Anyone know if the 4.0L ignition is Waste Spark design?

[michael loibl]

For those not familiar with the term, it is the type of ignition where each cylinder is paired with a second cylinder and they spark simultaneously, even though one of them is on an exhaust stoke at that moment.

So basically in that design Each cylinder will spark on every engine rotation, not just the every other rotation that is required in a four stroke motor.

Depending on the answer to this question, I will follow up with my reason for asking

 

[boominXplorer]

Yes it is

 

[michael loibl]

Ok thank you, I seem to be getting less than ideal spark out of # 2 and #3
There is a noticeable rough idle when in drive at a standstill, but no check engine light.
Early this morning on a hunch, I attached my old school timing light to each spark plug wire right at the coil. The other four wires produced a proper consistent strobe light, but number two and three seemed to fail to trigger the strobe about 25% of the time.
The wires in my attached photo marked in red and yellow are the two that are not functioning correctly. I was considering switching them with the Blue and green directly across from them temporarily to confirm that the problem follows before I order a replacement coil assembly. Thank you

 

[ashleyroachclip]

That is a good sign the coil is on it's way out

 

[shucker1]

The wires in my attached photo marked in red and yellow are the two that are not functioning correctly. I was considering switching them with the Blue and green directly across from them temporarily to confirm that the problem follows before I order a replacement coil assembly.

As long as you trade the whole wire assembly. Just swapping coil side ends will change your firing order.

But you already know that...

 

[michael loibl]

Just an update, I borrowed a coil assembly from Another 4.0L and swapped in last night. No difference in the rough idle on my truck. It seems to have normal power when driving so that eliminates a lot of things that could have failed in my mind.

I started checking vacuum hoses for leaks last nite, but they seem ok. I am going to pick up a can of throttlebody cleaner today if I get a chance and give that a try before I go any further.

No check engine lights, does anyone have any other thoughts and recommendations on what I should check next?

 

[boominXplorer]

new plugs and wires?

 

[Davidm53]

Run Seafoam or Techron for a few tanks.

 

[michael loibl]

I am kind of ruling out plugs and wires being it feels fine on the road, no loss of power. I even towed my 3,000 pound trailer with it a few days ago and It felt 100% on the road. Just a little shaky at Idle. I will try the seafoam for the next two tanks of fuel while I continue checking things. Thank you

 

[fastpakr]

Pull the plugs and look at them.

 

[shucker1]

new plugs and wires?

Like @boominXplorer said.

If I am not mistaken the ignition system is not only wasted spark but demand spark as well.

Light loads you don't need as much voltage so misfires show up. Heavy loads you have more spark so.. No misfire.

My 98 had the same symptoms. My wife drove it and she always said it was missing...

Thought she was nuts. I drove it I couldn't feel a thing.

Friend of mine was working for a dealer and the time.

He explained how the spark system worked.

Changed wires....

Problem gone..

P.S. NEVER told the wife she was right....

That's just pure suicide.