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I have a 2014 z930m EFI that starts to run a bit rough and loses about 50% after mowing for 20-30 minutes. The check engine light does eventually come on, but the code seems non-sensical. Once I turn off the PTO the engine revs back up to normal.

I have replaced coils, fuel filter, checked fuel lines, new spark plugs, and had it at my local JD dealer twice now to no avail.

I've pulled each plug out to see if I could narrow it down to one cylinder, but neither one seems to make a major difference.
Any suggestions?

Possibly EFI high pressure pump not maintaining proper pressure after it gets hot. Would have to have a fuel pressure gauge on the system at time of failure to prove it.

Looks like there are two fuel pumps on this model? Are you talking about #5 or #10 on the diagram below?
I have actually replaced #10 a little while back thinking it might be the culprit.
z930m EFI Diagram

Link not going to the diagram, Just opens the same page as the thread.

Sorry about that, try this one:
z930m EFI Diagram

It is not the mower that is running bad but the engine did I miss something where you posted the kind of engine and model no. I know JD is a SSO and you have to go back through them for parts. But an engine is an engine and may have the same symptoms as other engines of this type on other mowers. Anymore you have to have the soft ware and the different ways to hook it up to a computer to diagnose the problem.

FisherCat930 said:

Looks like there are two fuel pumps on this model? Are you talking about #5 or #10 on the diagram below?
I have actually replaced #10 a little while back thinking it might be the culprit.
z930m EFI Diagram

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#5 which is the EFI fuel pump. That pump is electric and there have been cases where the pump will go goofy and cause low pressure after running for awhile. Will need to be connected to a fuel pressure test kit and see if the pressure drops below normal when then engine acts up. Also if you know what P-code was that would also help.

Once I turn off the PTO the engine revs back up to normal

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Does it bog back down as soon as the PTO is engaged again?

What the fault code the engine is throwing?

sgkent said:

Does it bog back down as soon as the PTO is engaged again?

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Yes

StarTech said:

What the fault code the engine is throwing?

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Last time I took it into the shop they said it was:
0174 - Lean fuel condition at high load (open loop)

Here's one of the plugs. Seems a tad white to me.

Have all the following items?

I am leaning toward a faulty EFI pump. Also keep in mind there is also a filter inside of the EFI pump that is non serviceable, and will clog if the wrong inlet fuel filter has been installed. If I remember correctly the internal filter is a 10 micron, and they recommend a 2 micron inlet filter on the Kohler engine.

There was a case of if I remember correctly it was an older CH26 that would run great for awhile and then loose power and throw engine codes. After running for like an hour the fuel pressure was dropping from 43 psi to 13 psi.

ILENGINE said:

I am leaning toward a faulty EFI pump. Also keep in mind there is also a filter inside of the EFI pump that is non serviceable, and will clog if the wrong inlet fuel filter has been installed. If I remember correctly the internal filter is a 10 micron, and they recommend a 2 micron inlet filter on the Kohler engine.

There was a case of if I remember correctly it was an older CH26 that would run great for awhile and then loose power and throw engine codes. After running for like an hour the fuel pressure was dropping from 43 psi to 13 psi.

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The EFI pump is over $300 so I may resort to getting the $80 knockoff from Amazon just to see if it fixes the problem.. even if only works for a few months.

StarTech said:

Have all the following items?
View attachment 60199

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I'll look into these as well.

Try unplugging the O2 sensor and see how it runs.

If the PTO bogs it down perhaps you have a spindle or other bearing seizing up? Loosen Deck Belt and make sure all blades turn freely. A lean condition may cause backfire.

so the problem doesn't go away when the PTO is disengaged, it merely takes the load off the engine, allowing it to speed up. Maybe as others suggest, post the fault code.

Code 0174 Component: Fuel System Fault: Lean fuel condition Condition: Fuel inlet screen/filter plugged, low pressure at high pressure fuel line, TPS malfunction, shorted connection or faulty sensor. Conclusion: TPS Learn Incorrect ● Lean condition (check oxygen sensor signal with VOA and see Oxygen Sensor). Engine Wiring Harness Related ● Pin circuit wiring or connectors. ECU pin Black 10, 12, 16 and 17. Low Fuel Pressure ● Plugged fi lters. ● Bad lift pump. Oxygen Sensor Related ● Sensor connector or wiring problem. ● Exhaust leak. ● Poor ground. Poor system ground from ECU to engine, causing rich running while indicating lean. Fuel pump module connection. See Fuel Components. Code 0201 Component: Fuel Injector Fault: Injector 1 Circuit Malfunction Condition: Injector damaged or faulty, shorted

Never attempt to disassemble ECU. It is sealed to prevent damage to internal components. Warranty is void if case is opened or tampered with in any way. All operating and control functions within ECU are preset. No internal servicing or readjustment may be performed. If a problem is encountered, and you determine ECU to be faulty, contact your source of supply. ECU pins are coated at factory with a thin layer of electrical grease to prevent fretting and corrosion. Do not attempt to remove grease from ECU pins. Relationship between ECU and throttle position sensor (TPS) is very critical to proper system operation. If TPS or ECU is changed, or mounting position of TPS is altered, appropriate TPS Learn Procedure must be performed to restore synchronization. Any service to ECU, TPS/Throttle Body (including idle speed increase over 300 RPM), or fuel pump module replacement should include ECU Reset. This will clear all trouble codes, all closed loop learned off sets, all max values, and all timers besides permanent hour meter. This system will NOT reset when battery is disconnected! ECU Reset Procedure 1. Turn key/ignition OFF. 2. Install Red wire jumper from Kohler EFI service kit on to service port (connect white wire to black wire in 4 way diagnostic port). 3. Turn key/ignition ON, then OFF and count 10 seconds. 4. Turn key/ignition ON, then OFF and count to 10 seconds a second time. 5. Remove Red wire jumper. Turn key/ignition ON, then OFF and count to 10 seconds a third time. ECU is reset. A TPS Learn Procedure must be performed after ECU Reset. TPS Learn Procedure 1. Turn idle screw clockwise one full turn prior to key/ ignition ON after ECU Reset. 2. Start engine, run at low idle until engine is warm. 3. Idle speed must be above 1500 RPM. If below 1500 RPM, turn idle screw up to 1700 RPM and then shut down engine and perform ECU Reset again. 4. Restart engine, adjust idle speed down to 1500 RPM. Allow engine to dwell at 1500 RPM for about 3 seconds. 5. After this, adjust idle speed to final specified speed setting. 6. Turn key/ignition OFF and count to 10 seconds. Learn procedure is complete.

FisherCat930 said:

Yes

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Only proves that the engine will run at no load even with low fuel pressure. I regularly clean automobile fuel injectors at less than system pressure and the engines will run fine at no load idle. Pressure gauge at injector rail proves it is or isn't fuel pressure related. Doesn't hurt to check fuel volume also. If pressure is in spec, what triggers the injectors? A crank sensor? It would be hard to see a bad crank sensor without a scope, but maybe it would throw a code. The Kohler experts here could comment on that.

Ranchito said:

Only proves that the engine will run at no load even with low fuel pressure. I regularly clean automobile fuel injectors at less than system pressure and the engines will run fine at no load idle. Pressure gauge at injector rail proves it is or isn't fuel pressure related. Doesn't hurt to check fuel volume also. If pressure is in spec, what triggers the injectors? A crank sensor? It would be hard to see a bad crank sensor without a scope, but maybe it would throw a code. The Kohler experts here could comment on that.

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Bad crank position sensor would throw a code also wouldn't fire the plugs or energize the injectors. Basically if the engine doesn't know were it is it doesn't work.

Reading thru the thread this morning.

A couple things I notice one is problem occurs under load so it be an ignition problem under load. Also as mention crank position could have a too large of a gap.

The JD service manual does not cover this problem for the Z930M and I have that manual on my system.

Just a quick followup. I purchased the knockoff EFI pump and mowed with it at full-throttle for about 2hrs yesterday and so far it appears to be running fantastic. It was a little cooler here so we'll see what happens when I mow in the heat next time. I have no expectation that this pump will hold up forever, but for the sake of trying to figuring this issue out I'm pretty happy so far. I also put a new fuel filter on with a smaller micron size as was suggested here.

Gonna see how it does over the next few weeks and will post back with the report. Thanks all!

StarTech said:

Reading thru the thread this morning.

A couple things I notice one is problem occurs under load so it be an ignition problem under load. Also as mention crank position could have a too large of a gap.

The JD service manual does not cover this problem for the Z930M and I have that manual on my system.

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Is the gap adjustable? Was a Mopar problem. Replacement sensor had a paper sticker on the end that set the gap and was wiped away at initial engine crank after replacement.

FisherCat930 said:

Just a quick followup. I purchased the knockoff EFI pump and mowed with it at full-throttle for about 2hrs yesterday and so far it appears to be running fantastic. It was a little cooler here so we'll see what happens when I mow in the heat next time. I have no expectation that this pump will hold up forever, but for the sake of trying to figuring this issue out I'm pretty happy so far. I also put a new fuel filter on with a smaller micron size as was suggested here.

Gonna see how it does over the next few weeks and will post back with the report. Thanks all!

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Tnx for the update and good luck. Just another thing for me to keep in the back of my mind for later troubleshooting when I get an EFI system in.