Mazdaspeed Miata Blog
I drove Kiryu to work a few days ago and had a really bad hesitation under boost, to the point where it bordered on dangerous. I got her home and had an immediate idea of what was causing it, I pulled the plugs and my suspicion was confirmed.
Someone that put in regular copper NGK plugs instead of the iridium plugs that the car calls for. The reason you can't run copper plugs in a turbocharged MSM is because they can't handle the higher heat range that a turbocharged engine produces, and they tend to foul out quickly under boost leading to wasted spark and massive hesitation issues and possibly detonation. Fortunately, the plugs show no signs of detonation or other issues.
Another issue with these plugs was the gap. MSM calls for 0.026" to 0.030", these coper plugs were at 0.046", gapped for a non-boosted Miata. One set of proper BKR7EIX-11 iridium plugs gapped to 0.028" later and the the car was running so much smoother with far less hesitation.
I could still detect a slight hesitation shifting from 2nd to 3rd gear, so I put the code scanner ont he car and discovered a P2009 code, and a P0446 code. The P2009 code indicates a problem with the intake manifold runner control system, which can cause hesitation and poor performance and leads back to this lovely VTCS solenoid.
The P0446 code indicates a problem with the evaporative emissions control system, which can also affect engine performance. I ordered the VTCS solenoid first and I'll clear the codes to see if that resolves the hesitation issue completely. If it doesn't, I'll be trying to source a EVAP vent solenoid as well to see if that clears up the P0446 code.
The car is due for it's OBD2 inspection and registration renewal in Febrauary, so I'm hoping to get these issues resolved asap. On another note, the car definitely needs some new tires soon, and I'm thinking of replacing the bent Advanti S1 Storm 15X9 wheels with something a little more stout when I change the tires out.
Ideally, I would love to have the car race ready at a moments notice for the LSR PCA autocross events this year as a fun distraction from my SCCA C-street events in the ND2.
After a long hiatus from autocrossing, I finally got Kiryu back out on the track today at the PCA Houston Region autocross event held at the Houston Police Academy. It had been nearly 3 years since I last took Kiryu out to an autocross event, and I have to say, it felt great to be back behind the wheel of my favorite Miata again. The car performed flawlessly throughout the day, and I was able to get some decent times in despite being a bit rusty. The new tires I put on last year really made a difference in grip and handling, and I was able to push the car harder than I thought I would be able to. Overall, it was a fantastic day of driving and I can't wait to get Kiryu back out on the track again soon.
Today I took some time to get acquainted with the lift services at the Shop Club Houston today to get the oil change service done on Kiryu. As a general rule, I usually change the oil in 1 year or 5,000 miles, whichever comes first. In this particular instance, we were well below on mileage but hitting that one year mark. What’s a little surprising is that the oil that came out was much, much, much darker than I remember it ever being on a 5K interval, so then I had to question myself on when I last actually changed it A quick look at my log book revealed I had changed it two years ago… Oops. 4 quarts of Mobil 1 5W30 Extended Performance oil and a new Mobile 1 oil filter and the old-girl was ready for the wash bay. I also took the time to clean the interior of the car, and I have to say, it looks pretty darn good for a 20-year-old car. The paint will need a good cleaning and polish sometime this year when it's time for a fresh coat of sealant, but the interior is still in great shape. I think I’ll be keeping this car for a long time to come.