JFB Tech

I bought the last frequency limiter off the original manufacturer through Turbo Technics. Stupidly, I potted it into it's case before noting the component values and PCB layout. Wish I had now. If I remember correctly there were only a few components on the board. I do have all the details for the DCU which controlled the 5th injector as I made my own when the original fried itself. I also changed the original additional MAP sensor which Turbo Technics used for the DCU from GM/Motorola to a standard 2 bar one as used on the Cossies (Weber Marelli) as the GM ones suffer from water ingress which stops them working. They use the same 5V supply and output an identical voltage relative to boost.

Originally, Turbo Technics used a couple of valves to make sure the stock MAP sensor didn't see boost. I think they went electronic as the mechanical system responded too slowly. I originally fitted a solenoid valve into the boost/vac line to the MAP sensor which was switched by a vacuum switch. It did work after a fashion but was too slow, it would drop into LOS if it boosted quickly. That's when I got in touch with Turbo Technics and got the frequency limiter.

Regarding the octane adjust to retard the ignition, Turbo Technics simply grounded all three wires in the adjust plug, including the idle speed raising one. After experimenting, I found that you could short out the octane adjust "on the fly" while the engine was running so I fitted a pressure switch to only switch the octane adjust when on boost. It made a hell of a difference to the performance off boost.