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post #1 of 4 (permalink) Old 08-18-2016, 06:00 PM Thread Starter
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Engine Running Rough

Ok so obviously with an old car there is many things that can go wrong and without actually seeing the vehicle or being there to diagnose it it's almost impossible to say whats wrong. That's a given so with that behind us what's the most likely problem?

Year: 2004
Make: Mazda
Model: 6S (3.0L, V6)

Recently the catalytic converter has gone in bank 2(P0400, P0401).
I have replaced all the spark plugs and coil packs(all new)
4 wires in the fusebox have been rewired (spliced together and heat shrink over to waterproof, this did contain the largest wire gauge in the boxes white connector and the ground wire.)
In the past IPC, ABS, and TCM could light up all together when the weather was humid and the car would run like sh*t.
PCV Valve was just changed < 5 mi (10 kilometers)
Engine and transmission oil/filter were changed today (0k)
Both Tensioners and drive belts (Water pump and ac) replaced <10K
Brake pads and rotors were upgraded to performance parts.

Vehicle is STILL running roughly. After codes for Cylinder 5, 6, and 3 misfire came up, Replaced all the spark plugs and coil packs as well as the intake manifold gasket. Cylinder 5 and 6 no error codes after. After about 2 to 3 weeks cylinder 3 had another misfire and ran like sh*t again. The more humid, the worse it runs. A tech said it could be a possible vac leak (if so, how could I test this to confirm or deny?) tested vehicle in drive and elevating rpm to about 1500 while brake applied. This is when cylinder 3 appeared to fail and all spark plugs and coil packs were replaced.

Bank 2 Cat is done (temp below threshold)

Wire was found near the rad (loose and unconnected). It was in a somewhat triangular form and was a rubber orange piece. (see pic1 and 2) Is this supposed to be connected anywhere? There did not appear to be any connecting pins inside the piece. Where a pin should have been appeared to be sealed rubber. Zip tied it out of the way so as to not get caught in rad fan.

Lastly there is a ticking sound while the engine is running. Louder or more noticeable in drive as it's almost constant, however in neutral or park it's only slightly noticeable with slightly elevated rpm (near 1500 instead of idle). Have heard it here and there at highway speeds but very subtle. One tech said possible rad fan, however with the cat gone on bank 2 could it possibly be that?
- I am aware that the cat being gone and possibly plugged can damage the engine and am working on getting a new cat.


If any more info is needed or more specific details are needed, please don't hesitate to ask. I'm glad to take more pictures or videos if needed or provide more info. I am completly open to all ideas even ones I've tried. Even if it sounds stupid, it could be something, weirder things have happened.
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Last edited by TheNexusElement; 08-18-2016 at 06:54 PM.
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post #2 of 4 (permalink) Old 08-18-2016, 08:55 PM
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I seem to be having the same issue as well. Drove it a few miles with no issues but , when stopped at a red light , the Tach jumps from 1000 to 700 , when in Neutral it seemed to level of at a smooth idle of 1000rpm , put it back into Drive it dips down to 900 than operates normally .

Mazda 6S

Changed the plugs, Oil change, New Radiator , Installed New PCV valve. Checked that there was NO leaks in all my hoses.

You mentioned your Mazda tech stated, Humidity affects the Engine performance , resulting in Misfire , and everything else that comes with a naughty Engine ! :-)

Todays drive to and from work proved good so far , but I can see many people have the same issues .

THE RED PLUG ...looks like a plug for supplemental fog lights . I cant seem to find anything it would plug into .

I will touch back with a report on how the engine is operating .
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post #3 of 4 (permalink) Old 10-02-2016, 12:53 AM
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Maybe a MAF sensor? That's about the only thing I can think of
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post #4 of 4 (permalink) Old 10-02-2016, 11:41 AM
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Rubber air intake hose is famous for cracking and causing most of these problems. If it is hard at all just replace it. Also, did you install new plenum gaskets when you did the plugs?

2004 Mazda 6s 3.0 5dr. 5spd never ending money vacuum project:
CP-E headers w/catted mid + Magnaflow carback/AEM CAI/3.7L TB/Speed6 springs/RX-8 wheels
AWR 70D Enginemount/CP-E Dogbone/Custom urethane stock trans mount
Ralco shortshifter/Bose w/Auxmod/sharkfin antenna/lots of little things...
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