Spark plug reading

[Shawn]

I pulled these out of my Mazdaspeed 3 with 26k miles. I've been getting really bad gas mileage and the car has been running rich. I pulled out the plugs and replaced them and it seems like my gas mileage is better so far but only time will tell.

Can someone here take a look at the plugs and tell me whether they look bad or not?

 

[exdeath]

Need to show from end on. Heat range looks spot on (color banding/change in the middle of the ground strap) and yes it's rich (fine black soot) and burning a tiny bit of oil (white ash on the insulator, normal in any car due to PCV, etc).

The black soot/carbon = rich. A good mixture will give a dry orange tannish tint and won't appear so black and dark.

 

[Shawn]

Hmm, so the plugs are still good then? I'm not sure why I'm seeing better gas mileage with the new plugs, but it could just be a fluke. I didn't gap the new plugs though, so they are probably gapped for the NA mazda 3s.

Here is another pic:

 

[exdeath]

Your old ones are a bit carbon contaminated from the rich mixture. This leads to both poor spark due to carbon tracking and shorting to ground, and predetonation due to hot spots that could result in increased fuel trim and retarded timing.

It's not unusual for factory turbo cars to be excessively rich, but it might be worth checking out and at least making sure long term fuel trims are 1.0 (eg: zero fuel dynamically added to or subtracted from the precalibrated lookup table hard values) and not trending rich for some unknown reason.

Ideal mixure reading on a spark plug is a orange/tan/carmel color on the insulator and bottom half of the ground tab with a brown/honey to grey look on the threaded base ring.

 

[punjabiplaya]

speed3 runs pig rich - AFRs dip into the 9s under WOT without a tune. You should probably know this already (look at your exhaust tip(s) and the rear bumper and hatch). Mine is coated with soot flecks all the time. If you're got $600(new) or $450(used) to spare, pick up an AP.

AP will let you log/monitor LTFT and STFT (anything over 8% means something's wrong)
If you've got a gen1, dashhawk will let you monitor too.

Check out www.mazdaspeedforums.org

Got entire service manuals and guys who know a lot more stuff specific to the car - be warned, you will need thick skin.

 

[exdeath]

In a car like that you should be using copper plugs and changing them every 10k-20k anyway

 

[Shawn]

Why would copper be better than iridium?

 

[kornphlake]

Generally it's best to use whatever the OEM plugs are. If the factory plugs are iridium use them, if the factory plugs are copper use copper. The ignition system in my car fires the plug on the exhaust stroke:
http://en.wikipedia.org/wiki/Wasted_spark
The wasted spark supposedly has a tendency to foul platinum or iridium plugs faster than standard copper plugs. I have no idea what the recommended plug is for your vehicle, but you should find out and use the OEM plug.

 

[exdeath]

Why would copper be better than iridium?

Copper conducts heat out of the plug better and is available in colder heat ranges than platinum or iridium, desirable attributes in a forced induction application, especially if modded with higher boost, less fuel, and more timing.

The only drawback to copper is short lifespan of 10,000 to 20,000 miles and the only reason platinum and iridium plugs exist is for 100,000 mile OEM service intervals. If you are running a rich tune and having to replace plugs regularly anyway due to carbon fouling, might as well use copper.

 

[Eli]

I would say those look pretty good overall. Looks like you drive your car pretty hard.

I wonder what the white deposits on the center electrode ceramic are? That's the only thing that seems strange to me.

 

[Howard]

Copper conducts heat out of the plug better and is available in colder heat ranges than platinum or iridium, desirable attributes in a forced induction application, especially if modded with higher boost, less fuel, and more timing.

The only drawback to copper is short lifespan of 10,000 to 20,000 miles and the only reason platinum and iridium plugs exist is for 100,000 mile OEM service intervals. If you are running a rich tune and having to replace plugs regularly anyway due to carbon fouling, might as well use copper.

Aren't all spark plug conductors copper, with different platings? A pure iridium spark plug might just be a tad expensive.

EDIT: Interesting. Maybe they are pure.

 

[ayabe]

I thought this was a known thing with the speed3's, something to do with DI I thought.

 

[exdeath]

I thought this was a known thing with the speed3's, something to do with DI I thought.

That's the intake valves not being washed by the fuel in the intake ports. The spark plugs weren't in the path of the injected fuel either way, nor would you want it to be.

 

[Eli]

Aren't all spark plug conductors copper, with different platings? A pure iridium spark plug might just be a tad expensive.

EDIT: Interesting. Maybe they are pure.

No, I think you're correct. I don't think they're pure.

The iridium is just the tip and a small round patch on the ground electrode, AFAIK.

 

[Shawn]

I pulled the new plugs back out to check the gap and they were at .055"! I knew that guy at autozone didn't know what he was talking about. I ended up gaping them at .038". I was afraid to gap them any narrower because I had to bend them a lot to even get to .038 and I've heard that you shouldn't change that gap that dramatically because the plugs will wear quicker since it's no longer parallel with the conductor.

I guess I'll just change these out in about 10k miles or so and replace them with copper ones.

 

[SJP0tato]

Stick with the stock manufacturer (Denso ITV20). There's a lot of past discussion on the Mazdaspeed boards, and a reason why the copper plugs are a bad idea (Unfortunately I can't remember what it was, but stick with the stock metal type: Iridium).

RockAuto had the best price I could find on them a few months back:
http://www.rockauto.com/
Click on the "Part Number Search" tab, put in ITV20, choose Denso for the manufacturer.

Using the Denso plugs will allow proper gap while leaving the ground strap parallel to the electrode. Most of the other manufacturers have the issue you're describing where the ground strap winds up much closer on the outer edge than the inner to the electrode when gapped to factory spec, which is less than ideal.


As to the original problem, how bad MPG are you getting currently?

 

[Shawn]

13mpg with AC on, 15-16mpg with it off.

I'm light on the gas most of the time too. Hardly ever get it past 4000rpm. Usually shift at around 3000rpm.

 

[SJP0tato]

13mpg with AC on, 15-16mpg with it off.

I'm light on the gas most of the time too. Hardly ever get it past 4000rpm. Usually shift at around 3000rpm.

Sounds like something's definitely off then. Any check-engine light? What year is your car?

 

[punjabiplaya]

13mpg with AC on, 15-16mpg with it off.

I'm light on the gas most of the time too. Hardly ever get it past 4000rpm. Usually shift at around 3000rpm.

that's terrible. I get 27-28 mpg. Did you check O2 sensors? pcv valve? MAF might be dirty. I've got 28k+ on mine. try resetting ECU to see if your trims are screwed up.

 

[Shawn]

It is a 2008. I used to get a CEL light and dealership replaced O2 sensors (or so they claim). CEL hasn't come back since, but still getting terrible gas mileage.

 

[SJP0tato]

It is a 2008. I used to get a CEL light and dealership replaced O2 sensors (or so they claim). CEL hasn't come back since, but still getting terrible gas mileage.

How long ago was the service performed? If within the last few months I'd pay a trip back and let them know. You're still well within warranty, and they've already performed one service because of a previous problem.

 

[punjabiplaya]

something is def wrong

 

[Shawn]

How long ago was the service performed? If within the last few months I'd pay a trip back and let them know. You're still well within warranty, and they've already performed one service because of a previous problem.

It was about a year ago. Car is out of warranty now. It was manufactured 10/07.

 

[Shawn]

Forgot to mention that when I took the spark plugs out to adjust the gap they looked just as black around the rim as the ones I took out and I've only driven about 100 miles since I put them in.

 

[exdeath]

Your shit is richer than Bill Gates. Get it fixed ASAP then change your oil.