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HELP! 500i may get the parts cannon

Ketchup

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Fellas, I could use some help here.

A guy brought me this 500. It pops and dies within 5 seconds. No amount of throttle or priming improves it. Will not pop if throttled while starting.

I’ve been all through the saw. It had some light scoring on the intake side of piston so I replaced that. The decomp was leaking terribly, now plugged. No other leaks. Saw hasn’t seen much use. When I pump the primer more than 6 times fuel leaks from the line where it connects to the injector. Could be the injector is bad, could be the module, could be fuel sensor, could be stator, could be wiring related to any of the above. Replacing all that costs over half the saw.

I had a buddy at the Stihlership plug it in. It’s been started successfully about 800 times, over 3000 failed starts (probably a few hundred from me messing with it). My Stihl friend really didn’t have a good guess.

So where do I go with this? My guess is injector or module, but I don’t know these saws very well. Any insight would be helpful.
 

Brad Krause

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Other than air intake leakage issues fixed by a 1/4" slice of pool noodle placed between the air filter and 1/4-turn cover so the air filter stays fully seated, and water in the fuel causing internal fuel screen issues (located after the fuel filter), didn't the initial 500i saws have injector issues? If so it's possibly a warranty issue within the first 2 years of ownership due to EPA guidelines calling it an emissions-related component. (another thread on the topic)
 
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Ketchup

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I should say MS 500i, not TS 500i. Similar design but the parts do not interchange. The injector on a TS is more serviceable, but I’ve been through this MS injector. It’s clean. No visible problems.

It’s past the two year mark, I believe.
 

Ketchup

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I don’t think it’s supposed to be leaking fuel when pressing the primer bulb twenty times. Let alone six.

That’s why I mentioned it, but I’m not sure how much that tells me. I may just be over pressurizing the supply line.

Another clue is that I get a little more run time if I pour a shot of fuel past the throttle butterfly. My figuring is that the pump isn’t supplying fuel.
 

Maintenance Chief

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That’s why I mentioned it, but I’m not sure how much that tells me. I may just be over pressurizing the supply line.

Another clue is that I get a little more run time if I pour a shot of fuel past the throttle butterfly. My figuring is that the pump isn’t supplying fuel.
Delete the primer button, as in join the two fuel lines together if you can . That would at least eliminate one potential problem.
 

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That’s why I mentioned it, but I’m not sure how much that tells me. I may just be over pressurizing the supply line.

Another clue is that I get a little more run time if I pour a shot of fuel past the throttle butterfly. My figuring is that the pump isn’t supplying fuel.
I don't know anything about the 500i, and little about others. The primer bulb should never cause a leak. If you can make one with a primer bulb, it is either a real crappy design,(unlikely), or there is something wrong! Someone knows more about this saw than I do,(not hard to do), that can set me straight if this is the correct behavior.
 

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500i has an unusual primer. It doesn’t pull fuel through the carb because there is no carb. It pulls fuel from the tank and pushes it into the barrel of the injector. But the injector has to move to let fuel into the intake. It doesn’t open unless the module tells it to open. Pushing the primer just adds pressure to the line. But it does seem wrong that it would leak out around the nipple instead of return to the tank.

Fingers crossed the injector is bad. I ordered a new one.
 

thompsoncustom

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500i has an unusual primer. It doesn’t pull fuel through the carb because there is no carb. It pulls fuel from the tank and pushes it into the barrel of the injector. But the injector has to move to let fuel into the intake. It doesn’t open unless the module tells it to open. Pushing the primer just adds pressure to the line. But it does seem wrong that it would leak out around the nipple instead of return to the tank.

Fingers crossed the injector is bad. I ordered a new one.
any way to test the injector? you said the module is what tells it to open so could you send X amount of volts to the injector and see how it sprays or if it's sticking open?
 
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Mastermind

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Following.

Out of 150 or so of these that I've ported, only one that I'm aware of had a serious problem. It turned out to be a bad module. Was sent to Virginia Beach and replaced under warranty.

The dealer should contact his rep, and make them aware of the issue. Stihl might want to take a look at it.
 

Ketchup

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any way to test the injector? you said the module is what tells it to open so could you send X amount of volts to the injector and see how it sprays or if it's sticking open?

That’s definitely something I wonder about. I read somewhere the voltage of the Mtronic system is pretty unusual. The injector looks relatively similar to an Mtronic solenoid, but larger. Based on the gauge of the wiring, the Voltage is probably pretty low. I was reluctant to experiment there, but when I swap the part I’ll see what I can figure out.

In this case I believe the injector is stuck closed, not open. The TS500i can have flooding problems related to the injector sticking open. But the only time this saw runs is when I intentionally flood it.

With that in mind, I don’t really understand why the saw will pop but not run. It tries to start on almost every single pull. I feel like there must be a tiny bit of fuel getting through as part of the start cycle, but the run cycle isn’t functioning. That points to the module rather than the injector. I hope it’s not that because software is required to replace the module.
 

Mastermind

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That’s definitely something I wonder about. I read somewhere the voltage of the Mtronic system is pretty unusual. The injector looks relatively similar to an Mtronic solenoid, but larger. Based on the gauge of the wiring, the Voltage is probably pretty low. I was reluctant to experiment there, but when I swap the part I’ll see what I can figure out.

In this case I believe the injector is stuck closed, not open. The TS500i can have flooding problems related to the injector sticking open. But the only time this saw runs is when I intentionally flood it.

With that in mind, I don’t really understand why the saw will pop but not run. It tries to start on almost every single pull. I feel like there must be a tiny bit of fuel getting through as part of the start cycle, but the run cycle isn’t functioning. That points to the module rather than the injector. I hope it’s not that because software is required to replace the module.
Do you have an MDG?
 

Crocky28

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also following. Interested to know how you get on.
 

Stump Shot

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500i has an unusual primer. It doesn’t pull fuel through the carb because there is no carb. It pulls fuel from the tank and pushes it into the barrel of the injector. But the injector has to move to let fuel into the intake. It doesn’t open unless the module tells it to open. Pushing the primer just adds pressure to the line. But it does seem wrong that it would leak out around the nipple instead of return to the tank.

Fingers crossed the injector is bad. I ordered a new one.
This is more of a question than a statement, if the primer can leak out when operated, could it not suck air when running?
 

Mastermind

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is there only one MDG is this the part number? 5910 840 0210. Does this come with everything you need or is there more to order?
That's the one I have. If I'm not mistaken there are additional cables that are needed to attach it to the 500i. I got mine used from a friend.
 
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