28 HP EFI Kohler engine. Miss on Number one cylinder.

CHUCK06

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#1
What I have here is a 28hp EFI kohler engine on a GHS Walker mower. The unit is an anniversary special edition, and belonged to someone who only used it for showing it off around his neighborhood. It only has 10 hours of use on it. Both coils are good. Injectors good. fuel good, fuel pressure is good. and plugs are good. compression in No1 is 180psi and No2 170. exhaust temp on no2 around 500 degrees while No1 is around 180. The plug on number one comes out wet though the compression is there and there is a very sufficient amount of ignition. I don't really want to pull this engine out and apart without knowing what im looking for. Anybody who is familiar with these Walker mowers will know that accessing any part of this engine without removal is virtually impossible. Any pointers on this would be very helpful and greatly appreciated. Also note this EFI system is controled by a 32pin plastic cased ECU BOSCH P/N F00HM00010
 

WJR

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#2
Put a new plug in no. 1 and try it.
 

CHUCK06

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#4
Getting ready to pull engine out and apart. I think maybe a valve is sticking once running. though i have only 5% leakdown. hmm. Suppose I'll let you all know what I find.
 

billr

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#5
How consistent is the miss on #1; all the time or just random, or just under certain operating conditions? I know nothing about this engine, so am only trying to throw out ideas before you tear it apart. Is the cylinders inline, opposed, or V? Have you tried swapping coils, swapping injectors? You might even try swapping the injector cables, see if the miss follows the cable or stays with #1. Even with timed injectors, the engine will probably run fairly well if cables are swapped.

Oh, forgot to ask... what is the plug wet with, fuel or oil?
 

CHUCK06

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#6
So far the coils have been swaped with no difference to note, both injectors and intake manifold have been replaced (using new gaskets, torqued to specs) fuel system has a steel fuel rail, which has been cleaned, the miss is consistant, the plug comes out wet with fuel only.
 

CHUCK06

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#8
the cable swap is a good Idea, I just tried that, the miss did not follow
 

billr

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#9
How about trying a vacuum gauge? On engines with more cylinders, a sticking valve will show up as a periodic "ticking" of the gauge needle. A two-cylinder might have too much inherent pulsing on the intake manifold, especially if they are completely separate runners, but it might be worth a try. Is that an even-fire V, with offset crank-pins? With the plug coming out wet with fuel, I'm thinking an ignition problem. Changing/swapping plugs, wires, and coils is a good start, but the coil primary circuit also has to be looked at. What triggers those, direct from the ECM, or is there a separate ignition module? Maybe try a timing light on #1, not so much for timing but just to see if it is intermittent.
 

CHUCK06

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#10
With a vacuume guage the needle consistantly bounces around, the coils get their signal directly from the computer which recieves a signal from the crank position sensor, tps, o2, cyl temp and oil temp. those are really the only sensors on the unit. I spoke to a rep who said this issue happened on another one of the 28hp engines with the same syptoms but since it was so new, an engine replacement was warrantied and I have no way of knowing what was found (if anything) by Kohler, I have been told by one of Kohlers support techs to remove and disassemble the head from the engine and he says I will likely find varnish and such in the valve bore from old fuel being burned, and this unit is out of warranty, but I will likely after following through with this bs, get the engine warrantied through the mower manufacturer as they are genuinly great like that over there. Thank you guys for the help