Gen 3 2007 Jimny struggles when at around 75-80mph

I am not surprised it’s struggling at that speed, you are not far away from maximum speed. My Gen3 felt best around 50-55mph, my Gen4 slightly higher at 55-60mph, above that wind resistance starts going up.

I doubt I have ever been over 70 in a Jimny.

The only two times I have had meaningful issues with windage were once in a cross wind on the A1 near Coldstream that was unpleasant and then again I decided in October last year that being on top of mountains on the west coast in 90mph storm conditions was probably not worth the risk but otherwise it just uses more fuel to maintain progress.

jackonlyjack wrote:

You are thinking crank sensor 
But at this speed it could be other things 
Coil pack, fuel starvation, partial blocked cat/rear silencer 
Not many people push em past 70mph


 

I agree with this.  It is not so much the speed per se, as the fact that to push a Jimny that fast you are not only running at higher rpm but also at a higher loading (to counteract aero) and for a longer time.  In other words, you are really putting a lot of power (aka heat aka fuel) through the motor to maintain that speed.

I could definitely see a coil pack overheating, maybe plugs or wires too.  And your intake and exhaust paths should be pristine, to handle that kind of sustained flow. 



Of course nobody wants to hear it, but the Jimny is wildly unsafe at those speeds.  High unsprung weight, high CG with narrow & short wheelbase, and lousy brakes.  There are better ways to prove how tough you are.  But if you want to persist in using the wrong tool for the job, there is some diagnostic work to be done.