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SV840 ignition problem.

#1

K

kj4ltc

Last week I noticed my mower with Kohler SV840 was only firing on one cylinder. I checked for fuel, spark, and compression. Found a no spark condition; upon further inspection found a bad wear mark in the plug wire. New coils came in today (Amazon) replaced faulty coil, set air gap. Started mower, still only one cylinder firing, swapped coils - known good coil to cylinder that wasn’t firing. No spark condition now changed to the other cylinder (with new coil). Next I unplugged the white wire (key off). The dead cylinder came alive! But if I reconnect that connector the coil dies out…..so I can run with one wire disconnected, but then have to pull the plug wire to shut it off because the key won’t kill the coil with the white wire unplugged. I’m sure it’s an obvious grounding issue to someone, but HELP


#2

B

bertsmobile1

Kohler coils have diodes inside them to prevent the kill wires interfering with each other.
When you replace Kohler coils it is important to replace both .


#3

Tiger Small Engine

Tiger Small Engine

kj4ltc said:
Last week I noticed my mower with Kohler SV840 was only firing on one cylinder. I checked for fuel, spark, and compression. Found a no spark condition; upon further inspection found a bad wear mark in the plug wire. New coils came in today (Amazon) replaced faulty coil, set air gap. Started mower, still only one cylinder firing, swapped coils - known good coil to cylinder that wasn’t firing. No spark condition now changed to the other cylinder (with new coil). Next I unplugged the white wire (key off). The dead cylinder came alive! But if I reconnect that connector the coil dies out…..so I can run with one wire disconnected, but then have to pull the plug wire to shut it off because the key won’t kill the coil with the white wire unplugged. I’m sure it’s an obvious grounding issue to someone, but HELP
Click to expand...
Notice kj4ltc said coils, plural. Always best to replace coils in pairs, just like shock absorbers.
The coil is mounted to the engine so it is grounded. It has to be a break in the kill wire from coil that won’t shut off to ignition switch. Inspect wire and test and replace as necessary.


#4

StarTech

StarTech

The problem he only replaced the one he thinks was bad when in fact he replaced the good one.

The problem here that when coils are connected the one that is firing is the bad coil. The steering diode is shorted and the killing the other coil. I know goes against most thinking of how something that is working how can it be bad. Kohler solution is to replace both coils at the same time. An alternate method would be to install a Briggs style kill harness, It will last for a while until the coil electronics finish dying which might years down the road. For us with the parts and tools we can make the alternate harness.

At the price of these OEM coils it worth a try anyway.


#5

K

kj4ltc

Tiger Small Engine said:
Notice kj4ltc said coils, plural. Always best to replace coils in pairs, just like shock absorbers.
The coil is mounted to the engine so it is grounded. It has to be a break in the kill wire from coil that won’t shut off to ignition switch. Inspect wire and test and replace as necessary.
Click to expand...
I replaced the kill wire between the 2 coils


#6

K

kj4ltc

bertsmobile1 said:
Kohler coils have diodes inside them to prevent the kill wires interfering with each other.
When you replace Kohler coils it is important to replace both .
Click to expand...
If that’s the case, are the coils side specific?


#7

K

kj4ltc

StarTech said:
The problem he only replaced the one he thinks was bad when in fact he replaced the good one.

The problem here that when coils are connected the one that is firing is the bad coil. The steering diode is shorted and the killing the other coil. I know goes against most thinking of how something that is working how can it be bad. Kohler solution is to replace both coils at the same time. An alternate method would be to install a Briggs style kill harness, It will last for a while until the coil electronics finish dying which might years down the road. For us with the parts and tools we can make the alternate harness.

At the price of these OEM coils it worth a try anyway.
Click to expand...
The presumed bad coil had physical damage to the plug wire, where it had rubbed on something. Not going to say that it’s not possible for the other coil to also be faulty though. I’ll replace the other coil today and see if that helps anything.


#8

ILENGINE

ILENGINE

kj4ltc said:
If that’s the case, are the coils side specific?
Click to expand...
No. But on some engines the kill tab faces up on the #2 cylinder and down on #1. But Kohler made a change with the coils some time back that changed them from a low voltage kill to a high voltage kill, and if the part numbers on the coils don't match the new high voltage kill can cook the old low voltage coil. And it has been my experience that when one coil fails the other one isn't too far behind. Especially on engines that require removal of the engine from the mower to replace the coils. Nothing like pulling an engine, replacing the bad coil get the engine reinstalled and the other coil fails on startup.


#9

StarTech

StarTech

Don't you just hate the way they pack some of engines and other parts in where you got to half take the equipment apart just to replace the bad part. I recently had to pull an engine just to replace the remote starter solenoid. Or like the Gravely I did two weeks ago where the engine had be removed just to replace the main starter cable as a hydraulic hose was in the way and starter could not be removed. All because of a cheap connector Gravely used.


#10

K

kj4ltc

ILENGINE said:
No. But on some engines the kill tab faces up on the #2 cylinder and down on #1. But Kohler made a change with the coils some time back that changed them from a low voltage kill to a high voltage kill, and if the part numbers on the coils don't match the new high voltage kill can cook the old low voltage coil. And it has been my experience that when one coil fails the other one isn't too far behind. Especially on engines that require removal of the engine from the mower to replace the coils. Nothing like pulling an engine, replacing the bad coil get the engine reinstalled and the other coil fails on startup.
Click to expand...
Mine was the old DSAI ignition that had been previously converted to MDI. It only takes a minute or so to access the coils. I’m going to replace the other old one today to see if the steering diode was in fact part of the problem.


#11

ILENGINE

ILENGINE

StarTech said:
Don't you just hate the way they pack some of engines and other parts in where you got to half take the equipment apart just to replace the bad part. I recently had to pull an engine just to replace the remote starter solenoid. Or like the Gravely I did two weeks ago where the engine had be removed just to replace the main starter cable as a hydraulic hose was in the way and starter could not be removed. All because of a cheap connector Gravely used.
Click to expand...
Look at the number of vehicles that require removing the intake manifold to replace the spark plugs.


#12

Hammermechanicman

Hammermechanicman

ILENGINE said:
Look at the number of vehicles that require removing the intake manifold to replace the spark plugs.
Click to expand...
Been there.

Guy wanted me to change starter on a car. It was under the intake manifold.


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