Oct 162015

Default 4.2 ignition mapping

The EDIS Megajolt electronic ignition kit for the 4.2 engine was supplied with an ignition mapping that closely replicated the advance curves of the original Lucas 22D6 distributor.

The aim is to produce a mapping tailored to my actual engine by taking it to a professional outfit with a rolling road. Although I’ve been told it’s not for the faint-hearted. The engine is taken through its paces with sustained running all the way up to the red line!!

For now, I’ve followed a suggestion from the E-Type forum to load different mappings into the Megajolt controller to compare. A number of owners have produced maps for their engines and uploaded them to the forum for others to try. As the controller can store two different maps at any time, a discreet switch has been mounted in the glovebox to enable switching between two maps.

Checked into the Jaguar specialist
for further investigation

Although the final tuning and mapping is some way off as neither the garage that did the MOT nor Powerbell, a local independent Jaguar specialist, had been able to tune the carburettors to get the engine running smoothly. The latter suspected there might be either sticking valves or valve clearance issues which would require further investigation.

The engine had sat without being run for quite a long time since being reconditioned by VSE, which is far from ideal. The plan was to run the car for a while to see if the layup had resulted in a slightly sticking valve which might clear with use …. ever the optimist! Alas it didn’t! So the car was returned to Powerbell to get to the bottom of the rough running.

The first task was to perform a compression test and measure the valve clearances. The manual indicates that the expected compression pressures are 150psi for 8 to 1 compression ratio and 180psi for 9 to 1. The test showed mine were way off and in some cases almost non-existent:

Cylinder: 1 2 3 4 5 6
Pressure: 125 130 125 120 65! 10!!

The thicknesses of the valve adjusting pads under the tappets were miles out so everything was far too tight. The guys at Powerbell were shocked that they could be so far out in a newly reconditioned engine. Had I not decided to get it resolved now, they said the likelihood would have been burnt valves and a much bigger problem to resolve.

The compression test revealed very
low pressure in cylinders 5 & 6
Calculating the correct thickness
for the valve adjusting pads

I was relieved but at the same time not impressed with VSE who had rebuilt it. Unfortunately it’s way past the standard one year warranty they offer but I’ll not be using them again. It really shouldn’t be necessary to correct a simple measuring job that could have had expensive repercussions.

Removal of the camshafts to correct the valve clearances … on a newly reconditioned engine!

It was with some anticipation that I headed off to pick up the car when the call came to say it was ready. I really didn’t know what to expect but it had been transformed! It was now able to idle at the intended 700rpm, the rockiness had gone and it was running so smoothly.

They did recommend putting on another 1000-1500 miles on the clock, so the engine is properly run in, before mapping the ignition on rolling road.

 Posted by at 8:45 pm