Cat 248 Fuel Shutoff Short

Steve Frazier · Jul 20, 2016

I have a 2000 Cat 248 # 6LZ00433 that's popping the fuse to the fuel shutoff solenoid. The relay was bad previously and I've replaced it, along with the shutoff solenoid. You may recall I had a reman engine installed a couple years ago and the solenoid didn't match the wiring harness. My mechanic direct wired it temporarily and I've replaced the solenoid and replaced the plug on the harness to factory. Machine starts for a couple seconds and then pops the fuse. There's nothing obvious I can see and the harness disappears down into the darkness. Does anyone know of any trouble spots where the harness might chaff?

Mark250 · Jul 21, 2016

hi Steve, the brake light circuit if fitted also runs off that same fuse for the fuel solenoid. First off I would disconnect the solenoid and see if fuse blows. then isolate brake circuit by disconnecting connector#8 in sch below.
failing the above you can either chase the fault down or run another from fuse to solenoid.
the solenoids are usually a 3 wire set up with a pull in coil and a run coil. I am a bit concerned that it has been hard wired ,if you are using only the pull in side of the solenoid to operate with you risk damage to wiring and or solenoid

Mark

Steve Frazier · Jul 21, 2016

Thanks for the schematics. I don't have brake lights on my machine. The solenoid had been hard wired properly, the plug was just eliminated because it didn't match. Wires are color coded. I know red is run, I assume black is ground and white is start? I'm afraid I'm going to have to trace it out, but there isn't much room to access or see what's going on.

thepumpguysc · Jul 21, 2016

Did this JUST happen all of a sudden?? as in.. it had been running ok and then it started blowing fuses..
I ask because they are adjustable.. and if they aren't adjusted exactly right.. they either burn out or blow fuses..

Mark250 · Jul 21, 2016

thepumpguysc said:
Did this JUST happen all of a sudden?? as in.. it had been running ok and then it started blowing fuses..
I ask because they are adjustable.. and if they aren't adjusted exactly right.. they either burn out or blow fuses..

good point they need full travel and not hang up part way
Mark

Steve Frazier · Jul 22, 2016

Yes, it had been running fine and started blowing fuses. It doesn't blow the fuse instantaneously either, takes about 3 seconds to blow. When you say "they" are adjustable, does that mean the fuel solenoid?

thepumpguysc · Jul 23, 2016

If its a 3 wire set up.. connected to the shut off linkage on the inj. pump externally.. yes, in most cases the s/o sol. arm is adjustable..
A picture is worth a 1000 words..

Steve Frazier · Jul 23, 2016

Sorry, I didn't even think of pics.

The pin on the solenoid is fully extended and retracts when energized. It inserts into a close tolerance hole on the back of the injection pump, there's no external linkage. There's a third black wire hidden under the white and red, I didn't realize it wasn't showing. This is the one I removed.

Here is the new solenoid installed in the pump. Had to take this picture blind, I couldn't see the screen at the angle it's in. I repaired the machine harness to the factory connector.

thepumpguysc · Jul 23, 2016

OK, no adj. on that one.. BUT.. are you SURE it takes a paper gasket?? I've seen them w/ an oring but not a paper gskt..
If it takes an oring, the pump housing will be cut/grooved for an oring..
Just a thought, but maybe the paper is cutting down on the "ground" in the electrical circuit..

lantraxco · Jul 23, 2016

Shouldn't be any ground to frame on that, *I think*... any chance at all you got a pair of wires switched?

Steve Frazier · Jul 24, 2016

No chance the wires are switched, like I said before they're color coded and I'm 100% sure they match. Also, the machine ran fine for 2 years after the engine swap and has just started blowing fuses. I started looking at it closer today and have started testing circuits, there's no short showing at the solenoid with the key turned off. Tomorrow I plan to test at the fuse panel and see if I register a short there with and without the key turned on.

Cmark · Jul 24, 2016

OK, I'll have a crack at it.

The fuel shutoff fuse, (I think you're referring to the one on the top left of your fuse box diagram with a line going through a fuel pump?), doesn't have anything to do with the fuel shutdown relay. It feeds the 110-Y1 GN-18 wire to the charge pressure switch. It looks like the machine senses charge pressure to indicate that the engine is running and powers the hold-in windings of the fuel solenoid via the A309-Y4 GY-18 wire. This makes sense with the fuse blowing within several seconds of the machine starting. It would appear to blow once you get charge pressure.

This narrows it down to either;
A) A short circuit to ground in the A309-Y4 GN-18 wire between the charge pressure switch and the fuel solenoid, or
B) A short circuit to ground internally in the fuel solenoid, or
C) The fuel solenoid wired incorrectly.

BTW, I see that you don't have a 3 pin plug to join the solenoid to the harness. In that case don't assume that red-goes-to-red etc. It may do, but it just as well may not do.

Edit: Or D) A short circuit to ground internally in the charge pressure switch.

Cmark · Jul 24, 2016

Here's the full schematic by the way.

View attachment 248_6LZ_1-999_Elec.pdf

caterpillarmech · Jul 24, 2016

It has been several years since I worked on that engine. One hot wire is the pull down and the other is hold. You could have the two hots crossed. One is high amp to pull the solenoid back. The other is lower amp just to hold it while running. That's just off the top of my head. Lots of tractors and time has passed. I had to learn how that solenoid worked on a sunny Friday working at an abandon insane asylum. Just creepy. Nice looking buildings all grown over and completely
silent. All I knew was I did not want to be there anymore!

Steve Frazier · Jul 24, 2016

caterpillarmech, the solenoid I pictured is the one I took out. The new one has the factory plug installed by the factory. Again, the machine was running fine for 2 years after the engine was replaced, this is an issue that just started. Your synopsis of the solenoid is correct, the white lead is the start coil, red is run and black is a dedicated ground for the solenoid.

Cmark, thanks for your input! My guess is "A", the green wire is shorted somewhere since I've replaced the solenoid and the machine worked fine for that length of time. Thanks for the link to the schematic, that will be a big help!! I won't be able to look at it again until this evening and will report back with any findings. It could be something got pinched during engine replacement and it's taken this long to show its head.

seatwarmer · Jul 24, 2016

Tell the story. You know all of us love stories

caterpillarmech said:
It has been several years since I worked on that engine. One hot wire is the pull down and the other is hold. You could have the two hots crossed. One is high amp to pull the solenoid back. The other is lower amp just to hold it while running. That's just off the top of my head. Lots of tractors and time has passed. I had to learn how that solenoid worked on a sunny Friday working at an abandon insane asylum. Just creepy. Nice looking buildings all grown over and completely
silent. All I knew was I did not want to be there anymore!

Steve Frazier · Jul 25, 2016

Did some further testing tonight. I determined which side of the fuse went out to the chassis and used a test light to check for short. I stuck a fuse leg into the energized side of the horn circuit which is live all the time and put the clip end of the test light there. Touched the probe to the chassis side of the fuel fuse socket. No light. Turned key on. No light. Cranked engine. No light. So no light means no ground, no short.

I put a new fuse in the fuel circuit and turned the key on. It didn't pop. I didn't bother to crank because I know from the past the fuse will pop once the engine fires.

It would seem to me that the solenoid is drawing too much power and popping the fuse. I'm thinking that the crank side of the solenoid might not be releasing once the engine fires and overloads the circuit rather than shorting it out. I haven't had a chance to study the schematic in detail, I could be dead wrong.

Steve Frazier · Jul 25, 2016

I just tried something else to verify the connector is wired correctly but it didn't go as planned. I have determined the red wire on the solenoid itself is the run wire so I used the test light again, turned on the machine switch to run to see which pin was energized on the machine connector. None lit the test light! Shouldn't there be power at the pin with the switch turned on?

There's something called a charge pressure switch that seems to be involved in the solenoid circuit but I don't know what that does.

Mark250 · Jul 25, 2016

Steve Frazier said:
There's something called a charge pressure switch that seems to be involved in the solenoid circuit but I don't know what that does.

the charge pressure switch will shut down the engine by disabling the hold in circuit of the solenoid by
a/loss of charge pressure
b/ engine not running
it is a normally open switch that closes with pressure

Mark

Steve Frazier · Jul 25, 2016

OK, so I guess that's why I'm not seeing power at the solenoid connector with the switch turned on.

Cat 248 Fuel Shutoff Short

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