I have a small issue, and I can't seem to find anyone knowledgeable enough to help me understand or be more knowledgeable myself.

I had a problem with a REALLY EASY stalling ATV... no lug warning, sudden, sometimes to the point of an ignition cut it would seem. Never had a really smooth idle either.... always like I could at least feel a very slight miss, and hear a flutter in the engine... and maybe a flutter in something else? Fuel pump? Injector? I dunno..

Well that miss got worse... really really bad.
But never did I get a flashing FI light indicating a problem or stored code.

So I broke out the multimeters (digital & analog) and started crawling over everything I could check without needle adapters or doing controlled temp or pressure tests.

TPS checked out, injector checked out, coil checked out, rectifier checked out, roll-over sensor in place... and so on. Plug looked rich.

In the end the only thing past that I could find was the crank position sensor read out of range on resistance. So I decided I would change that part out of pocket and see if that was it. But then I found out I would have to buy a whole stator assembly to get it. So I just took it in to the shop.

Likewise, they crawled over it and exhausted everything, gave up, put it back together... problem solved. So we assumed it was just a bad connection somewhere that got corrected in the process. So I brought it home, checked the crank sensor myself and it checked fine. So I assumed the bad connection must have been inside under the cover?

Never seemed perfect, just a lot better. Then it sat a lot waiting on upgrades. Added a pipe and it was a whole lot better (but just more power I think). Then sat a long time waiting on protection parts. Cranked regularly, ridden until hot in safe places, etc. No aged gas, etc.

Started riding it more once I got it all together, and I have noticed a decline back to what it was... but without the harsh miss at idle. Slight miss/fluttering and extremely easy to stall. I even dropped a tooth in front, and that's when I realized I had a problem causing the stalling for sure. NOT ME.

I went over what I could again. Plug still looks on the rich side, but better and I find the crank sensor does not ohm out to the resistance it should again. In fact, resistance is lower than before. If I check it hot though, it BARELY makes it in the bottom of the range. I don't know why the difference though?

Bottom line is it stalls chronically... and it's not me. Not even a 50cc 2 stroke stalls like this. It's super weak unless over-revved off the bottom. And when it stalls it comes with no warning. Sometimes like an ignition cut that I can notice more with the lower gearing. The only things that lessen it are the exhaust system and removing the airbox lid. And I am not sure if that's power related or air/fuel related?

But best I understand it, I suspect the ECU might be reading a faulty crank sensor signal... and incorrectly adjusting ignition timing or fuel metering?

Or it could get no pulse or less pulses than required, in which case the ECU would cut ignition?

Or am I barking up the wrong tree suspecting the crank sensor?

Faulty ECU or air temp, coolant temp, or air pressure sensor... that is all that is left... RIGHT?



As a footnote: No, my EFI has never lit even after testing the crank sensor peak voltage... wire disconnected with my meter in the plug while cranking over the engine.... I would think that would trip it, since NO SIGNAL is making it to the ECU during testing.


Any insight is greatly appreciated.

 

Nobody?

 

If you keep ohming out the CAS and it comes back as out of range then I would say you have found your problem. ECUs don't normally like abnormal signals.

 

That's what I think too.


It's that... or it's somehow related to the fact my battery drains unless I park in gear, shut off with key and leave the kill switch on.


That is what I've gathered from everywhere I asked.
That and a few more leads.


If it will ever warm up I have a color coded wiring diagram to go by to do more wiring checks.
Then it goes back to the shop.