Engine lugging at ~4700rpm

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Engine lugging at ~4700rpm

Postby DavidM046 » Fri Aug 17, 2018 10:43 am

Hey all,

My engine has started lugging as I go past about 4700 rpm. Once past, it seems to stop but it's not like I stay past 5000 rpm for long so I'm not sure. It doesn't matter what gear and it seems more pronounced the closer to WOT I am. When it starts lugging, the engine light starts flashing but when the RPM's drop back down, the light goes off.

It's a stock engine and the only thing that could be considered a mods to it is I installed a GWR Complete Street Exhaust combo with Hemholtz (ceramic headers, midpipe and muffler) a few months back.

I seem to remember reading that I didn't have to get a tune after the new exhaust install but I can't find that article again.

I always run Chevron Premium.

I do track it, but my track days are on hold until I get this taken care of.

Thoughts? Things to look at?

Many thanks!
David
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Re: Engine lugging at ~4700rpm

Postby DavidM046 » Fri Aug 17, 2018 2:54 pm

Checked to see if the CEL actually threw a code and it did. It said "#4 cylinder misfire". Which just leads to more questions. Thoughts on what could cause a misfire at high RPM but not at low RPM?
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Re: Engine lugging at ~4700rpm

Postby Brian » Fri Aug 17, 2018 4:48 pm

Sounds like a ignition coil failure, common on NA/NB and NC. Miatas are hard on ignition, my supercharged NC gets the coils changed at least once per year because in race use I toast them, we are trying some Corvette coils in the car to hopefully get more life out of them.

So, for you new ignition coils and fresh NGK plugs is my starting suggestion. And you don't want to put miles on the car chasing parts for this issue because it is likely dumping gas down the pipes and that will burn out the catalytic converter fast. Thus it is very common customers come in here for ignition coil failure AND catalyst efficiency code at same time because they melted the cats after the ignition coils started to fail. Eventually if you keep driving it the cats melt so much the exhaust is blocked and motor stalls with you stuck on the side of the road.
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Re: Engine lugging at ~4700rpm

Postby DavidM046 » Fri Aug 17, 2018 8:12 pm

Hey Brian, sounds good. I'll run down the new coils and NGKs path and happily, I have another vehicle so the Miata will stay in the garage until this is all sorted out.

No Cat codes yet so hopefully I caught this before any damage was done to anything else.

Thanks again,
David
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Re: Engine lugging at ~4700rpm

Postby DanielS172 » Sat Aug 18, 2018 12:36 pm

Before you spend money on new ignition coils, check to make sure the connection to the ignition coil is good. I had your exact same problem and everyone I talked to assured me it was the ignition coil. After spending ~$80 on a new one that didn't fix the problem, I learned that NCs (mainly the earlier ones) have poor connections to the ignition coils that will cause misfires and generally replicate the symptoms of bad coils. As a track-side fix I just zip-tied the coil harness and anchored it down so it couldn't move, which allowed me to finish my track weekend, thankfully. When I got home I purchased new coil pigtail connectors (like ~$30 on Amazon for 4 of them) for a permanent fix.
2006 with NC3 front end | OEM hardtop | full header/exhaust | FM stage II suspension and Wilwood LBBK | Blackbird Fabworx GT3 roll bar | TRMotorsports FF10s.
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Re: Engine lugging at ~4700rpm

Postby Brian » Sat Aug 18, 2018 4:27 pm

True, Mazda's gram strategy went too far with the super light wires to the coils. In my racing 2007 we have replaced the harness to the coils....twice. So, it might be coils/plugs and it could be wires to the coils. With the car running move the harness to the coils around and if the car sputters that's the wires. The fact the car lugging at upper rpms suggests in this case still coils rather than busted wire but there is still some chance it is the harness to coils vibrating enough to break connection only above 4700.
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