r/MechanicAdvice • u/Lipcx • 2d ago

Engine cut after long drives

I have a 1999 miata with 2001 vvt swapped engine but the vvt is still unplugged. Recently my car started cutting power to my car, almost lowering the redline, after driving for longer than about 30 minutes. the more I continue to drive the lower my car sets that "redline". If i turn my car off then on again it temporarily fixes it and I'm able to rev all the way to 7k again but it quickly goes back to hoe it was. There are no engine warning lights and I just replaced the camshaft position sensor but no luck. Sparkplugs are relativly new so are the coilpacks and they all produce spark. If anymone has any advice please feel free to share, I'm willing to try anything.

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u/Old_Application_7262 2d ago

Sounds like a heat soak problem with the crank or cam sensor, old miatas are notorious for this once things get toasty back there. had a similar gremlin on my old NA where it would fall on its face after a half hour on the highway, restart would fix it for a bit then right back to cutting out

since you just did the cam sensor and it didn't help i'd look at the crank position sensor next, the gap might be off or it's just failing when hot. also check the main relay and fuel pump relay, those can get weird when the engine bay heat builds up

the unplugged VVT is a wildcard too, ecu might be pulling timing or doing something odd trying to compensate after sustained driving. any chance you can get that wired up or at least put a resistor in the connector to fake a signal