We have struggled with a full throttle high rpm rev cut for the past 3 months on our Primera P11 GT with the SR20VE motor. It was almost as if the car had developed a soft rev limiter at 6500 rpm.
After testing the effect of powering more electrical parts (such as lights,stereo,camera etc etc) at high rpm we diagnosed the problem was down to insufficient electrical power.
We swapped out the plugs, changed the plug wires, closed the gap on the plugs, change the coil, changed the battery.
These changes had absolutely no effect.
We wired the alternator directly to the battery and no change.
We changed the afr and ignition timing and the only thing this proved was that the engine was extremely sensitive to ignition timing and fuel mixture.
The car would rev to the red line on part throttle but as soon as the throttle was pinned at high rpm, nothing, completely dead.
We noticed the battery was a bit low when we changed it out but running the battery in another car showed no issues.
The Solution To The Ignition Cut
Finally we disconnected the alternator from the charging system completely. Something was obviously sucking electricity out of the electrical system at high rpm, maybe it was the alternator.
And it turns out it was. Disconnecting the alternator and the car ran normally, albeit slightly richer.
The main thing is that the car would run cleanly to the red line with the alternator disconnected.
This points the finger 100% towards there being a faulty diode/s in the alternator.
If you ever have a soft rev limit on your car that for all the world feels like a bad coil but changing the ignition coil changes nothing, try disconnecting the alternator. I think it is the only thing that could drain so much power at high rpm to knock your spark out.
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