Fuel Pump Woes on a 1999 R1100RT

[MontanaMark]

Hi All,

 

While riding in Wyoming, my fuel pump just quit.  It ran long enough to suck the rest of the fuel out of the lines, then died.  Once pulled over, I turned off the key.  Turning on the key again did not start the fuel pump pre-pressurize.  No bzzzz.  Bummer.  So after a tow to Pinedale and a 18 hour recovery trip, I have it in my shop.  

 

I've pulled the pump mount plate, then detached the pump from the plate.  Sure that the pump had died, I jumped the pos & neg terminals to the battery only to be very surprised that a bunch of gas shot out of the pump.  So, pump works.  Checked the 15A fuse in position 6 of the fuse box with a VOM meter and got 100% continuity.  Just to be safe, I put a known good 15A fuse in slot 6 of the fuse box.  I haven't remounted the tank because I believe that something may be amiss with either the tank connector or the wiring.

 

When I check continuity between the brown connector and the brown wire inside the plate, I get no resistance.  Same with the green wire.  Here's the rub, check between the brown connector and the green connector, either from the tank connector or on the plate also show no resistance.  I would think that the green would be pos and the brown neg and shouldn't have connectivity.  Am I missing something?

 

Does the HES also figure in here?   Could a failed HES cause the fuel pump to not pre-pressurize or operate?

 

So, what else can I check?  

[Jim Moore]

Similar thing happened to me. It was a bad ground.

 

 

[dirtrider]

11 hours ago, MontanaMark said:

Hi All,

 

While riding in Wyoming, my fuel pump just quit.  It ran long enough to suck the rest of the fuel out of the lines, then died.  Once pulled over, I turned off the key.  Turning on the key again did not start the fuel pump pre-pressurize.  No bzzzz.  Bummer.  So after a tow to Pinedale and a 18 hour recovery trip, I have it in my shop.  

 

I've pulled the pump mount plate, then detached the pump from the plate.  Sure that the pump had died, I jumped the pos & neg terminals to the battery only to be very surprised that a bunch of gas shot out of the pump.  So, pump works.  Checked the 15A fuse in position 6 of the fuse box with a VOM meter and got 100% continuity.  Just to be safe, I put a known good 15A fuse in slot 6 of the fuse box.  I haven't remounted the tank because I believe that something may be amiss with either the tank connector or the wiring.

 

When I check continuity between the brown connector and the brown wire inside the plate, I get no resistance.  Same with the green wire.  Here's the rub, check between the brown connector and the green connector, either from the tank connector or on the plate also show no resistance.  I would think that the green would be pos and the brown neg and shouldn't have connectivity.  Am I missing something?

 

Does the HES also figure in here?   Could a failed HES cause the fuel pump to not pre-pressurize or operate?

 

So, what else can I check?  

 

 

Morning MontanaMark

 

I guess we need to start with your resistance measurements (or your interpretation of resistance measurements).

 

I don't see how you could have NO resistance?  Are you  confusing resistance with continuity? What ohm scale were you using?

 

Even a 12"  length of good condition 4mm copper wire has some resistance, very low resistance but it does have resistance.  

 

The HES does  figure in to fuel pump operation BUT only during engine cranking or running, the first key-on 2 seconds of initial fuel pump run doesn't depend on the HES.  

 

The Motronic does operate the fuel pump so that needs to be powered up & working.

 

Re-check your pump pass though wiring to make sure that you don't have an open in the brown or the  green/white wire (might even want to do that off-bike under load with a battery & 12v light bulb (hook 12v light bulb to the inside where the pump hooks up then run 12v to the green/white & brown wire to see if the bulb lights at full brightness.

 

Don't run the fuel pump without any fuel for more than a nano second as the pump is fuel cooled & fuel lubricated so running it dry will quickly burn it up.

 

Was/is you dash RID working (reading properly) when the problem happened? That is a good indication of power to the pump circuit (not to the pump itself but to the pump circuit).

 

Re-check the pump pass through for continuity on the pump wires then report back & we will go from there. You need to see infinity (open)  between the brown & green wires   & some (be it very low) resistance on the brown & green  wires through the passthrough.  Don't put your fingers on the metal part of the  ohmmeter probes as your meter can read that.

 

You might be fighting a  problem in the pump pass through, or a bad fuel pump relay, or a Motronic problem, or an open wire, or ????

 

Was it raining during your ride when it quit?

 

 

 

 

[MontanaMark]

Thanks for your input, Dirtrider.  Yep, sorry about the nomenclature confusion.  I meant continuity in all cases.  I was really interested if there was a wire fault.

In any case, I removed the fuel pump relay, to get the part number and check a parts fiche for cost.  I reinstalled the relay and just for S & G's grabbed the whole mounting plate and plugged it in to the connector.  Turned on the key and the pump ran.  Shut it off immediately and reinstalled the plate in the tank.  I also sprayed some CRC electrical cleaner in both of the connector sides.   Put the tank back on and took her for a ride (just up and down the street). 

 

So I really don't know the root cause of the malfunction.  I suspect either the connector or the relay.  Everything seems to be fine, but I'm going to replace the relay in any event and keep an eye on the connector.

 

Anyway, thanks for the help.

 

Cheers,

Mark

[dave_a]

Mark, my FP relay started erratic behavior. Eventually left me stranded on an interstate. Cooled off, started up as normal. A challenge to troubleshoot.

DR had me wire parallel LEDs into the igntion & fuel circuits to monitor each. Finally caught the fuel circuit failure.

Comparing resistance in the relay windings (compared to the horn relay) showed big difference. Its a common auto relay. Left pt# info in the oilhead  parts cross reference list.

 

[MontanaMark]

Thanks dave_a,

 

Yeah, I went down to CarQuest to get a new relay but they couldn't cross-reference it.  I pick one up from MaxBmw or some such.  

 

I would be interested in how to wire the LED's into the circuits.  Since I'm not sure of the root cause, I'd like to be able to monitor the relay.

 

On a side note, the guy at CarQuest had one suggestion:  he said that his sister had a Chevy that displayed intermittent fuel pump failure.  The problem turned out to be commutator brushes/springs.  I had mentioned that the RT was 20 years old, which triggered his memory of his Sister's car.  Ultimately, the brushes wore down enough that the spring tension was not strong enough to keep the brushes in contact with the commutator.  Thus the failure.  So buying a backup fuel pump may be a wise idea.

 

Since my trust level in a 20 year old bike is now somewhat damaged, I need to ride a little to regain that trust.  It's also a good excuse to get a newer RT, for which I've begun a search.  Looking for a '14 or newer water-boxer.  For some reason, I can't justify paying over 30k for a new one.  You know what they say: the cheapest part on a BMW is the nut on the seat.

 

Cheers,

Mark

[dave_a]

Mark, the relay is a Carquest R3154.

It lacks the ridge on the top of the case.

I use a small piece of foam to hold it in place against the cover.

I carry a spare now.

[MontanaMark]

Dave_a,

 

Thanks for the info.  I'll look into it today.

 

Cheers,

Mark

[dirtrider]

17 minutes ago, MontanaMark said:

Dave_a,

 

Thanks for the info.  I'll look into it today.

 

Cheers,

Mark

 

 

Morning Mark

 

You really don't need to carry a spare relay, if the fuel pump relay ever gives you a problem simply swap it with the horn relay (relay right next to the pump relay). That handles the fuel pump relay replacement, then honk the horn  (if it honks that means the old fuel pump relay is currently working OK).

[MontanaMark]

Dirtrider,

 

New info is always good to know.  I'll file that one away as "Hmmm, I didn't know that before".

 

Cheers,

Mark

[wbw6cos]

Why would not the relay work for the fuel pump but will work for the horn?  Is it the amount of current that runs through them?

[dirtrider]

29 minutes ago, wbw6cos said:

Why would not the relay work for the fuel pump but will work for the horn?  Is it the amount of current that runs through them?

 

Afternoon wbw6cos

 

I don't understand your question, what are you looking for here?

[wbw6cos]

Please disregard.  Sorry for the confusion.