Turbo Fuel Pump Gremlins

Hi I've spent many hours reading the forums and buying parts but finally need some help that hasn't been addressed before. Since you're such a knowledgeable group I believe you can help. My fuel pump comes on as soon as I turn on my ignition switch. As it states on page 67 of the Turbo Service Manual it should not come on until the starter button is pressed. Mostly a safety issue. After studying the fuel pump circuit on the same page I've concluded I have a short to ground somewhere that I can't find. Also my pump quit on me twice last ride which could be caused by a short. Fuel pump relay tested good but I put in a different one just in case. So thats where I am now, afraid to leave town without a spare pump and wires. Open to suggestions. Thanks

 

What year and model? (You can add it to your signature if you don't want to try and remember to put it down every time you ask a question.)

 

DId you replace the fuel pump relay with the CORRECT relay, it should have a red paint mark on the bottom (where the connector plugs in):

The original style metal "cube" type relay has 5A8 inked on the top face and has a red-painted locking tab for identification; the later-style replacement is marked 25G on the top face.

Also, there are two different relays up there behind the fairing, the wire bundle for the fuel pump relay should have a piece of red electrical tape around it.

 

i don't want to pick on you Mr turbo but a "short" is when + goes to ground without any device in the path, thus the term "short". those lead to blown fuses and melted wires.
A "open" is when there isn't a complete circuit, like a switch that shouldn't be there. sounds like you have a intermittent open.
after all that, i don't know jack about FI except my bmw fuel pump starts when the key is turned on and my Suzuki's comes on when the start button is pressed.
most of these yamaha relays come apart and can be cleaned.

 

There is also a "tilt" switch/sensor that cuts off the fuel pump if too large a tilt from vertical is detected, that sensor might be a problem or a loose wire to it, etc.

 

Still don't see model number, but if it's a XJ650LJ this applies:

That looks correct per the wiring diagram. The start switch applies ground to one end of the fuel pump relay through a steering diode to energize the coil closing the fuel pump relay contacts and apply power to the fuel pump. So, if you have the fuel pump turning on with the key, then you do likely have a "short" on the low side of the fuel pump relay coil. Once the bike starts, the AC Generator and a couple of steering diodes keep the fuel pump relay energized.

Key off:
Remove the fuel pump relay and connect the DMM set to diode scale with the red lead connected to the W/L (white / blue) wire on the fuel pump relay socket and the black lead connected to ground, should have a high resistance.

Press the start button, should get a reading of approximately 500 ohms using a DMM.

Not sure how you verified the fuel pump stopped, but there are several reasons it could.

The pump could be failing intermittently

The switch that Chacal suggested (emergency stop) would remove all ignition power, so if the switch or the relay that it controls were intermittent you would have a sudden stopping of the bike, as power would also be removed from the coils and TCI.

Once the bike is running, there are two diodes that connect the low side of the fuel pump relay to the AC Generator to keep the fuel pump relay coil energized. So, the AC generator must be functioning correctly as well as the diodes and wiring that route to that point.

You can test the two diodes with the DMM also set to diode scale. Same point as before for the positive lead. Before disconnecting anything with the AC Generator place the negative lead of the DMM set to diode scale in the back of the Rect/Reg connector on each of the three white wires. Edit: Each of the three should give you a diode reading of about 500 ohms with the stator in circuit, the stator can be disconnected and two of the three should give you a reading of about 500 ohms.

One other question is the computer monitor, is it working normally? On most of the XJ's the fault detect is initiated after the bike starts directed by the output of the voltage of the AC Generator. It looks like on the Turbo model they used the fuel pump relay output for this purpose. Therefore, if the fuel pump relay energizes with switch on, then the fault detect sequence would also occur at that time.

 

Thanks, for the replies. All parts are correct and in their proper locations. Tipover switch is secure. Relay white wire blue stripe at the plug reads 472 on diode setting with the key on or off. The diodes are good, replaced with new just in case. I have a clear fuel filter. It's got fuel rushing through or fuel that's not moving. I believe last time the fuel wasn't moving I could still hear the pump running. So I'll try a new pump, still doesn't explain relay tripping with key on. Display works well. XJ650LJ

 

Key off:
You should get the 472 only when the starter switch is depressed. If you get 472 all the time, then something in the stator or wiring is going to ground, which it should not.

 

Exactly, I'm looking for suggestions because I can't find it. Stator plug was removed and wires soldered and sealed.

 

So I understand that as you get the 472 all the time. If so, my first suggestion would have been to disconnect the AC generator stator to see if the resistance goes to open. If so, then check the AC generator stator to ground. It should be totally isolated from ground.

Since the stator wires have been soldered, you could just disconnect the diode block and re-check. If you get an open, re-connect and try disconnecting the Rect/Reg plug. If the 472 remains with the Rect/Reg disconnected, then you can ohm the 3 white wires on the Rect/Reg to chassis at the Rect/Reg connector - probably best to disconnect the diode block again. If you get continuity to ground on the 3 white wires, then there is an issue with the stator or associated wiring shorting to ground.

Does it start the test sequence with key on, or when you push the start button, or when the bike starts? Curious for future reference.

Have you evaluated the charging system to see if it outputs full voltage? 14.5 +/- .3V at 2K RPM and above.

 

I didn't get to check with diodes unplugged, have to pull fairing and will wait until I get new pump. But I disconnected stator at R/R plug and still had 472. I checked stator to ground and all 3 wires had continuity to ground with diode block plugged in. I replaced the diode block already because I know we're close to finding my short to ground. Charging system is dead on @ 2k. Test sequence starts with key on. Thanks

 

The continuity to ground will need to be isolated and I am assuming it is a very low resistance? If any of the three wires go to ground, the other two will appear to go to ground also because of the arrangement of the stator in a "Y" configuration and the low resistance of the stator windings. You could wait until you get the fuel pump and check the wiring thoroughly again for damage causing the short to ground. However, since your stator connector was removed and soldered I suspect you will eventually have to unsolder the connections to isolate the stator and then check it independently to ground.

I don't own a turbo, but I believe once you get this sorted the status check will initiate with the press of the start button??

 

Thanks ,by looking at the fuel pump circuit the stator area is where the short must be. I'll have to take apart harness to trace every wire. On a side note, on the fuel pump relay plug on the white / blue wire there's a empty bullet connector coming out the back??

 

Just put a new pump in works great, but still comes on with key. I checked white/blue again with diodes unplugged on diode setting 50 key off, continuity to ground with key on.