here - By 3RZ
I would recommend that
you stay with resistor type spark plugs if specified by the manufacturer.
It seems that the resistor inside the plug is used as part of the
resistance of the driver circuit of the ECU in the newer ECU/EFI
vehicles. (It was orginally introduced to suppress radio interference)
Using non resistor plugs cause the drivers in the ECU to overheat
and get damaged because of the lower resistance. This little lesson
cost me R4400 compliments of Renault for a new ECU. I got the wrong
alternative spark plug part no of a website and when the spares
shop did not have the correct one's in stock used NGK BP6ES's instead
of BKR6E or BKR6ES. An expensive mistake I will not make again.
From the NGK website:
An engine converted from
petrol to L.P.G. (liquefied petroleum gas) will cause a change in
the spark plug operating conditions. Therefore, some consideration
should be made on the type of spark plug being installed.
As L.P.G. has different
properties to petrol it influences the spark plug operating temperature
and required voltage. The extent of this influence can be seen when
comparisons are made on spark plugs which were fitted in an engine
using L.P.G. and petrol.
Typical results are as
1. Spark Plug Temperature
Temperatures are higher
compared to petrol. This occurs due
to L.P.G.'s reduced cooling effect.
2. Spark Plug Required
Required voltage increases
because of the difference in the bonding
of gas particles between the two fuels.
To eliminate the influence
of L.P.G. and to obtain optimum spark plug performance, NGK recommends:
-The use of a spark plug
with one heat range colder (if possible) than that listed in the
catalogue: eg, BPR6EFS-13 (L.P.G.) instead of BPR5EFS-13 (petrol)
for VN 6 Cylinder Commodore.
-The reduction of the
electrode gap by 0.1 mm (which lowers the spark plug required voltage)
Here is an explanation
of the spark plug heat range;