Strange deposit on sparks/Rough idle
 

Has anyone had any issues with a rough idle requiring spark plug replacement? If so, did the leading and trailing spark plugs have a strange brown deposit on the plugs?

I have brought my 8 in for rough idling 3 times and 1 flood. The car actually feels like a misfire and one of the times the whole car actually shaked. The first time I had the plugs replaced, one was cracked and black. The last time they noticed a strange brown deposit on only one half of both the leading and trailing plugs.

The deposit rubs off fairly easily, however my tech at the dealer who has worked on RX-7's and 8's for years has never seen this color. He said it could be something was introduced into the fuel mix like kerosene.

He contacted Mazda's engineers to look into it and after 3 days gave me back my car. He hasn't heard from Mazda yet, but I am worried that something may be wrong with the engine.

Assuming you haven't been adding anything to the fuel (octane booster, etc), the brown might be from high level of MTBE in the gas.

Hi there -

I too have been having mis-firing at idle in my car, and I am taking it to a dealer on Thursday to see what's going on with it. There is a replacement spark plug announcement for the plugs that might be useful for you, which I have linked here:

http://www.finishlineperformance.com...h_rf04-04.html

As for the brown deposits on your sparks, I don't really know, sorry. For more information try searching the site for "mis-fire" and "engine idles off". Also look in the Tech garage. Best of luck - H

Is your coolant level going down?

Can you ask the tech to elaborate on the optional hot plug? Im from NY (cold nights in the winter)... Do the cars come with this already? Will it make a big difference? Will it change the MPG?

There isn't much to elaborate about. A hotter plug will allow the electrode to burn deposits off more easily. Thing is though that when the engine is hot, it might not be able to radiate off enough heat to keep the electrode from expanding and cracking the ceramic insulator. I doubt if the hotter plug per se will increase mileage or performance or any such, but cleaner plugs will.

The Service Rep seemed pretty interested in throwing these plugs into my car, but I don't know. I worry about 100 degree summer days, and if I decide to flog the engine, however, I am going to do whatever they advise. They have a better chance of getting the car right than I do, so I guess that I'll find out. If anything interesting comes out of the experience, I'll post it.

FWIW, According to Mazda, the hotter plug is "... only for customers who often drive their car at very low speed which causes the plugs to foul easily"

Once you flood the car make sure to get new plugs because the flooded chamber fouls the plugs.

I got the new plugs with no other modifications to my engine. I had the L Flash installed two weeks before by another dealer which did not fix my unstable idle problem.

The New plugs completely fixed my idle problem. I am getting better mileage than I ever have before, now 21 MPG in mixed heavy highway driving, more power, more responsive throttle as well as more responsive revs going both up and down the tach. All in all, this was the fix that I was looking for. The car runs GREAT, the way that I always thought that it should when I bought it and that it never did even on the first day that I owned it. Fouled plugs were definitely a problem for me, and I do drive alot at low speeds in stop and go traffic. That's the beauty of living in a crowded North Eastern city. Love my 8!

I think I am going to make the switch as well, because I have to hold the ignition when Im starting up for way to long....

Nubo/Haze,

Thanks for the post responses. I have been out of town a few weeks and have not been driving my 8. Now that I am back and driving the car I noticed a smoother idle, more mid range power and quicker acceleration. The gas mileage has improved yet I wont know by how much until tomorrow when I fill up.

I will have to check with the dealer to see what type of plugs he replaced. I do get caught in traffic and drive stop and go as well as cold weather. Again this is my third set of plugs and I understand these are not cheap ($280).

I have yet to hear from Mazda about the cause of the fouled plugs. I think this is an issue. I will follow up with them again.

Third set of plugs in how many miles?

That's alot of plugs, and I have heard that they are quite expensive. If it happens again or your dealer finds some root cause problem, please post it. My car is still running fine with the new plugs after a couple of thousand miles, but I would be interested in your experience down the road. Thanks alot - Haze

Hah! My plugs must look brand new then. ;)

Dropping a heat range is a good idea for the drivers of RX-8s who experience stop start, low speed traffic each day.

Mazda quoted BUR-6EQ-L + BUR9EQ-T for the 20B powered JC Cosmo (auto) due to the lower revving.

Changed to hotter plugs on several Rx-8 for people recently. They simply would not have gotten 5000km out of a set of 7+9's. Fitted a set of BUR6EQ + BUR8EQ as recomended by Mazda & many other rotary shops.

Now without the dreaded carbon build up so typical with plugs too cold for your driving style. They should get 5000km easy..........:)

Anyone notice benefits from an inter-city highway trip? After months of only commuting, put on about 650 I-95 miles over the weekend and now car seems all-around more responsive and happier. Could there be some carbon burn-off? (Or just noticing absence of wife, luggage, etc.?)