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Spark plugs

8K views 19 replies 7 participants last post by  ricanrider69 
#1 ·
Hi, new here.
Please tell me which of the 4 plugs are primary.
I just this 96 1500 "D" for my girlfriend.
Thanks
 
#6 ·
only one plug fires on compression stroke, on the other side of motor at the same time a plug is firing on the exhuast stroke for better emissions, totally useless.
06 and other years of Dodge Ram hemi. Some are for smog and some not. Most Mercedes have 2 but the new ones can have 3 or 4 plugs and way too many valves.
Both plugs in the cylinder fire on every revolution, not every other, like in most 4-stroke engines.

The reason they fire on every revolution is for simplicity of the system, not for anything other than that. You just "waste" a spark on the exhaust cycle. Such a system is called a "wasted spark" system.

The reason you have two spark plugs is to create two flame fronts in the cylinder. This is slightly more efficient and allows you to have a different shaped combustion chamber which also adds to overall efficiency.

Personally, I think Honda used 2 plugs per cylinder on the first Shadow (in 1983) because most of the "big" bikes Honda was making at the time were 4 cylinders. A 4 cylinder bike has two coils, each with two spark plugs on it. That gives you 4 spark plugs, one for each cylinder. Instead of designing a new ignition system and coils for the new Shadow, I think they just used the existing ignition modules and coils, and put both spark plugs in the same cylinder. Just my opinion, not based on anything factual I have come across.
 
#10 ·
The Vulcan has a "wasted" spark in the USA.
The Vulcan has two coils and four plugs. How can this be if one coil is firing two plugs at he same time? :confused:
 
#15 ·
How it does that is the current leaves one side of the coil, travels down the plug wire, down the center electrode of the plug, jumps the gap to the ground electrode, through the cylinder head to the ground electrode of the other plug, jumps the gap to the center electrode, up the plug to the ignition wire and over to the other end of the coil. The coil, wires and plugs form a loop.
In this system, there is no ground on the secondary side of the coil.
You can see Ford's thinking by putting the precious metal on the ground side of half of the plugs as the spark is jumping in the opposite direction on these plugs.
 
#17 ·
Ah! Well, there ya go, leaned something new today. I always thought the coils on these motorcycles fired both plugs simultaneously, not in a loop sequence. :surprise:

 
#19 ·
both coils fire every time.
compression and exhaust. every time each piston approaches top dead centre, every thing fires.
makes for a very cheap ignition system and ecu.
The spark on the exhaust has no effect on engine performance, therefore its a wasted spark.
 
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