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Hey guys, I have a question some of you may have an answer to. I have just bought a 93 LS V6 and there is a "pulsing" that is rpm dependant. You notice the vibration mostly in the 2-3k rpm and it doesn't matter at what speed. And it appears under acceleration only. Thought it might bea misfiring sparkplug but checked that while engine was running by unplugging each plug one at a time... couldn't locate a faulty plug. I seriously doubt it's anything with the drive train since this is rpm dependant. Could it be an injector problem or timing? You can even hear the pulsing in park (can't so much feel) by hand reving the engine. Also at a very specific rpm the engine will bog down and then return to normal rpm and then repeat the cyle over and over every 2-3 sec. Like there's a crack between the MAS and trottle body. Any suggestions or hints? Thanks...
 

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A few ideas for you:

Any time someone reports roughness or vibration on a KL03 V6, I always first suggest a new set of plug wires or at least ask how long it's been since they were replaced. The OEM units are pretty bad and weather poorly, age and crack allowing corona and HV leakage.

Remove the plug wires from the plugs and look into the plug wells for evidence of oil buildup from leaking valve cover gaskets. Oil in there can degrade the plug wires and cause misfiring. The plugs themselves, unless they're really old, are probably fine.

Check the condition of the distributor cap and rotor. Look for cracks, carbon tracking, evidence of burning or corrosion on the tip of the rotor and the contacts on the cap. Check the condition too of the cap sealing gasket and replace it if necessary. If there's evidence the distributor has been moved, check the spark timing.

Check the PCV valve to make sure it's free and not stuck open. Take it out and shake it...listen for the rattle.

Take the VAF off the car and the TB elbow too. Carefully move the center-cone of the VAF in and out, making sure its movement is smooth and doesn't bind anywhere. Check the VAF-TB elbow for cracking etc.

If none of these help (and I suspect the plug wires are the fault here), you'll have to dig deeper. Things like a compression test, 'scoping the ignition system and checking firing voltage and burn times, checking for injector leakage or clogging (i.e. removing the fuel rail and performing tests) etc. Check the easiest, most basic things first though.

Good luck,
 

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Well i had a prob on my first gen where i would give it gas and the motor would rev but i wouldnt accelerate, i finally figured out that everytime i gave it gas it would cut down to 2 cyinders, weirdest damnt thing ever. The problem ended up being the distributor, you might want to check out the cap rotor, module and what not.
 
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I have the same problem on my 95 MX-6 with 104,000 miles.

The engine feels very smooth at idle (sometimes I even have to check the tach to make sure its running) and it feels very smooth once the RPMS are above 3000 or so. But, when I'm attempting to drive the car "normal" which for me seems to fall in the 2k to 3k range for shifting, I notice a noise which I can describe in no other way other than a faint d-d-d-d-d-d-d noise and the car feel kinda sluggish. I've taken the car to my mechanic (local Mazda specialist) several times on this and they've said that there is nothing wrong. I also did the same thing as you, pulled each plug wire off looking for a miss. Couldn't find one... New wires, dist, rotor, NGK plugs, fuel and air filters were installed at the 90k service.

After doing some research on the net I suspected that it might be carbon knock, since the symptoms of CK are similar to what I am having. I put in 2 cans of Techron injector cleaner and over the weekend put about 500 highway miles on the car. It seems better (quieter) but I can still tell that something is happening that just doesn't sound right.

I'll keep you posted if I figure out anything. Good luck.
 
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