Megajolt ECU

The megajolt is a fully mappable electronic ignition system that you can either build from a kit or buy ready built. It uses the ignition module, coil pack and crank position sensor from an early 1990s sierra/fiesta/escort/mondeo and a toothed wheel attached to your crank pulley. By using an iginition system such as the megajolt you get much more accurate timing than a dizzy can ever hope to provide, you also get complete control over the timing at every point rather than having to compromise between top end power and low end tractability.

The toothed wheel effectively replaces the distributor and tells the megajolt where the engine is in the cycle. The megajolt uses the engine speed and either a throttle position or manifold pressure sensor to calculate how much advance you want and by watching the toothed wheel fires the coils at the appropriate moment. The coil packs used with the megajolt are wasted spark, which means that there are two coils in the pack, each coil is conencted to a pair of cylinders - 1+4 and 2+3. Because the cylinders are wired up in this way you get two sparks per cycle, one on the combustion stroke and one on the exhaust stroke, this second spark being "wasted".

Tuning of the megajolt can be easily accomplished by connecting up a laptop to the serial port and running software that you can download from the web. The base map that comes with the megajolt should be good enough to get the engine started, however you should put a proper map in place before driving around. A number of people have made their maps available one of which should be a good match for your car but fine tuning will always be beneficial. With some care you can tune the ECU on the road by timing the acceleration between two speeds on a flat bit of road, however mapping on the rolling road is the quickest way to get a perfect setup.

In terms of installation, he toothed wheel can either be done by machining your existing crank pulley or using an off the shelf toothed wheel and either bolting or welding it to your pulley. If you've got a flip front then it's easy to get at the crank pulley to remove it for machining. If not then if you don't want to pull the engine out move the radiator out of the way, put a jack under the sump, loosen off the engine mount and drill a 10mm hole in the inner wing. Through this hole you can insert a socket extension and an impact driver will make light work of the bolt. Your local machine shop will add 36 5mm teeth to your pulley for 20 quid.

Once you've connected the megajolt/sensors/coil and ignition module up all you need to do is to connect power, ground and a wire to the white/black wire that feeds the tacho and you can fire it up. If for some reason there's a problem with the megajolt the ignition module will go into failsafe mode and provide a fixed 10 degrees advance.

Once it's started a good trick to get a really good idle is to give some extra advance above and below your desired idle point - if you're idling at 1000rpm then run say 14 degrees at 500 rpm, 12 at 1000rpm and 14 at 1500rpm. What this does is give the engine a little boost if the idle drops below 1000rpm, compensating for any temperature changes.

The ford coil packs use a different connector to the dizzy so you'll need some new plug leads, I bought some fancy silicone fiesta ones off ebay for a tenner.

Once it's all running happily you can remove your dizzy and plug the hole, I used a broken old dizzy, cut down with a bolt through the center. If at any time you want to revert back to the dizzy you can just plug it back in, reconnect the leads and off you go.

As long as you can solder building a megajolt from a kit isn't difficult and takes an hour or two. If soldering isn't your thing you can purchase fully built systems from

Pictures of my installation.

More information on the megajolt can be found on these sites:

G2 home Chris' homepage

Chris Good