CherokeeXJoe

Hey guys, I just got a real quick question. So I got a mechanic to come give me a diagnostic on why I got no spark and my ignition coil was just hanging and wasn't bolted to the engine block as it should be and he said he's 100% that's the problem. So does the ignition coil need too be bolted to the engine block or was he just blowing smoke up my a** to get my money and run. Thanks

jordan96xj

The positive voltage that comes out of the ignition coil does eventually find ground through the engine block, but not via the bolts that hold it on. Ultimately, it jumps the gap of the spark plug and grounds via the engine block, which is of course grounded via a cable from the block back to the negative battery terminal. Coincidentally, this important block to battery path depends on bolts where the coil is fastened to the block. So perhaps he wasn't just looking at the coil, but noticed that those cables are not hooked up as they should be. Don't know.

However, an ignition coil that is swinging in the wind (not fastened) might experience a shorter service life due to banging around. I've heard that it is heat and vibration that really does them in. (however, one could argue that if heat and vibration is really so important, that being hard mounted to the block probably causes it to experience more constant vibration and heat than floating free). Though I don't care to test the theory.

CherokeeXJoe

thanks for the quick reply! So it doesn't finnd ground by being mounted on the block and doesn't need to be for the coil to start the jeep?

dzywicki

I don't think the coil itself is grounded. but, there are two large ground wires that connect to the mounting bolts for the coil. They are underneath the coil and go through the two bracket mounting holes. Regardless of the ground, your ignition coil should not be dangling. I have to imagine there are some other things wrong if you have the coil hanging loose.

Bugout4x4

Wut?

CherokeeXJoe

i don't see any wires below the coil, just the wire that goes in the coil and the one that goes out to the distributor. The coil was loose because I replaced it and just wanted to see if it would start. If not I would put the old one back in so i didn't bolt it up because I didn't think it needed to be. I guess I was right... unfortunately

jordan96xj

I just checked the FSM to try and be as accurate as possible. There are 2 grounds involved at the ignition coil. One that is driven by the PCM that is the driver for the ignition coil, and it would be coming in via the ignition coil connector. Then the other ground shown is a case ground, meaning the engine block. In the diagram it does not show the coil + voltage continuing on to the distributor and the plugs. But if it went directly from the coil to the engine block it would effectively be a short circuit, and no voltage would ever reach the distributor or the plugs.

So I'm going with my original answer. The ignition coil does not depend on its mounting bolts to provide ground for its functionality.

But the bolts it mounts to do serve as important connection points for grounding the engine block (which many things depend on). So if they were not connected back to battery negative, you could have a no-spark situation (because the block is not grounded).

jordan96xj

Did I get off base there?

RocketMouse

May not apply in our Jeeps...but what about an isolation mount? Those are used all the time in electronics. They don't have to necessarily provide a ground source, but just to isolate from swinging freely/and reduce exposure to excess vibrations.

CherokeeXJoe

Interesting, ive never heard that term... I think that's what the bolts are if they don't provide a ground. Would that affect the start up process? I assume not If it's only to reduce vibrations

RocketMouse

It's very common. Even inside every computer. If you open the case, you will see that the motherboards are mounted on Isolation stands and not mounted directly to the case itself. Rubberized or specific types of plastics used in electronics are most common.

Bugout4x4

No... you were absolutely right on the money. But I had to fire up my Engineer to Layman translation app to actually understand it. lol

Bugout4x4

Ford moved them off the engine and over to the fender well for awhile on their inline fours.

Bugout4x4

Jordan explained it here. Sometimes there are also ground wires for other systems that do need to be grounded against the block that the coil bracket bolts hold even though the coil it's self does not need to be grounded. That is just a bracket to hold the coil that bolts on there and doesn't need to be grounded, but if there are any ground wires and connectors right there, then those do need to be bolted up even if you don't bolt the coil bracket on.

dzywicki

Here is a picture of what it should look like. The coil is mounted to a bracket and the bracket is mounted to the block. The ground connectors are connected to the bolts that hold the bracket to the block. Those ground wires must be attached to the block somewhere.