Help understanding sensor impacts on ECU
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Author:  Smoker [ Thu Dec 06, 2018 4:00 am ]
Post subject:  Help understanding sensor impacts on ECU

I have a 2 stroke EFI dirt bike from a european manufacturer. First year for their EFI bike. They have sold thousands and 95% of the owners love them, they are great. However, the other 5% have lemons. The run rough off idle and rich until hitting "the pipe", and then take of and run like a banshee. The runs that run well are smooth and quite linear.

For those who have "lemons" we dont get much support (if any) from the manufacturer as these are race bikes and have a really short warranty. We have tried dozens of things to try and fix it without any luck. ECU replacement, spark plugs, new fuel, replacing sensors, replacing TPS, TPS adjustment, replacing injectors, pull a sensor at a time. etc etc. You name it we have done it.

OK I am not here for you to help fix the bike, but I am asking to help understand how sensors can affect the ECU.

The bike is simple. Open loop, Alpha-N. No O2 sensor. Injectors are in the transfer ports (a bit further along than the throttle body). It has the following sensors:

Crank position sensor CPS
Intake Air Temp IAT
Coolant Temp CLT
Crankcase pressure sensor CPS

and for output:

Bosch injectors
IDI ignition

What I would like to understand - in general - how do these sensors typically affect fueling and ignition? I have programmed EFI bikes and do understand the basics of mapping.

TPS is obvious as it forms part of the map, if it is messed up we would be getting bad fueling and bad ignition.
CPS helps with RPM and ignition advance
CLT I am guessing it really is only used to determine if it should run the idle circuit or not
IAT ???
CPS is interesting. I am guessing is is used as some sort of MAP sensor, taking it form the crankcase rather than the manifold. Perhaps because dirt bike manifold do not produce enough vacuum? I am sure there would have to be a bit of timing for the sampling as every cycle the crankcase can get under pressure, when the transfer ports close (I think).

Anyways, any enlightenment would be appreciated.

Author:  Fred [ Sat Dec 08, 2018 11:02 am ]
Post subject:  Re: Help understanding sensor impacts on ECU

TPS, correct, and maybe transient fueling too, ie, when you jump on it, dish out a bit more to make up for various things
CPS, correct, RPM and position/angle info so firing the plugs can be the right angle
CLT, idle valves, but mainly mixture, rich when cold, normal when hot, could be your issue, pig rich?
IAT, density info, correction over the Alpha-N perhaps, like CLT, can drastically affect fueling, hotter reading = less dense air in model, less fuel delivered, and leaner running if the air isn't really hot, and vice versa

CPS based MAP sampling is certainly possible, but you didn't say it had a MAP sensor?

Hope that helps, welcome to the forum! :-)

Author:  Smoker [ Sat Dec 08, 2018 3:12 pm ]
Post subject:  Re: Help understanding sensor impacts on ECU

Thanks Fred,

Oops - I made a mistake in my acronyms.

It has no MAP or MAF. It only has a crankcase pressure sensor. It measures air pressure inside the crankcase. In a two stroke this is where the air/fuel goes before being pushed into the cylinder. I suspect they are using this sensor as the "MAP" sensor.

Author:  Fred [ Mon Dec 10, 2018 9:58 am ]
Post subject:  Re: Help understanding sensor impacts on ECU

Very interesting, as MAP, or most likely as AN correction of some sort? Could go either way depending on how you look at it and how the math is. For some 4 stroke engine setups MAP is an entirely unreliable indicator depending on RPM. For those you have to use AN at least in the lower ranges.

Care to post a picture of the bike in question and/or the running gear and/or ECU? I'm curious now :-)

Author:  Smoker [ Mon Dec 10, 2018 3:31 pm ]
Post subject:  Re: Help understanding sensor impacts on ECU

Sure no problem, although I dont think it will help much - it is a completely closed system.

It is the KTM/Husky 2018/2019 250/300 TPI bikes. It uses the Synerject M3C ECU.

Here is a more technical article on it: ... 9EOjZD4.97

I have replaced the ECU with a GET ECU that allows me to program maps and read sensor values.

OK, on another note.

I tested the IAT using the ECU software comparing it to a high accuracy temp probe. It was within a degree from 15 deg C to 45 deg C.

I tested the CLT using the ECU software and it was reading 7-10 deg C high - would this be a problem?

I tested the TPS using the ECU software comparing it to marks on the throttle body - really just checking for linearity as I can program range. It tested good.

Next I need to test the crankcase pressure sensor. CCP.

Author:  Fred [ Sat Dec 22, 2018 10:17 pm ]
Post subject:  Re: Help understanding sensor impacts on ECU

7-10 high would just make warm up a bit leaner, most likely.

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