i need an electric diagram for the electric system on a 420D. we are blowing a fuse on the fuel system. anyone able to help?
There are 6 different 420D. What is your SN? I'll email you the correct schematic. I just took a look at a BLN and the fuel fuse powers the coils on all the relays in the fuse box, the lift pump relay and the shut off solenoid. Pull the relays, (Bosch style) and check terminal 85-86 and see if any have a direct short. This would be the essayist fix. Does the fuse blow immediately? If not, when? after starting? During cranking?
takes a while to blow the fuse. from one minute to fifteen. fuse blows after starting i believe. private message on serial number and email.
I just sent the schematics. They are the tricky ones to find. Good luck.
we took out all the relays and we still blow the fuse. is the the 18440 up diagram. our mechanic is tracing the "327" circuit. does this one go to the glow plugs as well?
If you use the "find" block and put the wire number in you can trace the wire fairly quick and see where it goes. because it doesn't blow the fuse as soon as the fuse is put in it may be a harness that is rubbed through. These type of problems are time consuming.
i think you are right. we also pulled a mouse nest out of one of the areas which is probably not a good sign.
We have a 420D in the shop now. Mice ate the harness and made a home on top of the trans.
mechanic thinks he found it. he found a relay that he thinks is bad on the fuel pump itself. he says it will run without it but blows fuse as soon as he puts it in.
That should be an inexpensive fix if thats it. Fingers crossed.
it wasn't the relay. without the relay it starts and runs. put the relay in while running it stays running. keep the relay in and turn off the key and start. the fuse blows again. same thing happens with the diode that is nearby the relay. take out the diode leave relay in and it starts and runs. put diode in it blows the fuse after about five seconds. sorry i don't have the relay number or fuse number right now. i will get it when i can.
Sounds like wire 977 is the problem or the elec priming pump on the fuel water separator. Check 977 to ground, if it is grounded then unplug the pump and check again. It could also be the pump relay, You can swap the two that are there together, they are the same.
What is the difference between vol 1 and 2?
I don't understand the the 977 circuit? It seems like 304 could power the lift pump without the relay and diod. Is it there for isolation and service troubleshooting?
Ok I understand why relay and diode are there now. I think we have a bad primer pump again. Either bad out of box or old relay would sometimes keep pump running for extended times and it got burnt up. We jumper primer pump and blow ten amp p9 fuse after thirty seconds.
Wow, this is an interesting problem. Somebody send me some diagrams, I'd like to see where we chase this little gremlin.
we took the old primer pump apart and found that it has a fine mesh screen on the suction side of the pump. although the pump shaft turned very roughly i felt that there wasn't anyway we could have gotten enough contamination into it to seize it.
977 latches the relay for the pump. When you turn the key to start, the starter cranks, and the fuel pump relay closes because it is fed from 304. then when you let go of the key it moves to run and because the relay was just closed it is now "latched" and it fed from 327. the diode prevent this from back feeding into the start circuit. The relay supplies power to 977 and the pump via 327 until the key is shut off. the relay then opens and will need to be turned to start to close it again. This is why when you change the fuel filter, bump the key to start it but just enough so it doesn't star then leave the key in run for a few minutes. Now the filters will prime. There are 2 volumes because the schematic it too big to be printed on one. When a harness moves to the other, it will give a location to find it on the other sheet. (example) LAMP ATCH HARN} CONN FP-C3 (SH 2 LOC B-1)
how do you know it is a latching relay? i had that though but i didn't think the diagram looked like a latcher.
You can check the pump, The current draw should be between 2 and 3.5 Amps. if the pump is bad it may be higher and then spiking and blowing the fuse. The relay is wired to initially close from 304 and then power itself to keep itself closed from 327 through the relay and then 977.
it is defiantly pulling to many amps. it pulls about 9 amps. do you agree that it isn't drawn as a latching relay?
i get it now!!! it is not true latching relay. it is a self propagating circuit. once 327 hits and the relay closes it energizes yellow which is the coil.
without the diode this circuit would keep the starter running all the time. i think we did have a bad lift pump out of the box.
Yes if the wires were connected. Without the diode the relay would not turn on. Possible. Can you swap it with one from another 420.
Not sure if other 420 8# in yard. Might be on a job. We pulled pump back out and hot wired it. It will not run. Also we cannot hear pump pumping anymore when it was in the hoe. Also when it was in the hoe we opened fuel lines and it did not pump fuel.
Sound like the problem.
That, and a pump pulling 9 amps is not normal.
i was gone from work yesterday, but i got a test message in the morning saying that the lift pump was replaced and the backhoe is in normal running condition. so unless something changed throughout its use yesterday it was a bad lift pump out of the box. thanks for all the help.
I also need a schematic for the 420d. We recently replaced the alternator and batteries and now the lights wont work and the switch to remove the loader bucket does not operate. The fuses all are good. Serial # is DCBLN01518
Lee-online could you send me over the different wiring schmatics you have for the at 420d .My email is [email protected] That would a most helpful.
Hi, I am also looking for the wiring diagram for my Father. He has written here he needs wiring for electric fuel pump relay wiring for 2004 420D cat backhoe can anyone help me out?
Need a machine Serial Number and an e-mail address to send the schematic.
Have you changed the diode yet? It might be shorted on the side that shouldn't have continuity. Diode half way up the engine block. Later Bob
Hello All, Hate to revive an old thread, but short on time... got a 420e that blows the fuel fuse, isolated primer pump and lift pump, it will idle, but throttling up past about 12k rpm blows the fuse again... pulling my hair out!