Help with rough idle and acceleration - TIA

I can't speak on the picture you posted, but what is used on the current 4.0L is ONE coil firing TWO plugs simultaneously in OPPOSITE polarity.

If one coil doesn't work, 2 plugs don't get spark.

I knew that. Just wanted to be clear for those others who like to argue. :-)

We are not talking about a "regular" coil.

For What it's Worth

WJ Ignition System Description and Operation pages D2 & D3

IGNITION COIL?4.0L ENGINE

DESCRIPTION

A one-piece coil rail assembly containing three

individual coils is used on the 4.0L 6?cylinder engine

(Fig. 1). The coil rail must be replaced as one assembly.

The bottom of the coil is equipped with 6 individual

rubber boots (Fig. 1) to seal the 6 spark plugs to

the coil. Inside each rubber boot is a spring. The

spring is used for a mechanical contact between the

coil and the top of the spark plug. These rubber boots

and springs are a permanent part of the coil and are

not serviced separately.

(1) The coil is bolted directly to the cylinder head

(Fig. 2). One electrical connector (located at rear of

coil) is used for all three coils.

OPERATION

Although cylinder firing order is the same as 4.0L

Jeep engines of previous years, spark plug firing is

not. The 3 coils dual-fire the spark plugs on cylinders

1?6, 2?5 and/or 3?4. When one cylinder is being fired

(on compression stroke), the spark to the opposite

cylinder is being wasted (on exhaust stroke).

Battery voltage is supplied to the three ignition

coils from the ASD relay. The Powertrain Control

Module (PCM) opens and closes the ignition coil

ground circuit for ignition coil operation.

Base ignition timing is not adjustable. By controlling

the coil ground circuit, the PCM is able to set

the base timing and adjust the ignition timing

advance. This is done to meet changing engine operating

conditions.

The ignition coil is not oil filled. The windings are

embedded in an epoxy compound. This provides heat

and vibration resistance that allows the ignition coil

to be mounted on the engine.

Because of coil design, spark plug cables (secondary

cables) are not used. The cables are integral

within the coil rail.

One coil. Two spark plugs. Both spark plugs fire EVERY crankshaft revolution simultaneously. One spark plug always fires negatively (from center electrode to ground electrode). The other spark plug always fires positively (from ground electrode to center electrode).

Does that sound "parallel" to you?

You always have a link for everything, yet I haven't seen any links from you on this subject yet. Having trouble finding one that agrees with you?

I can't believe the BS Bill tries to palm off. You are right bllsht, two spark plugs share one coil in later distributorless 4.0L engines and both plugs are sent the spark voltage simultaneously. The spark plug immersed in the air-fuel mixture during the compression stroke will of course fire more readily than the other plug sitting in a cloud of post-ignition exaust gasses.

Jerry

bllsht wrote:

Right Jerry, almost. :-)

The cylinder on compression stroke has a higher voltage demand since it has to overcome cylinder pressure and the hydrocarbons. This is easily seen using an oscilloscope.

You finally got it! That's exactly how it works.

Hook your oscilloscope up to the positively fired cylinder and you will see an inverted pattern.

To the other post on the coil.

Obviously. That has squat all to do qith the current path I describe. The coil secondary HAS NO GROUND - being effectively a transformer, that's allowed. Current will flow from one end of the secondary, through one plug to ground, from ground through the second plug then back to the other end of the secondary coil. Simple isolation transformer secondary winding case - done all the time. All that's slightly unusual here is that part of the secondary circuit is accross

2 spark gaps.

OK you sold me. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com