Cranking but no spark Kohler EFI CH26 78511

fastline

LawnSite Member
I think we examined the schematics before and concluded there were multiple wired grounds. Typically an ECM does not rely on it's chassis to be grounded because it is very common to rubber isolate them for vibration. If it is rubber mounted from the OEM, that should be telling. You could always install a jumper for testing but I doubt that is at issue.

You better hope your mechanic understand electronics. Usually they just swap/install parts until you have a new mower. New ECM, new wire harness, new sensors. etc, etc.
 

65t

LawnSite Member
Location
wisconsin
I think you have pretty much ruled everything else out, chances are the ECU speed input circuit is damaged from the sensor being too close to the flywheel. The voltages generated by the sensor become excessive when it's too close. Most of the parts for the metal ECU system including the ECU are NLA. There was a kit to convert them to plastic 24 755 169-s, it's a little pricey
 

fastline

LawnSite Member
I think you have pretty much ruled everything else out, chances are the ECU speed input circuit is damaged from the sensor being too close to the flywheel. The voltages generated by the sensor become excessive when it's too close.
I just cannot agree with this. Where did this intel come from? This is a Bosch ECU, and they are very good at design. A PG will produce less than 10V and usually 1-2V. There is zero way to exceed those values.

However, the gap becomes important because the rise of the voltage wave is also timing the engine. You can actually advance initial timing by getting it a bit closer.
 

65t

LawnSite Member
Location
wisconsin
There was tech info from Kohler years ago that I can't find right now. That's why the clearance on the sensor is .060". Sure sounds like the ECU is loosing the speed input, likely to not set codes either.
 

fastline

LawnSite Member
There was tech info from Kohler years ago that I can't find right now. That's why the clearance on the sensor is .060". Sure sounds like the ECU is loosing the speed input, likely to not set codes either.
I wish I had more specifics as I would call Bosch engineering and get to the bottom of it. That would be a massive design flaw and 100% ridiculous!

I would agree on speed sense. I think the pins are screwed and I thought about how I would troubleshoot this. The ECU won't even know it is cranking without speed sense, nor would it throw a code. But if it starts pulsing, then stops, it would be flagged because the ECU has a go for ignition 12V signal.

I'd probably just use an inductive spark tester. No sparky if the ECU does not know it is cranking. That means no fuel, no codes, etc. But when you have poor wire connections, results would be sporadic.
 
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Problemmagnet

LawnSite Member
I think you have pretty much ruled everything else out, chances are the ECU speed input circuit is damaged from the sensor being too close to the flywheel. The voltages generated by the sensor become excessive when it's too close. Most of the parts for the metal ECU system including the ECU are NLA. There was a kit to convert them to plastic 24 755 169-s, it's a little pricey
I looked this part up and I would get it if I knew it was compatible. I am pretty sure there is an issue with the ECU but I guess we will see what the mechanic says I'm pretty sure the ecu is bad, but I hope I'm wrong. I haven't found any replacement ECU on Google anywhere. Just a place in Europe that rebuilds them. They will be a while at the mechanic.
 
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Problemmagnet

LawnSite Member
I wish I had more specifics as I would call Bosch engineering and get to the bottom of it. That would be a massive design flaw and 100% ridiculous!

I would agree on speed sense. I think the pins are screwed and I thought about how I would troubleshoot this. The ECU won't even know it is cranking without speed sense, nor would it throw a code. But if it starts pulsing, then stops, it would be flagged because the ECU has a go for ignition 12V signal.

I'd probably just use an inductive spark tester. No sparky if the ECU does not know it is cranking. That means no fuel, no codes, etc. But when you have poor wire connections, results would be sporadic.
Well one thing I know for sure, when I crank, the speed sensor is not getting signal because the MIL light per the manual should turn off when cranking if receiving signal from the speed sensor. Everytime it momentarily starts the light will turn off before it does and that tells me it's directly related to the speed sensor or circuit or something blocking signal. My manual says the speed sensor should be gapped between .20 to .70 but everyone here seems to say .60? Not sure why? I have usually gapped around .30. It may be wrong but I firgure if it's closer it will give better signal and not have any troubles starting. I have done this on 4 wheelers and weedeaters as well. I usually use the lower range of gap.
 
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Problemmagnet

LawnSite Member
So the mechanic has finished looking at it after having it for 4 weeks. They were backed up apparently. They narrowed it down to the ECU causing the issues. They came to the same conclusion that I did, but I was glad to have someone else say it as well instead of missing something simple. I am ordering a metal ecu to plastic ecu conversion kit. Hopefully it's not too confusing to install and I hope it will.be running after I install it.
 
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Problemmagnet

LawnSite Member
I now have done the metal to plastic DCU conversion and now it starts and immediately cuts off still. Could the starter solenoid that holds all the positive wires be the problem? I'm about done with the mower. Now I'm back to a similar issue but at least it starts every time and there are no codes.
 

Nightflyer3

LawnSite Member
Location
Cedar Springs MI
Problem magnet

I've been following your thread because I have the exact same mower. With the metal ecu. No spark, no codes other then 61= end of code. the light never go's out. Meaning no signal from speed sensor. Fuel pump runs when key is turned on. Motor ran great until I rebuilt it after cam failure. My speed sensor tested good ohms. It's putting out 2 to 3 volts when cranking over. Tried. 0060 air gap plus several other air gaps above below it. Voltage dose change alittle with changing gap. I know signal is making it into ecu. Because I opened ecu metal case to check for fried components, water.... everything looks good? (see photos for inside of ecu.? Black mark on board is pin #1) Checked all wires that go to ecu from pins inside ecu for continuity. My mower never had a seat or delay switch that I know of. The other safety switches seem to keep motor from starting. But wouldn't the seat, tip over, and low oil pressure switches stop motor when running? Therefore keep it from running until corrected?
 

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