Engine backfires and now takes a big battery to turn over

Old 09-21-13, 04:07 PM
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Engine backfires and now takes a big battery to turn over

I have a Lazer Z mower with a Kohler EFI Command CH18-750 engine. I got this used 5 or 6 years ago. Had a bad computer in it and I ended up replacing the computer a second time. Local dealer kept it all summer last year so will not be taking it back to them. IT has been occasionally backfiring when mowing and now requires me to use a high cranking capacity battery to get it to turn over and start. It may have a short somewhere since the battery in the past has often been too low to start it without charging it. I assumed it was a short and started disconnecting the battery after each use, but now I must charge the battery often. I am guessing timing or bad valves, but hate to start dismantling it without some testing first.
Old 09-21-13, 07:00 PM
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Had the battery load tested after fully charging?
Simple enough to check timing and for a valve problem.
Back firing while it's running has nothing to do with the battery. More likely a carburetor problem.
When's the last time it's been rebuilt.
Old 09-21-13, 11:18 PM
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I'm not very familiar with those engines yet. i would be suspecting a bad crankshaft position sensor.
Old 09-22-13, 06:48 AM
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Hello roberte6,

First I want to say, It sounds like you have two issues going on.

The need for a higher amp battery sounds like you have a starter issue, Possibly a tear-down cleaning and re-lube would help....

The battery needing charged sounds like the charging system isn't functioning properly, This could account for the backfiring. The ECU (computer) MUST have at least 10.5 continuous volts to operate properly, If a charging system isn't putting out proper voltage it doesn't take long running a electric PTO clutch to drop the voltage below the 10.5 spec and cause run issues.

Another thing I want to mention is...... Charging a battery on a EFI machine with the cables hooked up is a BIG no no, ALWAYS remove at least one battery cable before charging..... The same applies with jump starting a EFI machine from another vehicle.....Otherwise damage can be done to the ECU......

I suggest performing a charging system test, Here's a copy/paste from one of my previous post;

Charging System Operational Inspection •Check the battery condition.
○Always check the battery condition before judging other
parts of the charging system. The battery must be fully
charged for accurate charging system tests.
•Warm up the engine to bring the components up to their
normal operating temperatures. •Measure regulated output voltage at various engine
○Connect a voltmeter across the battery terminals.
The readings should show nearly battery voltage when
the engine speed is low, and as the engine speed rises,
the readings should also rise. But they must stay within
the specified range.
If the output voltage is much higher than the specification,
the regulator is defective, or the regulator leads are loose
or open.
If the output voltage dose not rise as the engine speed
increase, the regulator is defective or the alternator output
is insufficient for the loads.
Regulated Output Voltage
Battery Voltage to 15 VDC

A EFI machine does have a continuous draw on the battery, The ECU uses power to maintain all the proper run settings..... It's in memory mode when not running, But if left sitting for close to a month without being cranked it will drain the battery low enough to cause start issues.

Perform the above test, If you find a charging system issue shout back for further testing procedures....

Good Luck

Last edited by cheese; 09-22-13 at 10:32 PM.

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