Don Hammond

Being new to the forum and viewing the wealth of information from the participants, I thought I might be able to get some feedback on the following question which came up again in a discussion with my cousin who races rotary powered mini-stocks:
I purchase an '88 TII new and noticed the trailing plugs were not firing after @ 3,000 miles. Changed plugs and once again the plugs stopped firing after only a few days. Long story short, Mazda Zone Tech got involved and during one of the tests, I disconnected the leading igniter & engine died. Re-connected same and while the engine was running, disconnected a tailing wire and grounded same and had spark from the wire, but plugs would not fire. I also had very high exhuast temps which would heat the fuel in the tank to 150/160 degrees and caused a herrendous fuel odor on warm days. He agreed, Mazda was aware of the problems, so they took the '88 back & I received an '89 in May of '89, which I still own, with no problems even with performance upgrades!
Sorry for the length of this, but just curious if any ones knows why..

RETed

Bad trailing coils/ignitors?



-Ted

Don Hammond

Thanks for the reply, but when the trailing plug wires were removed from the plugs and put to ground, there was a spark @ 1/2" to 3/4" long. If new plugs were installed, they would fire, but for only a short time.

BBW

Just curious. When the "new" plugs stoped firing, how did they look?

Don Hammond

BBW-You wouldn't be able to tell they weren't firing by looking at them. They had a very similar look as the leading plugs, in fact that was one item the Mazda tech mentioned. The way I monitered the plugs was with a "normal" timing light, which wouldn't light. If you use a Snap-On, or the like, it will pick up minimum voltage and light, even though the plugs aren't firing.

BBW

Don Hammond,
I am sorry. What I meant to ask was the wear pattern/deposite residuals on the trailing plugs after taking them out of engine when they had stopped firing.
Maybe you can try the Car Talk radio show that comes on on Saturday. Their address is www.cartalk.com. Move the pointer to "Our Lousy Radio Show" to locate station directory. Those two MIT guys are pretty good at figuring out strange car problems.

As far as the high exhaust temperature is concerned, maybe it is a result of the catalytic converter that is trying to burn off the higher level of hydro-carbon.

turboren

Did you try replacing the trailing coils and ignitors with known good ones? Just because you are getting spark with plugs grounded to the body doesn't necessarily mean you are getting spark in the combustion chambers. It takes a lot more energy to jump a gap under the pressures found in the combustion chambers (85 psi+, or over 5x atmospheric pressure), than in atmospheric pressure.

Is the spark bright and blue, or weak and yellow. GM's with HEI tend to have their ignition control modules go out, which causes the spark to still jump the gap in atmospehic pressure, but it's yellow. The equivalent for our cars would be the igniter.

Ren