Idle sputter gets worse with A/C on - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum
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post #1 of 7 (permalink) Old 08-27-2013, 03:24 PM Thread Starter
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Idle sputter gets worse with A/C on

I have a headache this big (imagine a M6 sedan here) and it has a 5 pound sledgehammer written all over it!

2004 M6 V6 manual trans fusion swapped:

Has a slight but noticeable roughness in idle from cold startup. It sounds more like a "sputter" than a miss, although an occasional miss can be heard.

Turn on the air conditioner and the sputter gets noticeably worse.

The engine continues to run and does not die.

Increasing the throttle at idle smooths out the sputter

Further depressing the accelerator and the engine spools but a miss is heard.

When driven poor acceleration, "instant" and momentary surging and bucking present after about 25% throttle

WHAT HAS BEEN DONE:

New spark plugs installed

Ignition boots inspected

Before initial startup I removed and cleaned the throttle body, re-installed with new gasket

Air intake boot is OK

No vacuum leaks found

Exhaust is not restricted (thanks to 2 new cats)

Unfastened and lifted the top of the air cleaner box and manually restricted the air coming in to the air intake tube and the idle smooths out. If the air is restricted too much there is a "snap" noise at the throttle body and the idle picks up....appears to be the IAC functioning.

After startup the air mass sensor was cleaned, no help and exchanged with a known good air mass sensor, no help and runs identical to original air mass sensor.

When air mass meter is unplugged the engine idles butter-smooth, with or without air conditioner engaged but there is a constant idle surge from about 700 to 1100 RPM. Have not tried accelerating engine with air mass sensor unplugged as I don't think the engine will accelerate without it sending a signal.

This appears to be an idle air situation, perhaps a throttle position sensor amiss, but what I don't understand is why the idle smooths out when the air mass meter is unplugged.

Anyone have any ideas or have maybe run in to a similar problem?

Thanks everyone!
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post #2 of 7 (permalink) Old 08-27-2013, 10:55 PM Thread Starter
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Cool Update, problem found

So I called in a favor and asked a friend of mine to bring his Snap-On MODIS over (since mine is clapped out) and we mapped out the problems.

First the throttle position sensor signal was all over the place. Up, down, not stable in any way.

Second the number 4 and 5 ignition coils were weak and the number 6 coil was nearly inoperable.

I confirmed the diagnosis by installing the throttle body and three coils off my 2003 M6, base-resetting the ECU by disconnecting the negative battery cable and turning the ignition key on, then leaving the negative cable off for 10 minutes.

I just got back from driving the car nearly 50 miles and it runs like a scalded dog!

I swear to Christ, this car has been a needle-noodlin' son of a biatch....and I STILL have a headache! I've never had any car bend me over and bang me like a 16penny nail like this car has!
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post #3 of 7 (permalink) Old 08-28-2013, 01:22 PM
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Was gonna say EVERYTHING you brought to the table points to Poor Spark. Increasing the load on the engine (pulling away from a stop, turning on the AC, A lean Fuel mixture, charging a dead battery, all induce a greater load on the ignition system. From this, misfires occure. Boot alone seldom go bad so I'm glad you had extra coils.

The bad news is everyone wants to verify coils are GOOD or BAD by measuring the resistance. The problem is, unless the coil is burned up and NOT WORKING at all, they will always pass the resistance test. The failure mode is high voltage arc over. That is; its easier to spark through the coil body to +12V OR ECM logic to ground, than it is to deliver the charge to the plugs GAP. This is not a valid load test but doubling the plugs gap and confirming the coil can dry fire with Purple/White spark jumping a gap is about all we can do to verify it works. An orange or missed fire says throw the coil away.

Remember; lean AFR and adding load to the engine increase the demand on the ignition system. When the demand is such that its easier for that spark to jump internally than it is to the plugs gap we see all the things you did and reported up there.

Good Job and way to hang in there!

If you get bored, take a look here: 2nd post videos... http://forum.mazda6club.com/3-0l-v6/...ve-issues.html

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post #4 of 7 (permalink) Old 08-28-2013, 02:45 PM
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Yep, sounds like you have some dying coils.

Just putting it out there as a lot of people seem to have the same assumption, the boots on a coil are isolators. They are not the part that actually delivers the spark, and if the Coil itself is not producing enough power to burn properly.... no fresh isolator is going to solve that.

that is like having a dead brake pads, and replacing the hardware and keeping the old pads. You aren't actually accomplishing much.


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post #5 of 7 (permalink) Old 08-28-2013, 05:58 PM Thread Starter
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Well since yestirday aftirdnoon I have driven the car 125 miles using my throtle body and three of the ignition coils from my other M6 and I have a winner! No hesitation, no misses and no DTC's stored or pending!

I miss my Snap-On MODIS sooooo bad! I hope they get it fixed soon because trying to diagnose a problem without it is like driving the Autobahn while blindfolded!

I'll tell you what....Snap-On MODIS plus Alldata is an unbeatable combination fo' shizz!

I'm sure glad I've fostered such good relationships with the car community here in southwest Missouri!
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post #6 of 7 (permalink) Old 08-29-2013, 01:47 PM
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Really need to get me one of those....

though I have a pretty good success rate of diagnosing stuff on my own


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post #7 of 7 (permalink) Old 08-13-2019, 11:25 AM
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07 V6 Automatic here. I've got the same thing going on with mine now. OSIM6, you said you found out "the throttle position sensor signal was all over the place. Up, down, not stable in any way." Did swapping out the ignition coils make that go away?
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