Cranking but no spark Kohler EFI CH26 78511

Problemmagnet

LawnSite Member
I am at my witts end with this mower. A little backstory. I rebuilt the mower six months ago and it has been running great and a couple weeks ago I was mowing and it stuttered and then backfired so I parked it and check things out and tried to start it back up and no spark to the spark plugs so I checked and checked and eventually checked the crankshaft sensor or speed sensor whatever you want to call it and it had came loose from its bracket and the flywheel head-worn a Groove into it so I assumed that it was bad and I replaced it with a very hard to find sensor that looked the same was the same length and same size but it was a Duralast crankshaft position sensor. The one that I had removed was a Bosch sensor and did not look to be the original sensor. Both had ohm readings over 900 and the manual calls for something like 325 to 395. So I installed the new sensor and still no fire to the coils when cranking. Also the MIL light stays on when cranking witch the Manual flow chart says that the crankshaft position sensor is the problem. However, it's new, but it could be a bad part or just wrong for the engine possibly. Also I tested the voltage at the sensor harness with the key on and it is only reading 2.26 volts. Should it be reading 12v? If so, does that mean that my ECU is bad? I should state also that I have checked all of the grounds and fuses and they seem fine. Also the fuel pump works and it cranks just fine. There is just not spark and I assumed it was just the sensor that was the problem but could it rubbing agains the flywheel cause a surge of energy to ruin the ecu? I really am lost atm. I also turned the key 3 times to get a code and what I am getting is a 2242 code which is not in the manual and adds even more questions unfortunately. I do not have a diagnostic hookup, which would be extremely useful but so overpriced.

UPDATE
I have checked all of my safety switches and they all seem to be functioning as designed. Also, I do not know how to test the seat delay module which I think also controls my left and right control arm interlock safety switches. I may just change it just for good measure. I have also ordered the correct speed sensor part and am awaiting that. I would appreciate if someone would let me know where the coil kill switch or kill wire is 2 help out or possibly disconnect to see if that will allow fire. Hoping it's just the crank sensor but I have the worst luck.

Exmark lazer z efi model number 256084
Kohler ch26 78511
 

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fastline

LawnSite Member
Sensors like this are typically 5V but sometimes 12V. Never 2.26V. What I have experienced is a short in a system that will either draw down the 5V source voltage, or in one case destroyed the 5V power IC internally in an ECU in which I did a board level repair. I don't recommend that type of repair unless have electronic experience.

You may want to unplug other sensors and see if the voltage returns to normal. In many cases, an ECU sensor voltage output is current limited for good reason so having some voltage is hopeful. If another sensor or wire is shorting, that will cause too much current to be drawn.

The codes from the ECU will help determine if there is a systemic issue. In my one example, I had about every sensor code because sensors were not receiving proper voltage. I would explain how I found and fixed that issue but it gets deep.

I recommend you look up the specs from the model of sensor you have and determine what the reference voltage should be.
 
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Problemmagnet

LawnSite Member
Thank you for your help. I would love to be able to look up what the reference voltage would be but I have no clue where to find it it's not in the manual and it's not in any other manual that I know of. When turning the key three times I only received the end sequence for codes and I don't receive any codes anymore. For a short time I receive a 2242 code which is not in the manual so that didn't answer any questions. And I do not have a code reader. I am just reading the lights that go off the MIL. I'm still waiting on the sensor to get back I have ordered the safety module because I tested all sensors and every one of them checked out I tested all the relays and every one of them checked out it's looking like if I really have an issue after I get everything back together it's likely something in the ECU. Wondering where a short in the line could be? Like I said the only thing that happened was that the crank sensor bracket came loose and the crank sensor was making contact the flywheel that's all that happened but this cause major issues somewhere else suddenly? Also does the crank sensor ground onto the bracket which is connected to the crankcase or does the grounding have to do with the wiring harness on it?
 

JoeRagMan

LawnSite Senior Member
Location
Near TMI
Looking at the Kohler manual, the ECH fuel injection system requires a minimum of 6 volts to operate. The manual has a pin out of the ECU connector which you could test for powers and grounds with a volt/ ohm meter. Possibly the power connection in the speed sensor got grounded when the physical damage happened and damaged the ECU?
Do you know which EFI system is on your machine?
 

65t

LawnSite Member
Location
wisconsin
CH26 is a Bosch injection system. You said the fuel pump runs...does it run only for a few seconds when turning the key on? Check to see if its running when cranking. When the engine is running or cranking--flywheel in motion--the ECU will turn the fuel pump on. If it runs during cranking, the ECU is getting a signal from the crank position sensor and your lack of spark problem is probably safety system related. Hate to say it, but I've seen when the crank position sensor to flywheel is too close, it induces excessive signal voltage and destroys the ECU, that's why that clearance setting between the sensor and flywheel is set to .060"
 

fastline

LawnSite Member
Look at your old sensor, look for numbers, and google all that! See if you can find the data sheet for it and post that! Also post a 'clear' schematic for the ECU and related sensors.

Sensors work in many different ways. Some do not need source power at all, some need very clean and perfect 5V. Your odd voltage is very telling. Usually 5V sensors are fed from a "common source", which means there might be different wires coming from the ECU to each sensor, but they all are ultimately fed from one place in the ECU. If one of them is grounded, there is an issue.

Not to be confrontational, but I don't buy getting a sensor too close and damaging the ECU. Most auto sensors are digital which means there is just an 'on' and an 'off'. Return voltage triggers can never exceed the source voltage so that is a design parameter. But possible physical damage shorted the source rail and the ECU was protected from such shorts, which I would find odd from Bosch. They know better.

As I have stated, unplug some sensors and see if the voltage returns. When you turn the key on, you should get voltage to sensors.

In my case with a bad Ford ECU, I quickly determined there was a short, but that short was in the ECU!!! That was an intense surgery..... In your case, if we find that sensors need 5V, and you unplug sensors and never get that voltage, you will need an ECU.

Here is another test if you have a meter. this will require a DMM in amps, not a clamp meter. Find the ground wire to the ECU and get your meter in series with that so you can read the amps. With just the key on, it should not pull much power at all. You can report your finding and we can examine that. In my case, I think the Ford ECU was pulling like 5A and connected to nothing! My experience told me something was shorted.
 
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fastline

LawnSite Member
Thanks! That is hugely helpful and we are chasing the tail! That system uses a typical "inductive pickup coil". that is a 2 wire, not powered device! The sensor can also be simply tested. One test is the coil resistance. They use an internal magnet to induce an AC voltage and a hysteresis trip circuit in the ECU. You can literally unplug that sensor when mounted, connect a DMM in VAC to the sensor and crank the engine. You should see a voltage. That value will be erroneous as only a scope could see the wave form and peak voltage.

What this further means is it is impossible to "short" that and cause an ECU issue unless it was somehow shorted to a voltage source. Lets get a new sensor in there, gap it, and see what happens.
 
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Problemmagnet

LawnSite Member
Lots of good information that I can go check pretty soon here it's raining unfortunately right now and it's outside because I can't get it in LOL. However my speed or crank sensor is a three-prong and not a two prong I was just spitballing to think that it could somehow damaged the EC you but this was my experience that this fell onto the flywheel and cause it to backfire and run oddly and then never started back up because it was never getting fire and then I only found out later that it was getting a two and a half volt signal rather than 5 volts. I will try to unplug other sensors and check the voltage will I need to bypass the sensors I unplugged? Or should I see a difference as soon as I unplug it? Also wondering if my oil temp sensor could be causing these issues? I do have a voltmeter though I am not an expert by any means when it comes to diagnosing electrical problems it's all a learning process for me but I can say without a doubt that the engine itself is in perfect shape but this electrical issue is killing me and it would be my luck that it is the ECU. I'm not sure if this is just an example of an oldie see you or how they all smell but when I unplug my ACU I can smell pretty strongly electrical components smell not necessarily burning but it could have been from an old burn or blow out of something in the ECU. But that is just me guessing at this point.
 
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Problemmagnet

LawnSite Member
As far as the fuel pump it does turn on when I turn the key on I do not know if it runs when I crank as I cannot hear it over the cranking but I can test for that as well. I can say I don't think it's shooting gas through the injectors as I crank because I haven't smelled any gas on the end of the spark plugs.
 

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