721D Starts but doesn't run... Fuel solenoid problem.

mallard

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
Hey all,

I recently got a 2002 721D mower, and it worked great for the first few cuts. A while back, however, it died on me while it was running and refused to start. It would catch and fire for a second, but then the engine would die. I quickly traced this behaviour to the fuel solenoid not staying open when the key was in the run position, and only opening when turned to "start."

My first thought was that the solenoid was bad. I bought a new one and replaced it. No change.

I traced the cables back to a "switch interlock," and thought for sure that my problem lay there. I bought and replaced the switch interlock, and nothing changed. At this point I realized that my voltage regulator was bad, because if I held the fuel solenoid open by hand and ran the engine, I got no voltage and a battery light, but I'd confirmed that the alternator itself was producing voltage. I don't believe this was the root problem, and I think I caused this by using the incorrect fuse on accident, but it definitely died.

I replaced the regulator, and the mower now makes proper voltage, but it still won't run on its own.

At this point I'm completely lost. I've attached a wiring diagram below, and I don't really know what to make of it. There's a distribution plate of sorts that runs to pretty much everything, but I've confirmed that the two pads that run to the switch interlock both have voltage when the key is in the run position. I've confirmed that I have voltage across the connector to the switch interlock, but the mower still won't run.

I've checked all of the fuses, checked the two solenoids under the dash, and I'm 90% sure that the ignition switch is working properly. There are only 5 terminals, and it seems that only 1 of them is ignition power. And being that all the lights and gauges work, I know that I'm getting power.

One interesting thing I saw on the wiring diagram is that one wire in the fuse box literally leads to an empty fuse socket. There's nothing else there. This is depicted on the diagram, and my actual mower is wired this way as well. I'm not sure what that's supposed to accomplish, but it's obviously the way it's meant to be, so I didn't think about it too much.

Does anyone have any ideas on how to fix this? I'm completely stumped. I'm about 3 days away from doing away with the solenoid altogether and adding a manual lever to open and close the fuel valve.

I'd really appreciate any advice.
 

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tew45

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
I also have that problem. It is the holding voltage that holds the fuel solenoid open while running. I don't know where it comes from or I would fix the problem. Now I just have a strap around the fuel solenoid then start it and leave it connected while mowing then remove it when I stop. Sometimes it will keep running without the strap on. It seems like an intermittent connection could be the cause. I will ask where the holding voltage comes fron and I think I will repair it then.
 

tew45

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
Hey all,

I recently got a 2002 721D mower, and it worked great for the first few cuts. A while back, however, it died on me while it was running and refused to start. It would catch and fire for a second, but then the engine would die. I quickly traced this behaviour to the fuel solenoid not staying open when the key was in the run position, and only opening when turned to "start."

My first thought was that the solenoid was bad. I bought a new one and replaced it. No change.

I traced the cables back to a "switch interlock," and thought for sure that my problem lay there. I bought and replaced the switch interlock, and nothing changed. At this point I realized that my voltage regulator was bad, because if I held the fuel solenoid open by hand and ran the engine, I got no voltage and a battery light, but I'd confirmed that the alternator itself was producing voltage. I don't believe this was the root problem, and I think I caused this by using the incorrect fuse on accident, but it definitely died.

I replaced the regulator, and the mower now makes proper voltage, but it still won't run on its own.

At this point I'm completely lost. I've attached a wiring diagram below, and I don't really know what to make of it. There's a distribution plate of sorts that runs to pretty much everything, but I've confirmed that the two pads that run to the switch interlock both have voltage when the key is in the run position. I've confirmed that I have voltage across the connector to the switch interlock, but the mower still won't run.

I've checked all of the fuses, checked the two solenoids under the dash, and I'm 90% sure that the ignition switch is working properly. There are only 5 terminals, and it seems that only 1 of them is ignition power. And being that all the lights and gauges work, I know that I'm getting power.

One interesting thing I saw on the wiring diagram is that one wire in the fuse box literally leads to an empty fuse socket. There's nothing else there. This is depicted on the diagram, and my actual mower is wired this way as well. I'm not sure what that's supposed to accomplish, but it's obviously the way it's meant to be, so I didn't think about it too much.

Does anyone have any ideas on how to fix this? I'm completely stumped. I'm about 3 days away from doing away with the solenoid altogether and adding a manual lever to open and close the fuel valve.

I'd really appreciate any advice.
The fuel hold on voltage comes from the switch interlock module and it costs over $62.00 so I will just keep using a manual strap when mowing!!!!!
 

bertsmobile1

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
If you have power to the solenoid in the start position & not in the run position then I would be looking at the ignition switch .
Unfortunately that wiring diagram is not readable .
 

StarTech

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
1642972359211.png1642972434012.png
 

tew45

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
If you have power to the solenoid in the start position & not in the run position then I would be looking at the ignition switch .
Unfortunately that wiring diagram is not readable .
I have the same problem sonetimes and when I DO i just tie the fuel shutoff valve open and remove it when I stop sometimes it works properly especialty when the battery is fiull power.
 

tew45

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  • / 721D Starts but doesn't run... Fuel solenoid problem.
I have the same problem sonetimes and when I DO i just tie the fuel shutoff valve open and remove it when I stop sometimes it works properly especialty when the battery is fiull power.
 
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