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RPMs are not correct
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Post RPMs are not correct 
I have a 1296 Triumph Spitfire with the Megajolt ignition system. This car is under restoration but when I first put the Megajolt system on it worked fine and I fine tuned the map and all was good. A few days ago I fired up the engine and it ran rough. I took it for a spin within my farm and it started to run really rough. Parked it and when I restarted it, it would pop and try to run but would not start.

I replaced the Crankshaft sensor and found a suspect poor ground to the EDIS and MJ. It started right up BUT with the computer connected to the MJ, I see an rpm difference between the mechanical tach and the MJ computer program. At 3500 rpm on the Tach the software showed 2500 rpm. At idle the tach showed a little over 1000rpm and the MJ program showed apx 800 rpm.

The map is of course tracking the MJ but I have rough acceleration now and some popping at the higher rpms whereas I did not have any of this before.

It seems there is a hardware counter that is not dividing properly in the MJ. Any ideas as to what could be wrong???

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You can check the cylinder count to ensure it's properly set to 4 / 6 or 8 cylinders. When you change the cylinder count it will affect the RPM reading, you can actually observe it in the software while running after making the changes.

Regarding your question if there's a problem with an internal clock or timer then it will *also* affect the baud rate of communications link to the computer, since they all derive from the same clock. So; if the software can communicate, then the RPM measurement is also correct.

Hope that helps!

Brent Picasso
Founder, Autosport Labs
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