7520 strange starting behavior

[jrchafin]

My 7520 is acting up. It's 10 years old. One day after running fine the previous day I went to start it and it cranked and cranked but wouldn't start. Grey smoke coming out of exhaust. I tried a few more times and then right as I released the key (giving up), it started. Ran great.

This has happened several times now. When I go to start it, it cranks with grey smoke, but won't start. Occasionally while cranking it will fire, maybe sputter a bit, but won't start. Then after a few tries, just as I release the key it starts and runs perfectly. It will not start while cranking, but only right as I release the key. Seems to me there must be something electrical that is preventing it from running while the starter is cranking.

Yesterday as I was finishing up, it was running great and I shut it down. As a test, I tried to restart it, and the same thing happened. Won't start while cranking, but only when I release the key.

No diesel mechanic am I. Is there something obvious that would be causing this?

Thanks,
Jon

 

[xtxpete]

Hmmm, that seems strange! How is the battery? Is it still cranking it over as well as it once did? Does the fuel pump have a lift pump in the tank that you can hear running? Is there a fuel shutoff solenoid on the injector pump that's not opening while it's got the starter load from turning it over and then when you release the key it gets the volts it needs and opens and the inertia of the engine starts it? Lots of questions

 

[jrchafin]

It seems to crank normally, so I assume the battery is ok. I'm not sure about the lift pump. Is that something I would hear only when the starter is cranking? Or just when the key is on? The fuel shutoff is a good idea. I wonder though, doesn't the grey smoke indicate fuel getting to the engine? Do you know if the 7520 has a lift pump or not?

 

[xtxpete]

I don't know if it would have a lift pump, but it would be heard with key on. If it smokes all the time while cranking, then yes, it must be getting at least some fuel!

 

[Leejohn]

I would start at the key switch !

 

[xtxpete]

It seems to crank normally, so I assume the battery is ok. I'm not sure about the lift pump. Is that something I would hear only when the starter is cranking? Or just when the key is on? The fuel shutoff is a good idea. I wonder though, doesn't the grey smoke indicate fuel getting to the engine? Do you know if the 7520 has a lift pump or not?

Is your tractor still working the same way, or have you found a problem?:confused3:

 

[tommyo7]

They don't have a separate lift pump its part of the injection pump. if you keep the tank full or park nose down on a hill it will get fuel right away. If it is smoking it is the electrical system, i havent cured mine yet but I suspect the glow plug circuit some where. like said above start with the ignition switch. Mine has bad glow plugs, problem being Mahindara parts are ridiculous they want 900+ for new plugs, I have to find a cross reference somewhere if someone has any info I would greatly appreciate it.

 

[xtxpete]

I would tend to think if it's just glow plugs, then it would start just fine when starting right after shutting it down!

 

[bindian]

JR,
Did you find the problem?
hugs, Brandi

 

[xtxpete]

Jon, has this problem been resolved? You leave us wondering what you found if it is!

 

[jrchafin]

Sorry for the delay everybody. Apparently I need to change my notifications so I know when somebody has replied to me! The problem hasn't been resolved, but I have figured it out a bit more. The fuel shutoff solenoid is not getting power while the starter is cranking, but gets power when the key is on or the tractor is running. I rigged up a test light so I could see what it's doing. In the warm weather, it's been working to just crank it a few times and as soon as I let off of the key, the solenoid opens and the tractor starts up. A mechanic friend of mine said that often the circuit supplying voltage to that solenoid during cranking is a completely different circuit than while it's running, so figuring out where the problem is could be tricky. But he's not a tractor mechanic, so who knows if he's right. One day I need to get out the wiring diagram and trace the whole starting circuit to see what might be the problem. Hopefully just a simple relay.

 

[xtxpete]

Hey, better late than never! Well it sounds like you're on the right track to get that sorted out!