As a automotive tech, I rarely work on mazda's but he , the customer was insistant in having me troubleshoot a run rough/low power issue after he changed the spark plugs.

What he did was change the front three spark plugs. He removed the coil packs, replaced the plugs and reinstalled. The engine has the well known 1 cylinder thump miss characteristic of vacuum leak,bad spark misfire or just plain dead cylinder from no compression.

So I attempt to isolate the issue. I checked the plugs, re tightened and same issue. I pulled all three coil packs and checked the primary and secondary resistance. Primary side of coils 4,5,6 were less then one ohm each. Secondary side was 19k ohms on all three coils so all are good.

I would pull the coil on #5 coil pack. http://autorepair.about.com/library/...bl-fo-1733.htm
Had a very noticeable engine rpm drop so that cylinder was good. Pulled the coil pack connectors to #4 and #6 and got almost no change in cylinder rpm drop. I swapped 5 and 6 coil packs and noticed that #5 has little rpm change when disconnecting it.

Cylinder bank with plugs 4,5,6 is much hotter then the rear cylinder bank and getting the rotten egg smell out the tail pile "hydrogen sulfide
smell".

Now, the owner did overtorqe the intake manifold bolts pictured here with the white arrows. The nuts, or plastic that hold the nuts are broke. I suspect a a vacuum leak as a result of this. I put my propane bottle to these points over and under the manifold. Got little if any rpm change. I tried my starter fluid but the nozzle broke before I had any change to use it.

Catalytic converter is 500F at the front and 700F at the rear.

So, what could be the issue? I highly suspect a vacuum leak but it was not evident. All Spark coils on 4,5,6 Ohm readings are good. I inspected the spark on #6 coil with a tester and got sufficient spark.

Do modern day scanner read the Kvs or general health of these coils while in operation? How do I pull codes with the onboard computer?

I know the snapon modis is a very pricy scanner and have thought of the Launch 431 scanner that is so popular to technicans over seas at a big cost savings over the snapon.

Your thoughs much appriciated.

Thanks

 

Missfire v6 mazda,
hi there,was the engine running ok before he changed the plugs himself???, if yes is the answer ,what i once experienced was a small piece of spark plug porcelain insulator broke off as a result of incorrectly fitting socket being used to remove the old plugs,this dropped into the cylinder when plug was lifted ,and wedged under a valve,causing low compression,and missfire, have a good look at the old plugs just in case, their colour might give u another clue, its always difficult when working on an engine after someone else has had a go first.
Gareth

 

Is this a mazda tribute 2001 3.0 v6? Take a look at your wire loom on cylinders 4,5,6. Yours may be one of the few where wires 4 and 6 may looked crossed to coil packs 4 and 6. As a automotive tech, the way the wire loom is dressed is almost always the way the DIS plugs plug into the coil packs. I got the answer from another SAE tech.


Wire loom is miswired from factory. So while #4 DIS plug is next to #4 coild module, it belongs to #6. Same with #6 DIS plug should go to #4.

The loom basicly is miswired to impropper length from the factory. I have yet to confirm this on the customers car but he could not wait and drove it to a shop. Other shop is now doing unessesary work to trace down this issue.

His symptoms are unusally hot exaust in the 456 cylinder banks and engine kickback when starting.

So if the wiring is backwards on #4 and #6 then #6 will fire on the intake stroke. The resulting ignition of the fuel, which starts to squirt when the piston is BTDC will push back on that piston causing kickback and force some of the burnt mixture back into the intake causing pulses in the intake system.

this will also hurt idle rpm.

#6 cylinder will fire on the exaust stroke and send unburnt fuel into the exaust bank. This is why it is so much hotter on the front bank then the rear bank. At the same time, the partially burnt mixture is sent to the catalytic converter where the cat tries to catalyze the mixture but cannot. It is overwhelmed. What mixture it cannot catalyze is sent out the tail pipe as hydrogen sulfide. This is the typical order of rotten eggs of a improperly running engine.

The o2 sensor will sence a much stronger presence of hydrocarbons and will signal the ECM to trim back on the fuel/air mixture nessesary for a normal idle and proper fuel mixture. This will make the engine run lean and thus, a idle that is hard to maintain.

 

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