Stihl TS500i Fuel Pump Tech Tip....

[alexcagle]

I'll post this here in chainsaws, since it will apply to the new MS500 chainsaw.
I just recently had a TS500i that was a bit if a head scratcher, and finally tracked down why it was suffering significant power loss after about a full minute of cutting.
I've never had a single issue with one of the primer/ fuel pump modules.....until now. This out of hundreds of TS500i's.
It had a tiny crack in the diaphragm of the pump, which was the culprit.
Pressure test at the fuel pickup hose, held pressure to 10psi, which was because of the inlet needle inside the module, which isolates any back pressure.
Long story short.....
If you have a problem with;
*Fuel pooling inside the crankcase, coming out of the muffler, which is also a more common trait of a leaking (bad) injector after shutdown.
*You have to hold the throttle wide open to get it to start. Then smokes a lot.
When you pull the left most hose off the pump to pressure test the injector.
Which, by the way is:
After pumping up to around 5psi and bypassing, then it should drop to about 2.5psi and hold. If it continues to leak down, then the injector is bad.
Fuel pump/primer test;
Pull the impulse hose off (the center hose), at the fuel pump/primer module.
If you see any fuel spray out when you pump it, then your pump diaphragm is ruptured, and needs replaced.
It's cheaper to just replace the pump entirely from Stihl.

 

[pioneerguy600]

Thanks for the info, archived for future reference if needed.

 

[DND 9000]

@alexcagle very good information, thank you. Do you know which diaphragm is in there? Do you have a name or a part no for it?

 

[alexcagle]

@alexcagle very good information, thank you. Do you know which diaphragm is in there? Do you have a name or a part no for it?

I'm not sure if they offer replacement diaphragm parts, but it looks like a specially designed Zama unit. Though it is easy to take apart.
I think they are cost effective to just replace. I seem to remember raising an eyebrow as to how inexpensive they were.....
-a fraction of the rediculously expensive injector's cost.

 

[alexcagle]

I've covered this in another post; But I'll post it here again.
If your primer bulb is really slow to retract, then it's a good chance your internal injector screen is partially plugged up. I would replace the fuel filter first, to rule out that possible restriction issue.
The inlet barb is removeable by twisting and pulling. The tiny screen is behind it, and I personally just discard them.
*
Here is another older post with more TS500i info, tips, etc....https://www.arboristsite.com/commun...hl-ts500i-injector-apart.307486/#post-6307262

 

[alexcagle]

Here is the tiny leak in the pump diaphragm.

Here are the components.

 

[DND 9000]

Thank you for your answer, good to know.

 

[PogoInTheWoods]

Thread bookmarked. Good stuff. Thank you.

 

[alexcagle]

UPDATE:
Due to the fact that EPA now rules that any wetted hose be replaced when disconnected, for what ever reason that may be.....
The fuel pump module is significantly more expensive, because it comes with the new injector hoses included.
I think it's in the mid $50 dollar range now.

 

[ted willams]

this site holds the best real world info on the ts500 that ive seen yet. Ive recently picked up a 2nd hand ts500 which started and ran great. about two wks later would not start. put new fuel, plug and all new filters in and still no start. so I tried the socket and drill trick after I got tired of pulling and within a half a second it started. ran it till it was warm, shut it off and nothing, would not start by pulling however started right up with the drill turning it over. any thoughts would be appreciated and thank you in advance.