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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 989
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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My bobcat escavator 335 keeps blowing the fuel seloniod

Customer Question

My bobcat escavator 335 keeps blowing the fuel seloniod fuse. I put a new selonid in it and still wont start
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  Fieldtech59 replied 1 year ago.
Is it blowing fuse #4 for the fuel solenoid? Still blowing it after you've installed a new fuel solenoid? Do you hear three short beeps from the alarm when this happens?
Customer: replied 1 year ago.
No and no
Customer: replied 1 year ago.
No
Expert:  Fieldtech59 replied 1 year ago.
Wait, what? If it's not blowing the fuse for the fuel solenoid (relay), then which fuse is it blowing?
Expert:  Fieldtech59 replied 1 year ago.
Crap, I'm sorry, my mistake, fuse #8 for FUEL, no?
Customer: replied 1 year ago.
Fuel selenium blows I don't no what number it is
Customer: replied 1 year ago.
As I said the fuse for fuel selenium is the fu see that blows as soon as you touch start button
Customer: replied 1 year ago.
Do you have any idea I'm stumped
Expert:  Fieldtech59 replied 1 year ago.
Stand by, I'm typing some info I hope will help you.
Expert:  Fieldtech59 replied 1 year ago.
Ok, of course I don't know exactly which series 335 you have, so I can't make comments that are specific, rather general Bobcat stuff. When you take that cover off of the fuse box, unless someone has removed it, there should be a decal on the inside of that cover that describes each fuse, the fuse number, and what the fuse powers, also ID's the relays in the fuse box. Now, the Bobcat fuel solenoid. It has two separate windings inside it. One winding, hold, is a magnetic winding to "hold" the solenoid engaged when it's powered up. However, the hold winding doesn't have enough magnetic strength to "pull" the solenoid in. That's where the second winding comes into play, the "pull" winding. The trick to the pull winding is it can only be powered up for a few seconds, any more than that it will smoke the solenoid. Depending on the model series, the solenoid will have either two wires (red for hold, white for pull, and grounds through the solenoid case), or it will have three wires (red for hold, white for pull, and black for ground). Now here's how it works. When you power up ignition you're sending an input to the main controller (ECU) to power up the fuel solenoid. The ECU then does two things; 1) it sends voltage directly to the red wire (hold) on the solenoid, and 2) it sends power to the fuel relay inside the fuse box. The relay trips, this sends battery power via fuse #8 to the white (pull) wire on the solenoid. After a few seconds, the ECU takes power away from the fuel relay, relay disconnects fuse 8 from the solenoid. If you're blowing fuse #8 FUEL, there's something wrong in that circuit, it's not a problem with the ECU, the problem is either with the relay (never really seen one short out inside and do this though, but I suppose it's possible), or a dead short to ground in the wire that runs from Fuel Relay to the white wire on the solenoid, or there is a fault with the solenoid. Yes, I understand you put a new one on, just saying don't discount that it can still be the problem. If you are blowing fuse 8, first, pull the Fuel relay out of its socket. Now power up the ignition and see if it blows the fuse, it shouldn't. If it doesn't, turn off ignition, put relay back in socket, disconnect the plug at the fuel solenoid. Now try it again, power up and see if fuse blows. If it does, you have a short in the wire going from relay to solenoid. Work your way through this and let me know what you find.
Expert:  Fieldtech59 replied 1 year ago.
I don't have the manual on the 335 here on my home computer, but I pulled a pic of the fuse box from a 334, I'm hoping it's pretty much the same as yours. >
Expert:  Fieldtech59 replied 1 year ago.
One thing that might happen depending on the programming of the ECU, on later models, if you disconnect the harness plug at the solenoid and power up the ignition, the ECU see's a problem and won't power up that circuit, makes it so you can't test voltage on the wire going from relay to the white wire on solenoid. In that case, you simply test the wire with an Ohm meter. Pull the Fuel relay from its socket, disconnect the harness plug at the solenoid. Now, stick the probe on your Ohm meter is terminal 87 of the relay, that's the terminal that goes to the white wire at solenoid. If it lights up your Ohm meter when you do this, with the harness disconnected at the fuel solenoid, you have a dead short to ground on that wire. See attachment for location of terminal 87 of relay socket. >
Expert:  Fieldtech59 replied 1 year ago.
BTW, I rejected your request for a phone call for two reasons, 1) I'm on Eastern Time, gotta hit the rack soon and wanted to get this info to you as quick as I could, and 2) as you can see with the attached pics, kinda hard to describe some of this stuff on the phone. Gotta go to Olin Chem tomorrow to work on a machine, prolly be there the whole day, I'll check back in tomorrow eve to see how we're doing.
Expert:  Fieldtech59 replied 1 year ago.
Any news from today?

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