Bucking Bronco

[Scooterbob]

Problem. Got carbs all done finally and now the damn fuel pump isn't getting voltage! Manual says "check voltage at back of fuel pump relay on Red/white. That's good. Reconnected harness to relay and still nothing on Black/blue wire going from relay to the pump. Grounds good and checked every plug possible. Even tried battery straight to pump and pump is good.

Ideas? I cannot even see if my carb cleaning helped anything......

[Scooterbob]

Ok, day number two (and final day because I must drive this to work tomorrow).  Still no fuel pump cycle.  Checked as many connections as possible.  Also threw the battery on the charger overnight, so I can start fresh again.
The only thing I have done between when the pump cycled fine and now is clean the carbs and change some gauge lights.  Didn't even get to putting the relay on the coil circuit yet. Any ideas as to where to check again?

SOMEONE PLEASE HELP!!! 

[andyb]

Killswitch, sidestand switch, etc.

Unplugged harness connections, or corroded/crappy connections.  No power at the pump itself?  Go from the pump and work backwards... Wonder if you forgot something when you had the dash to bits?  

Turn the key on, what lights up, and where do you have and not have power?  Got a wiring diagram to work from?

[Scooterbob]

Killswitch, sidestand switch both check good from what I can tell.

Turning on the the key lights up my green neutral light and all dash lights, headlight, taillights come on normally.  Starter turns over smooth. 

No power at the pump itself, correct.  Have good voltage going in to the fuel pump relay, but nothing coming out on the blue wire that goes directly to the pump (when key is turned on).  Possible that I could have bumped something when doing the dash lights, but I only took off the speedo cable and two main connectors to the gauges when I worked in that area.  Those are all reconnected good, but I will check again.

Yes, I have a diagram to work from, and the manual tells how to very basically check this problem.  Says I should have 12 volts at red/white wire on harness of pump relay (and I do).  Then it says to plug harness back in to relay and probe blue wire from back of it to check for voltage when key first turned on (I have nothing, like I mentioned above).  Checked all connections in the area, but still nothing.......

[Yamifj1200]

Bob, If you have voltage going to the fuel pump relay and no voltage at the pump the fuel pump relay might be bad. Since you say the pump works fine when connected to a 12 volt power source the relay is the only item sending voltage to the pump from the wiring harness.

Eric M

[Scooterbob]

Just found something interesting.  When checking connections at the pump relay, I found that the ground wire shorts to the positive......I think.  Let me explain. 
When I put my meter on the "beep" ohms setting, it shows that I have connectivity from the black wire on the back of the relay harness (unplugged) to the negetive terminal on the battery.  Ok, good.  But as soon as I turn on the ignition switch, it drops out.  Next, I took off the negative terminal on the battery. I then connected meter between black wire on back of relay harness (ground) and the other lead to the bare negative battery terminal (disconnecteD) and I still show connectivity.  Odd.
Soooo, my thoughts are to (for now) take the black wire from the relay harness and then run a new wire from the negative ground spot to the connector where I removed the black wire.  Basically reground the relay, but not using the original wire.  Hopefully that will shed some more light, BUT NOT SPARKS!!!!   

Does any of that make sense?

[Scooterbob]

IT'S ALIVE!!!!   

Traced back to the reserve switch.  Found that was what was shorting everything out.  Flipped and wiggled that switch a couple of times, and fuel pump fired right up.  Switch has always been kinda fragile looking and half hanging on.  Could use a new/good condition one, but for now I will see how I can bypass or stabilize this switch, since I've never had to use it anyhow.

Thanks all for the help and input.  If nothing more, confidence that it can be done is all I really needed I suppose. I humbly grovel at the forums' feet.

[Pat Conlon]

Way to go Bob.  I wonder if the dad gum fuel reserve switch was the cause of your bucking? 
This fuel reserve switch is a good item to add to the list of culprits to check, after the usual sidestand switch, etc, etc.

[andyb]

Congratulations on fixing it.

Now you can go to work.  So even when you win, you kinda lose...

[JCainFJ]

 Good Work!

IT'S ALIVE!!!!   

Traced back to the reserve switch.  Found that was what was shorting everything out. 

[Scooterbob]

Way to go Bob.  I wonder if the dad gum fuel reserve switch was the cause of your bucking?  

Although my throttle response is waaaaay better now, I am almost positive that the bucking was coming from this switch cutting my fuel pump off and on (while vibrating) when going down the road.  Now I know.  Definitely a good thing to check in the future.  Would have been nice if I hadn't had to strip the entire bike naked to figure it out though.

Congratulations on fixing it.

Now you can go to work.  So even when you win, you kinda lose...

Got no problems with going to work.  Keeps the moto wheels turning.  

[Marsh White]

This fuel reserve switch is a good item to add to the list of culprits to check, after the usual sidestand switch, etc, etc.

Yeah, and it is a good thing to immediately disable upon getting your FJ.  I know a lot of us have done that.  I don't need my motorcycle cutting off my fuel mid-corner to remind me that I'm getting low on gas - but that's just me!

It also makes a nice switch for something else - mine controls a cigarette lighter socket which turns my GPS on and off and also powers on a voltmeter for the battery.

[Scooterbob]

How did you bypass? Just unplugged it?

[Pat Conlon]

Dunno Bob.

Just do a continuity test on the reserve switch when the switch is set in the reserve mode. See if the switch is open or closed.  That'll tell ya if you just need to:
1) disconnect the switch or 2) disconnect the switch and tie the wire leads together. You want the fuel pump in the reserve mode 100% of the time.

Marsh, we know that there are times that, lifting off the throttle is not a good thing to do.....I never thought of the stumble/loss of power when the tank goes on reserve...yea, mid corner in a 80mph sweeper on Hwy 36.  That would suck. I'm gonna bypass the reserve switch on my '92 asap.  Thanks amigo!

[Scooterbob]

Photos for all who agreed that carbs may have been dirty.  Relay mod going on tonight.


Before teardown.


Side view of exterior dirt.


Dirty bowl!


Just a little dirt.....


Don't forget these little guys.