is there any kind of particular adjustment on a fuel shut off solenoid on a 773 bobcat, ive got to replace mine and it looks like it has some adjustment on the rod that goes on the pump, thanks for input.
If you're referring to like a G series 773 with the external mounted fuel solenoid, then yes, when you replace it there is one thing you need to verify. That shutdown lever on the injection pump will move until it hits an internal stop. When you connect the linkage for the fuel solenoid you need to make certain that the spool of the solenoid fully retracts all the way into the solenoid until it bottoms out before that fuel lever reaches that internal stop. If it's the other way around, fuel lever hits internal stop and solenoid spool isn't fully bottomed out inside the solenoid it will cause the solenoid coil to fail. Adjust the linkage so the solenoid spool fully bottoms out inside the solenoid.
Thanks for the help, i was thinking that after seeing the adjustment on the rod and of course buddy mine killed one those solenoids prematurely
Ok, Willie, I just stumbled onto this one. If I understand it, the solenoid opens the fuel passage when the coil is energized. When not energized, both the spool and the mechanism return to (towards) the fuel-closed condition. Isn't the solenoid simply either energized or not energized? When energized, does it not draw the same current regardless of the actual position of the solenoid actuator spool? Lol. I've never known you to be wrong, so I'm betting there is some obscure explanation for it. Let's have it!
Ive been using it about 3 weeks and it hasnt went bad yet, always something else taking my time, son broke a hydraulic cylinder on the dozer this eve so there a weld job and all the while im trying get freshly rebuilt excavator engine re installed, always plenty to do when you use old stuff
Well, it's a little more complex than simply on/off. The 773G used an external linkage 3 wire solenoid, pretty common arrangement as external linkage solenoids go. The solenoid consists of 2 internal coils, pull coil (high magnetic energy, requires high amperage to operate), and hold coil, (lower magnetic energy, requires less amps to operate). Since the hold coil is low magnetic energy it doesn't have the power to "engage" the solenoid spool, that's where the pull coil comes into play. The pull coil is momentary, controlled by the main controller, it's only powered up for a few seconds to simply "engage" the solenoid spool. Once engaged the main controller drops power to the pull coil. From that point it's up to the hold coil to keep the spool engaged. This is where it gets into physics that I can't explain, I only know from experience that if the spool isn't fully engaged (bottomed out) inside the solenoid, let's say because of incorrect linkage adjustment that the spool is only half way engaged inside the solenoid, then amperage will increase feeding the hold coil and it will cause it to prematurely go up in smoke. The spool must be fully engaged inside the solenoid or hold coil will go poof. It's physics. Like I said, I can't explain that, can only say it's real.
I think you did a great job explaining it. I wonder: When the spool reaches it’s full travel, does that cause the pull coil to de-energize? If so, if full travel is not achieved, the pull coil would never de energize. . . leading to continuous high current ( pull coil). The pull and hold coils are likely wound together. Makes sense that continuous high current would fry ‘em. Thanks for xplainin’.
The momentary action of the pull coil on a Bobcat is controlled by the main controller via the relay in the fuse box. The main controller trips the relay for just a few seconds on power up of the ignition, then it drops the trigger signal on the relay after a few seconds which drops battery power to the pull coil. Any three wire fuel solenoid requires some form of time delay to engage and drop power from the white wire (pull coil) of the fuel solenoid. An exception to that, there are some 2 wire solenoids out there that have an internal switch, battery voltage on the positive signal wire powers both pull and hold coils of the solenoid, but when the spool hits bottom it depresses a switch that drops power to the pull coil of the solenoid.
Ok. I’m getting it. The Bobcat and similar setups use time for de-energizing the pull coil. Interesting.