Engine shake

[DingoNatas]

Back again with yet another question that's probably been answered. 1997 Explorer E.B. V8 AWD has obtained a noticeable engine shake to it. I noticed it a few weeks ago while working on installing a new stereo. I had it idling and everything was running smooth then all of sudden it started “running rough”. I did some reading here on the forum for possible causes:

Misfire- There is no check engine light on.
Motor mounts- I've tried to shake the engine and it seems solid.
Timing Chain or resonance thingy- not a clue.

That's what I've done so far. I know not much but I've been working on the Transfer Case Rebuild for my other rig. I'm at work now but tomorrow after installing the other rigs transfer case I'm gonna tackle this new issue.

Any recommendations on where to start? I thought I'd start buy pulling the connectors from the plugs to the “distributor” on the “distributor” one by one to see if I can potentially find the plug that's potentially missing. Thoughts?

Oh and I thought I read somewhere about "vacuum" being an issue with an engine running rough, and to check the vacuum tubes for leaks/cracks. Any info on this? As in where do I look for and how do I look for potential issues here?

Thank you.

 

[1998Exp]

Is this 'roughness' only at idle, or also under load? If only at idle, I doubt that ignition is the issue. It could be the IAC (idle air control valve, located next to the throttle body - they are the first suspect for poor idling).
Also, note that this engine uses the 'waste spark' system, with each coil serving two cylinders, and the cylinder on the exhaust stroke 'firing' at the same time to complete the circuit. If you pull a plug wire you will be disrupting two cylinders at a time, not just one.

Back again with yet another question that's probably been answered. 1997 Explorer E.B. V8 AWD has obtained a noticeable engine shake to it. I noticed it a few weeks ago while working on installing a new stereo. I had it idling and everything was running smooth then all of sudden it started “running rough”. I did some reading here on the forum for possible causes:
...
Any recommendations on where to start? I thought I'd start buy pulling the connectors from the plugs to the “distributor” on the “distributor” one by one to see if I can potentially find the plug that's potentially missing. Thoughts?


Thank you.

 

[DingoNatas]

Thank you for the response. I noticed first at idle but after taking it for a spin today... all I can say is it feels.. different.. rougher. Don't get me wrong it will still get up and go. There's this noticeable extra sound and feeling in the rig. I know it's a bad explanation and very vague but it's the best I got. As far as testing the spark, will my test procedure work? Is there a potential of damaging something?

 

[DingoNatas]

Is this 'roughness' only at idle, or also under load? If only at idle, I doubt that ignition is the issue. It could be the IAC (idle air control valve, located next to the throttle body - they are the first suspect for poor idling).
Also, note that this engine uses the 'waste spark' system, with each coil serving two cylinders, and the cylinder on the exhaust stroke 'firing' at the same time to complete the circuit. If you pull a plug wire you will be disrupting two cylinders at a time, not just one.

With the waste spark, if I'm already getting a bad ignition in a cylinder my test would only prove my hypothesis, Correct?