if it is running) 
from right side of fuse 4 to left side fuse 6,but since I didn't have any power on the fuse locations,I didn't even try.
Put everything together after I pulled the fuel pump relay to inspect and clean contacts,pushed start 3-4 times and nothing,couldn't hear the new pump kicking in ,any advice is greatly appreciated,anyone savvy with this stuff? THANX A Bunch



Last edited by Spexbike on Mon Jul 26, 2021 5:45 am; edited 2 times in total

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2Back to top Go down   update on the fuel pump saga Empty No go Mon Jul 26, 2021 12:05 am

daveyson

daveyson
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Doesn't make sense unless the previous owner bypassed fuse six, if for example the fuse socket was failing. You might find an extra fuse inside the relay box with power from a  green/red wire previously at the fuse or from the fuel pump relay. Or follow the wiring back from the pump.

The fuel pump doesn't get power with the ignition on unless the start button is also pressed.

It could be the tank wiring that's bad.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

3Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 1:01 am

robmack

robmack
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If you do not have voltage at the supply side of Fuse 6 (Green/Red) with the ignition on, kill switch normal and start switch pressed, then there is a problem with the FI relay, pin 87.  Does the start motor crank the engine?

When you are measuring your fuse voltages, are you measuring on the supply side of each fuse relative to ground?  Or the output side relative to ground?

There are no wires of the colour brown/black and brown/white on the tank connector, unless there has been modification of the original wiring going on.  Can you confirm that?  You should be able to ignore the White and Yellow wires on the 4-pin fuel tank connector (harness side) as they have nothing to do with the fuel pump.  The only wires that matter for fuel delivery is Green/White and Brown.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

4Back to top Go down   update on the fuel pump saga Empty No go Mon Jul 26, 2021 1:50 am

daveyson

daveyson
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It's a safe bet this is an early version say like a 1984, since that has brown striped wires, where the later has yellow and white.

If the engine was cold on your last failed attempt to start it, and the temperature light was on, the computer could be tricked into believing the engine is overheated and deny an energized circuit to the pump. Something I've read, dunno how it's done though, I've read conflicting accounts.

I'd use a computer safe test light to see if you have power to 86 of the fuel pump relay with the ignition on, and earth to 85 with the start button pressed.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

5Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 5:32 am

Spexbike

Spexbike
active member
active member
daveyson wrote:Doesn't make sense unless the previous owner bypassed fuse six, if for example the fuse socket was failing. You might find an extra fuse inside the relay box with power from a  green/red wire previously at the fuse or from the fuel pump relay. Or follow the wiring back from the pump.

The fuel pump doesn't get power with the ignition on unless the start button is also pressed.

It could be the tank wiring that's bad.
no extra fuse in the relay box,power measurements were taking with just the ignition on,the bike was running before I redid the cooling system

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6Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 5:41 am

Spexbike

Spexbike
active member
active member
daveyson wrote:It's a safe bet this is an early version say like a 1984, since that has brown striped wires, where the later has yellow and white.

If the engine was cold on your last failed attempt to start it, and the temperature light was on, the computer could be tricked into believing the engine is overheated and deny an energized circuit to the pump. Something I've read, dunno how it's done though, I've read conflicting accounts.

I'd use a computer safe test light to see if you have power to 86 of the fuel pump relay with the ignition on, and earth to 85 with the start button pressed. 
Daveyson temp light was not on,engine cranks over.It's a 85



Last edited by Spexbike on Mon Jul 26, 2021 6:23 am; edited 4 times in total

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7Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 5:42 am

Spexbike

Spexbike
active member
active member
daveyson wrote:It's a safe bet this is an early version say like a 1984, since that has brown striped wires, where the later has yellow and white.

If the engine was cold on your last failed attempt to start it, and the temperature light was on, the computer could be tricked into believing the engine is overheated and deny an energized circuit to the pump. Something I've read, dunno how it's done though, I've read conflicting accounts.

I'd use a computer safe test light to see if you have power to 86 of the fuel pump relay with the ignition on, and earth to 85 with the start button pressed.
temp light has not been on

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8Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 5:49 am

Spexbike

Spexbike
active member
active member
robmack wrote:If you do not have voltage at the supply side of Fuse 6 (Green/Red) with the ignition on, kill switch normal and start switch pressed, then there is a problem with the FI relay, pin 87.  Does the start motor crank the engine?

When you are measuring your fuse voltages, are you measuring on the supply side of each fuse relative to ground?  Or the output side relative to ground?

There are no wires of the colour brown/black and brown/white on the tank connector, unless there has been modification of the original wiring going on.  Can you confirm that?  You should be able to ignore the White and Yellow wires on the 4-pin fuel tank connector (harness side) as they have nothing to do with the fuel pump.  The only wires that matter for fuel delivery is Green/White and Brown.
I am measuring with one of the leads of the volt meter on one side of the fuse socket  and the other lead on the other side of the fuse socket , not right?

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9Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 5:54 am

Spexbike

Spexbike
active member
active member
robmack wrote:If you do not have voltage at the supply side of Fuse 6 (Green/Red) with the ignition on, kill switch normal and start switch pressed, then there is a problem with the FI relay, pin 87.  Does the start motor crank the engine?

When you are measuring your fuse voltages, are you measuring on the supply side of each fuse relative to ground?  Or the output side relative to ground?

There are no wires of the colour brown/black and brown/white on the tank connector, unless there has been modification of the original wiring going on.  Can you confirm that?  You should be able to ignore the White and Yellow wires on the 4-pin fuel tank connector (harness side) as they have nothing to do with the fuel pump.  The only wires that matter for fuel delivery is Green/White and Bro

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10Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 9:37 am

robmack

robmack
Life time member
Life time member
Spexbike wrote:
Daveyson temp light was not on,engine cranks over.It's a 85
Ah, didn't think of that. I assumed it was a post-85 model.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

11Back to top Go down   update on the fuel pump saga Empty Re: update on the fuel pump saga Mon Jul 26, 2021 9:42 am

robmack

robmack
Life time member
Life time member
Spexbike wrote:I am measuring with one of the leads of the volt meter on one side of the fuse socket  and the other lead on the other side of the fuse socket , not right?
No, that's not right.  You'll want to measure everything relative to battery negative pole.  So, attach your black lead to either battery negative or the grounding point on the transmission.  Then take your measurements using the red lead on your test points.  Supply side of the fuses should be on the left when viewing the fuse panel.  Confirm this by referring to the schematic.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

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