'94 3.0L engine vibration/shudder

[MA Ranger]

My '94 XLT (3.0, 2WD, automatic) has suddenly developed a severe shudder/vibration that appears to be coming from the engine (it varies with pressure applied to the gas pedal and is the same with the transmission in drive, park or reverse so I don't think it's in the drive train or transmission. U-joints were all replaced about two years ago.). Other symptoms: exhaust louder than normal, decrease in gas mileage and less power. It was running normal a few days ago. I parked it for about 10 minutes after driving at highway speeds for about 100 miles. When I started it up and backed out of the parking spot, the engine was shuddering and vibrating when I stepped on the gas and the exhaust was noticeably louder. At lower speeds and when the engine is under a load (accelerating from a standing stop or going up a hill), it almost sounds like a motorcycle. The vibration smoothes out a little bit at driving speeds around town (40 - 45 mph) but it's definitely still there.

What I've done so far:

Put a bottle of Gumout Regain fuel system cleaner in the gas tank (I normally put fuel injector or system cleaner in it about twice a month and I cleaned both the lower and upper intakes when I took them off the engine about six months ago)

Scanned the engine - Key on Engine off (KOEO) test. Both hard and continuous codes showed "111" system pass (the "check engine light" isn't on)

Did a simple check on the EGR valve - temporarily blocked the port to the upper intake with sheet metal - no change in any of the symptoms (I did this to check if the EGR valve was stuck in the open position).

Is it possible for the Powertrain Control Module to be bad, but still be able to pass a KOEO test?

Any help would be appreciated. Thank you

 

[basketranger]

have u done a compression check? (WET OR DRY)

 

[MA Ranger]

No, not yet. Thanks

 

[helpme]

Mine has done that before...

but cleared up on its own before I could run it down. It does it about once every two years or so and only lasts for 5 to 10 secs.
I figured it was just bad gas or maybe water in the gas.
I'd check your plug wires first. When was the last time they were changed? My experience is the plug wires won't last as long as the plugs. Make sure the plug wires have not melted and arcing from being in contact with the exhaust manifold.
Make sure all the plug wires are on firmly (when the engine is off and cold).
If you change plug wires, change only one at a time.
As for plugs, I think they last forever unless you've got a fouling condition.
Clean/ check the contacts on your distributor and rotor.
I don't think its going to be a computer problem.
I've got 206K miles on mine.
Good luck.

 

[MA Ranger]

Helpme,

Thank you for your help. It was the plug wires. All set now - good to go!