Excessive ampage draw at fuse #6 (fuel pump) [SOLVED]

[sebas2357]

Greetings Gents,

I'm currently battling an issue where fuse #6 is pulling an excessive amount of amps. The correct fuse should be a 7.5A, but that was blowing consistently during very hot days. I decided to put a 10A fuse (I know HIGHLY unadvisable) and that seemed to hold up quite well, until recently. Last weekend that 10A fuse blew, so I figured it was time to get to the bottom of the issue.

So far this is what I've discovered/know at the moment:
1. The fuse is drawing 6 amps while idling. AFAIK normal ampage draw should be around 2.0A - 2.5A. Increasing/blipping the throttle does not increase the amp draw while stationary. I'm assuming the ampage draw is either increasing while in motion or when it gets quite hot given the I couldn't get the fuse to blow while testing.

2. Unplugging the fuel pump and cranking the moto displays 0 amp draw. Therefore, I believe this would rule out any phantom draw or wiring shorting of any kind. I removed the fuel pump from the tank and cranked the moto, with the fuel pump tank cable plugged in, and resulted in 0 amp draw as well.

I removed the fuel pump believing that the fuel pump screen might be dirty or clogged and found it to be good as far as I can tell. (Images attached). The pump appears to be an OEM bosch (also according to PO), but has no branding, so I'm unsure what brand it actually is. I've also replaced the fuel filter thinking it was dirty/clogged, and this resulted in no amp draw difference, still 6.0 amps. The only thing I can think off is that the fuel pump is faulty. From the images below, the pump seems to be fine, but I'm unsure how to test further. The tank was also very clean. I spoke with the PO, and he told me that he replaced the fuel pump last year, along with all the interior mounts, wiring, filter, and hoses.

Before I go and purchase a new fuel pump to determine if the pump is the issue, is there any way to test the pump? I'm stumped on whether it could be something else, any input would be very much appreciated.

Best,

Seb

[Laitch]

Outward appearance of a fuel pump is no indication of its internal condition. Diagnosis-by-parts-replacement can be a costly and unsatisfying experience. Using a higher amperage fuse in the place of the specified fuse could start an electrical fire resulting in the replacement of your wiring harness, or worse.

Are the replacement fuel lines in the tank SAE30R10? Did you check them for clogging? Have you determined the output of the pump at the fuel rail? Has the moto been running ok?

[caveman]

You could jump the fuel pump to the battery direct with amp meter. If the amp draw is the same than pump is going bad, if it is less than you have a bad wire or connection in the harness. Use the same jump method to isolate ground or hot side.

[Scott_]

Are the replacement fuel lines in the tank SAE30R10? Did you check them for clogging? Have you determined the output of the pump at the fuel rail? Has the moto been running ok?

I'm thinking with Laitch on this one, check your pressure at the fuel rail with everything connected. Could possibly be that the FPR is failing and causing excess pressure/load on the pump, or the return line could be restricting return flow.....

[The Mighty Gryphon]

Could be a clogged or stuck check valve where the return line goes back into the tank. 

[daveson]

Does the temperature warning light work? Is the fan working well? Has it been happening in motion, or say waiting at traffic lights?

[sebas2357]

Are the replacement fuel lines in the tank SAE30R10? Did you check them for clogging? Have you determined the output of the pump at the fuel rail? Has the moto been running ok?

Yep! I checked the fuel lines, they are BMW branded submersible fuel hose. I also checked for blockage at the hoses, and there was no obstructions/gunk etc. The moto runs perfect, it just simply blows 7.5A fuses within 10 minutes of start up, and has blown a single 10A fuse last weekend. If I run a 15A fuse, (which I did for further testing. please no scolding  ), it doesn't blow at all. I ran the moto with a fuse tester again and discovered that at cold idle, the draw is 6.0A. When fully warmed up, the draw is consistently 6.5A - 6.7A. Further, blipping the throttle when warmed up, the ampage jumps to a max of 7.3A.

I'm thinking with Laitch on this one, check your pressure at the fuel rail with everything connected. Could possibly be that the FPR is failing and causing excess pressure/load on the pump, or the return line could be restricting return flow.....

I currently don't have the tools to measure the pressure at the fuel rail, but will be borrowing some tomorrow and will report back on what the pressure is at. I believe that the pressure should be somewhere between 35psi - 40psi. Besides a reading between 35-40psi, is there any behavior I should be looking out for?

You could jump the fuel pump to the battery direct with amp meter. If the amp draw is the same than pump is going bad, if it is less than you have a bad wire or connection in the harness. Use the same jump method to isolate ground or hot side.

I'm a complete novice when it comes to hooking things up electrically and whatnot. Could you elaborate how isolating ground or hot side would work, as in the method of doing so? I understood jumping the fuel pump from the battery, that seems pretty straight forward, it's just that one part that I don't comprehend.

Could be a clogged or stuck check valve where the return line goes back into the tank. 

I visually checked the return line valve and couldn't observe any obstructions. I blew air into the valve as well, and could feel the air flowing just fine through the valve. Any advice on further ways to test the valve?

Does the temperature warning light work? Is the fan working well? Has it been happening in motion, or say waiting at traffic lights?

I've never had the temp light turn on, but can confirm the fan works fine; it kicks on when it's supposed to. The 7.5A fuse will blow within 5-10 minutes of riding. If I replace the it with another 7.5A fuse, it will blow again. This will occur regardless only when throttle is applied, i.e from a stop, or increasing throttle on the freeway. It won't occur while idling.

The first time that I experienced a fuse blow was when I was traveling back home after purchasing the bike. I rode over 8 hours from St.Louis to Atlanta without a problem. As soon as I crossed over into Florida during midday, the fuel pump fuse blew when I accelerated hard to over take another vehicle, I was doing around 75-80 mph. I observed that the fuse that blew was a 10A, but the fuse cover said 7.5A. I plugged a 7.5A fuse and was back on my way. Given that the fuse had just blown, I decided to reduce my speed to 65MPH, 5 minutes later, the fuse blew while on the travel lane (no hard acceleration). I realized that the PO probably had a similar issue with the 7.5A fuses. I plugged a 10A and managed to make it home to South Florida without another incident. That was until last weekend when I was on my way home from being out, and the fuse blew while at a red light. As soon as I began accelerating from the light, the bike shut off and coasted to a stop. I observed the 10A fuse blew, swapped another 10A fuse in, and have parked the bike since.

The only similarity between the first time the 10A fuse blew, and last weekend, was that they both occurred during really hot days, in excess of 90F degrees.

[rbm]

I'm a complete novice when it comes to hooking things up electrically and whatnot. Could you elaborate how isolating ground or hot side would work, as in the method of doing so? I understood jumping the fuel pump from the battery, that seems pretty straight forward, it's just that one part that I don't comprehend.

What Caveman is getting at is a diagnostic method to identify IF wiring is bad and IF IT IS BAD, a way to identify the particular wire that is bad.

So first you're going to completely isolate the pump from the harness by taking off its wires in the tank (or unplugging the tank connector from the harness), attach wires to the pump terminals one of which is putting your ammeter in series with the circuit and then attach it to a battery.  If the current drawn is lower than 6.5A, then the conclusion is bad wiring.  If the current drawn is 6.5A, then it has to be the pump which is bad.

If the wiring is bad, which one of the wires is bad??  Isolating the power side involves disconnecting the +ve side of the pump from the circuit and wiring up your ammeter between the pump +ve and the bike battery using a completely separate piece of wire.  That way the current flows from the battery, through the ammeter, through the pump motor, back to ground through the bike harness.  If the current draw goes back up, the problem is the ground wire.

Repeat the above for the -ve of the pump.  If the current goes up to 6.5A, the problem is with the power to the tank.

This is the process of isolating circuits to debug them.

[sebas2357]

I tested the fuel pressure today and can confirm there are no issues regarding pressure. The gauge read a consistent 35-37 psi at both the entry hose and return hose. Ruling out the FPR, it seems that the problem lies within either the pump or the wiring. It's been raining lately so I haven't gotten a chance to test the fuel pump by jumping it with the battery. The weather should be clearing up a bit tomorrow afternoon. I'll provide another update with my findings then.

[caveman]

Thanks Rob!

I'm still pondering why it blows (or current draw increases) with increase of throttle. Alternator kicking in and regulator running at higher than normal?

[Scott_]

Looking at the circuit diagram, there are 2 items connected to fuse #6.
1) fuel pump
2) control/sensor power for the temperature relay(fan/light).

As you say this is happening when hot, and under load(which is how it gets hot), there could be an outside chance that the temperature sensor could be failing.
Another potential issue could be the fuel pump relay being affected by the engine heat and vibration.
The pump draws a specific amount of watts(power), if the relay contacts are going bad/weak it could cause the pump to draw more current(due to reduced voltage).

[daveson]

I'm still pondering why it blows ... with increase of throttle.

Me too.

Just throwing another wild card into the mix.

The single time the fuse blew while not accelerating, was it uphill? Does the low fuel light work? Or the fuse blows on an incline if fuel level low and on the side stand? Dunno if the white wire is positive or negative, sposing positive.

Is one of the wires tangled with the rod to the fuel level float, or something?

[sebas2357]

The single time the fuse blew while not accelerating, was it uphill? Does the low fuel light work? Or the fuse blows on an incline if fuel level low and on the side stand? Dunno if the white wire is positive or negative, sposing positive.

Is one of the wires tangled with the rod to the fuel level float, or something?

The first time the 10A blew on my way back home was on a flat freeway, under hard acceleration. Last weekend's 10A blew from a stoplight, no hill (this is florida  ). All the 7.5A fuses will blow at the slightest increase of throttle after 5-10 minutes of riding. The fuse doesn't blow with the bike just idling on the center stand or side stand, regardless of what fuse is in there 7.5A, 10A, 15A, etc. I have the 7L and 4L low fuel style lights. The 7L does not work at all, but the 4L does work. AFAIK, the wiring inside the tank is fine (but will be testing later today). I have an 85' K with the fuel-strip type sensor, so there is nothing tangling either wires going to the fuel pump.

[sebas2357]

I can confirm that neither the fuel pump, nor the positive or negative wires are the problem. I jumped the pump on the battery and got a 2.8A draw. Both negative and positive wires isolated drew around the same ampage, 2.8A. I reran the fuse tester on fuse #6, and discovered that the draw is now 7.0A at idle. When first cranking/starting up and blipping the throttle causes some erratic amp draw at the tester; at one point witnessing 10A+ draw. I have attached a video showing this. I'm completely stumped now at this point. I saw the suggestions that the temperature sensor could be faulty or failing, and the possibility of a bad fuel pump relay. How would I go about testing both to see if they are the root of the problem?

Here's the link of the video showcasing the erratic amp draw behavior:   

[Laitch]

The test for the coolant temperature sensor is in the troubleshooting guide the link to which is at the bottom of the first post in the Repair Guidance section. I doubt its malfunction would be creating this resistance but testing it is relative cost-free and could be a pleasant few moments in the kitchen, or wherever water is boiled in your neighborhood. There are a couple of useful videos on YouTube—one of which was posted here recently—about how to test relays.

[daveson]

A couple of quick checks. Removing the temperature sensor relay might reduce the Amp draw. Wiggling the green/white wire to the sensor might have an affect, or the green/white wire to the pump.

 I think I've read some people deliberately disable the brown/black wire (7 litre warning light) cause it's annoying. I'm wondering if the fuel level warning wires are clean and good. 

[Scott_]

The power for the fuel level warning lights comes from fuse #1, not 6.
The warning light sensor/switch does share the brown ground wire at the tank, but that is all.

For the radiator fan, Fan motor power comes from fuse #7, but the control power for the relay comes from #6.

[daveson]

Also, you probably don't need to consider the fuel injection relay, cause it's upstream of fuse 6.

[sebas2357]

I ran the bike without the temperature relay connected and got the same amp reading. About 7.3A now. Wiggling the wires amounted to no difference in amp draw. The only thing that causes an increase in ampage is increasing the throttle. I have a feeling that it could still be the fuel pump after observing some weird behavior while testing the temperature relay. There are times at idle when the pump seems to power down or reduce fuel draw (the normal hissing of the pump fades and disappears), then the bike will begin to stumble for a second, and then will continue idling just fine. When the pump seems to start this behavior of "powering down", the amp draw increases upwards of 13A-14A. If I increase throttle input, the pump powers back on to its usual hissing noise and amp draw drops to the usual 7A- 7.3A. I'm not sure if anyone can make sense of this, but is there a possibility that the pump may not be receiving adequate voltage? I'm a total novice of electrical knowledge, someone more knowledgeable may be able to provide their thoughts of what may be causing this behavior. 

Also, I observed while disconnecting the battery that the positive battery terminal has two terminals? I'm not sure if this is normal, or if the PO did some shoddy electrical work and the double terminal shouldn't be there. This could be completely unrelated, but I just want to rule this out as a possibility. I've attached the terminal in question below.

As always, thank you guys for your invaluable input.

Seb

[The Mighty Gryphon]

You say the pump output drops and the engine stumbles about the time the current spikes?  If that is true, I would suspect you have a pump problem.

Something is making it hard for the pump motor to run, increasing the current draw while reducing the fuel output.  First thing that comes to mind is that the pump has sucked in some foreign matter.  You might be able to clear it by running the pump in reverse, but I doubt it.  I think the plan going forward would be to do a good flush of the tank, and probably a pump replacement.

[rbm]

It's possible that the fuel level sensor and pump wires inside the tank are deteriorating.   What is the condition of the insulation on the wires leading to the fuel pump?  Is the insulation intact and flexible, or is it cracked and hardened?  One test is to see of there is no contact between the wires.  Disconnect the fuel tank from the harness and remove both wires from the pump.  Begin to test resistance between the Green/White wire and the Brown wires.  There should be infinite resistance between the Green/White wire and any of the Brown wires but if you get any sort of reading of resistance, it means that there is an internal short that is causing excessive current draw.

Another indicator is that you suspect the PO ran his own wiring.  Is it possible that the PO ran some aftermarket accessory off of the Fuse #6 circuit?

[sebas2357]

You say the pump output drops and the engine stumbles about the time the current spikes?  If that is true, I would suspect you have a pump problem.

Something is making it hard for the pump motor to run, increasing the current draw while reducing the fuel output.  First thing that comes to mind is that the pump has sucked in some foreign matter.  You might be able to clear it by running the pump in reverse, but I doubt it.  I think the plan going forward would be to do a good flush of the tank, and probably a pump replacement.

To completely rule out the pump, I've gone ahead and ordered a new fuel pump which should be arriving tomorrow. I'll update then on my findings.

It's possible that the fuel level sensor and pump wires inside the tank are deteriorating.   What is the condition of the insulation on the wires leading to the fuel pump?  Is the insulation intact and flexible, or is it cracked and hardened?  One test is to see of there is no contact between the wires.  Disconnect the fuel tank from the harness and remove both wires from the pump.  Begin to test resistance between the Green/White wire and the Brown wires.  There should be infinite resistance between the Green/White wire and any of the Brown wires but if you get any sort of reading of resistance, it means that there is an internal short that is causing excessive current draw.

Another indicator is that you suspect the PO ran his own wiring.  Is it possible that the PO ran some aftermarket accessory off of the Fuse #6 circuit?

From what I can tell, the insulation on the wires seems fine, no cracks breaks or anything that could compromise them. I will go ahead and test them for resistance once the weather clears up again later today. The rain has really delayed any troubleshooting that I've been wanting to do.

I only suspect modified wiring by the PO based on the positive battery terminal having two connectors. From the 4 bikes that I've owned, I've never seen a battery terminal wire having two connectors. Is this normal on the K bike? Or should it only be one connector? I've tried searching online regarding this, and from the replacements kits I've seen online, it seems that the battery terminal wires should only have one connectors, both positive and negative. If someone could confirm that with their positive battery cable that would be great. I might have to poke around to see why there are two positive battery connectors.

[Laitch]

I observed while disconnecting the battery that the positive battery terminal has two terminals? 

To completely rule out the pump, I've gone ahead and ordered a new fuel pump which should be arriving tomorrow.
If someone could confirm that with their positive battery cable that would be great. I might have to poke around to see why there are two positive battery connectors.

The diagram extract below is from Clymers; it's from a diagram of  early K100RS wiring. The battery in the diagram has three terminals on the positive connection. OMG! Two is not uncommon. Look at an electrical schematic like the extract I posted. There are some available on this site and around the Web.

Regarding your new fuel pump purchase, if you've performed the tests correctly as prescribed by rbm and caveman. and described their results correctly, congratulations! You've bought yourself a spare fuel pump.

In your travels beneath the tank checking grounds, if you think terminals that look like those in the photo below are in acceptable condition, you're mistaken. They need to be cleaned with an abrasive pad until they're bright. You can coat the connections with petroleum jelly or commercial protectant when you've finished cleaning them.

[rbm]

What's you're looking for is an unaccounted for load on that circuit; something that is out of the ordinary.

In post #13, you confirmed that the pump draws 2.8A under normal operation.  In that same post, you confirmed that taking out the temperature sensor from circuit did not change the current draw appreciably.  So that means (1) those two loads are operating within normal parameters and (2) there is some unknown load drawing approximately 4A of current from that circuit.  Have you tried the simple test of removing the pump and temperature module from the circuit and seeing what the residual current draw is on the circuit?  If you see 0A in your tester, the problem still lies with the tank and the pump.  If it shows about 4A, there is something else on your bike drawing that current.  It will either be an aftermarket accessory added by the PO or a wiring fault in the harness.  Can you make that test and describe the results?

[daveson]

I have an early model brick like yours, two positive battery connections is normal.

I've been thinking its hot in the US this time of year. It sounds like you don't have a shed and there's been a lot of rain in Florida. Has this problem only been when your bike is wet? Maybe the tank connector green/white is sharing dirt and damp with a neighbour.