missing under WOT
#1
Junior Member
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Join Date: Mar 2012
Location: Edmonton, Canada
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missing under WOT
My Spec Miata, 99, starts to miss at about 6500 rpm, in any gear, at WOT. Not all the time, but often enough.
It may be heat related, OK early in a run, then developing as the engine bay gets hotter, but it is not always that clear.
I replaced the coil pack with another used one, and it stopped for two weekends, But now it is back.
The engine is freshly rebuilt. The fuel filter was changed at the start of last season.
What are the other possible culprits, are there some well known ones?
It may be heat related, OK early in a run, then developing as the engine bay gets hotter, but it is not always that clear.
I replaced the coil pack with another used one, and it stopped for two weekends, But now it is back.
The engine is freshly rebuilt. The fuel filter was changed at the start of last season.
What are the other possible culprits, are there some well known ones?
#3
Retired Mech Design Engr
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Location: Seneca, SC
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I went to COP's just for insurance. I did not want to have to purchase a new, stock coil, when one went bad; and THEN go to COP's. Toyota COP's have plenty of spark for my power level.
You may consider the NGK Iridium spark plugs as well.
DNM
You may consider the NGK Iridium spark plugs as well.
DNM
#7
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SM rules are very strict, no real way to do much about the cooling in a 99.
I can look at the crank angle sensor wiring, the cam angle sensor wiring, and another coil pack. But it feels like throwing parts at the problem. However, there may be no choice but to take that approach.
I just thought it was worth asking about the main culprits, so I have an idea about which parts to throw at it, and don't miss some.
I can look at the crank angle sensor wiring, the cam angle sensor wiring, and another coil pack. But it feels like throwing parts at the problem. However, there may be no choice but to take that approach.
I just thought it was worth asking about the main culprits, so I have an idea about which parts to throw at it, and don't miss some.
#9
I think Ballenger Motorsport makes a cam sensor specifically for this purpose. i don't know 100% if this is your issue or not but if I were running a spec miata I would likely be running this too.
https://www.bmotorsports.com/shop/pr...oducts_id/4307
https://www.bmotorsports.com/shop/pr...oducts_id/4307
#13
Buy some cheap copper plugs and gap em on the tighter side of spec. They tend to run cooler that IR or Platinum plugs. You can also try dropping one heat range as well since fouling is less likely in your situation.
I know it sounds too simple but I would definitely start there.. Some well respected tuners over the years kept pointing me to copper on my big power builds. Misfires was something I always struggled with on IK22's and IK21's. Once I swapped to copper (Bosch or NGK) my problems were solved.
I know it sounds too simple but I would definitely start there.. Some well respected tuners over the years kept pointing me to copper on my big power builds. Misfires was something I always struggled with on IK22's and IK21's. Once I swapped to copper (Bosch or NGK) my problems were solved.
#14
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If allowed by the rules, replace your cam and crank angle connectors with DTM connectors (that's the meat of what Ballenger is selling). The OEM sensor are not meant for long term motorsport use. Make sure the cam angle sensor wires are strain relieved.
#17
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Location: Edmonton, Canada
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Well, thought I would complete the discussion.
Replaced coils, not so bad but still there.
Replaced cam angle sensor with the fancy pig-tailed version referenced above, improved, but once in a while a hiccup.
Replaced spark plugs, problem solved.
Sadly, then had to replace engine, due to thrust bearing failure.
Went with new coils and cam angle sensor, but used old dirty plugs during break in.
Once in a while a miss around 6500.
Replaced plugs, seems to be gone.
At least the new engine pulls nicely.
Replaced coils, not so bad but still there.
Replaced cam angle sensor with the fancy pig-tailed version referenced above, improved, but once in a while a hiccup.
Replaced spark plugs, problem solved.
Sadly, then had to replace engine, due to thrust bearing failure.
Went with new coils and cam angle sensor, but used old dirty plugs during break in.
Once in a while a miss around 6500.
Replaced plugs, seems to be gone.
At least the new engine pulls nicely.
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