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post #1 of 6 (permalink) Old May 27th, 2013, 4:51 pm Thread Starter
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Help Electrical Problem

I have a 98 RS that keeps blowing the the fuse for the fuel pump. I have unplugged everything on that circuit. It blows everytime if the relay is plugged in. I have replaced the relay and still blows as soon as key is turned on. Any help would be great.
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post #2 of 6 (permalink) Old May 27th, 2013, 5:58 pm
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Have you unplugged the connector to the fuel pump under the right side plastic? It is no good just unplugging the relay unless you go to fuel pump connector and also try disconnecting that.

If the fuse stays good then your fuel pump is faulty. You may get lucky and find the wires to the pump itself (inside the tank are bad).

I hope you are replacing their 15 amp fuse on F4 with 10 Amp. I discovered recently that later bikes have 10 Amp fitted in that position and if the fuel pump seizes or the fuel filter blocks then 10 amp will blow, but 15 Amp seems to burn out the pumps. As I see it, when the fuel pump gets seized or blocked, pressure and current rises, but it can burn out before a 15 Amp fuse can blow. In the process of the pump motor burning out THEN the fuse blows and it is all too late to save the pump..

That was the easy bit and the good news.

If you disconnected the fuel pump and the fuse still blows, then you could have a problem with your Motronic ECU since that fuse feeds both the ECU and the pump. So your next step is to pull off the big fat connector on the ECU, turn on the ignition and see if F4 blows. If it does with both fuel pump and ECU disconnected, then the good news is you are probably looking for a wiring short somewhere and not a new ECU or fuel pump.



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Last edited by voxmagna; May 27th, 2013 at 6:05 pm.
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post #3 of 6 (permalink) Old May 27th, 2013, 7:14 pm Thread Starter
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Still blows with pump disconnected with relay in. I pulled the ecu and did not blow, but does that meaan the ecu is bad or did that disconnect all the wiring? Is there a way to test the ecu ?
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post #4 of 6 (permalink) Old May 27th, 2013, 8:52 pm
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Follow the pump wires to the electrical box, looking for worn insulation.
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post #5 of 6 (permalink) Old May 28th, 2013, 5:17 am
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I pulled the ecu and did not blow, but does that meaan the ecu is bad
Well I did help you with what I thought was going to be the 'either/or'.

A 15 Amp fuse is a relatively big fuse, so blowing it means a serious fault, and even more serious if you unplugged the fuel pump and it still blows.

I am a bit puzzled by the problem linking to the fuel pump relay. The ECU does control the fuel pump relay coil with a relatively small current and I suppose you could have a wiring short or cross point short in the wiring from the ECU to the fuel pump relay. I think a short inside the ECU so bad that it blows a 15A fuse would mean it is toast. But a short in the wiring loom between the ECU plug and the relay box may be a life saver (for your ECU).

OK so there is something else to try first before moving on to check wiring between the ECU plug and everything else: Lets say you have a short in the fuel pump power wiring AFTER the relay. The relay is turned on by the ECU to power the fuel pump. Removing the relay would stop fuses blowing. Also, removing the ECU plug would stop the relay being turned on, so a short after the relay on the power side would not blow the fuse. Before you think the expensive ECU is dead (and that is a possibility), check out the wiring coming off the fuel pump relay for short circuits. I assume you have disconnected the fuel pump at the tank connector and you did actually disconnect the correct connector and not the fuel tank sender? In fact, with the ignition turned off,you should be able to poke your resistance meter across the terminals going back into the loom (relay) and in the opposite direction towards the fuel pump. The fuel pump should have a low resistance around 5 ohms. There should be no resistance measuring back from the pump connector to the relay box.

Also check the circuit diagram to see if the handlebar 'kill switch' has any wiring linked to the fuel pump relay. Some bikes have aftermarket theft alams fitted. I know my alarm has its wiring spliced into the fuel pump relay circuit and these alarm installers do not always do a decent wiring job and the alarm units can go faulty.

You need to stop blowing and replacing fuses or risk further expensive damage. Buy yourself a Clymer manual if you do not have one to study the wiring inter connections between the ECU connector and the relay box including the fuel pump.



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post #6 of 6 (permalink) Old May 28th, 2013, 11:43 am
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Check the pump wires where they come out of the hard sheating under the tank. Mine were compromised right there and would have eventually contacted together and blown the fuse or even just getting wet could have brought out the gremlins.

That was hard to see, almost missed that when re-installing the tank. I think they broke just from flopping around and the weight of the connector, they should be ziptied to the pump flange as per the pictures in the manual.I went a few steps further.

And I was re-installing the tank because I had to replace the fuel filter at way less than the recommended milleage. Plugged almost solid and the only signs were stalling when starting in cold weather. Never blew the fuse. Yes I did the 10A mod for now but when I have more time will install a 5A just for the pump.

I don't know how long I ran with the plugged filter, did not like that bad for the pump. Tests OK for fuel pressure and glad that some have found easily available/cheaper alternatives at autoparts. Just in case it dies on the road.....I think I can get going again.

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