My engine is a Jag 4.2 Straight 6, with tripple Webers, standard distributor with electronic ignition, and no vac connected due to the webers.

So my timing can vary by 8 degrees only on the centrefugal weights.

Currently performance isn't bad, but fuel consumption is really crap, less than 10mpg

I'm in the process of building a MJLJ edis 6 setup, with TPS, the TPS is the only bit left before I cut over, system tested and working so far.

The question is should I see any difference in fuel consumption and performance? my feeling is I'm currently running way off optimum timing, wondering whether I'm expecting too much expecting to get into mid teens mpg.

There must be some MPG gains to be had. I remember reading an article in the jaguar enthusiasts magazine a couple of years back where they managed to get over 40 mpg from a 4.2

Yep, using the 6x coil pack will see the spark voltage (60K) much bigger and help combustion.

Would be better to run MAP (using a reservoir) rather than TPS for fuel economy, though it should help a bit over a distributor.

But i was under the impression the TPS "calculates" what the map sensor would read, so should be broadly similar. It still gives increased advance at light throttle openings, which is what you want (when going somewhere, as opposed to driving)

The problem with tps is that it is quite inaccurate, one degree could equate to significant pressure variation (and so spark timing).
With extensive calibration of flow data tps could be as accurate, but in reality t is not.

Darren

I found that the biggest gains with MJLT were:

* It's easy to tweak the timing.
* Once set, it doesn't 'go off tune' like a distributor does over time.
* Starting is MUCH improved - assuming that the fuel is OK, if the engine is turning it WILL start, regardless of whether it's hot or cold outside.
* It gives a big fat spark at all times.
* It has a built-in 'soft' rev limiter, which is nice to have.

So, to answer your question, it won't give you an immediate gain if your old system was in a good state of tune. However, it will stay in tune, and if your existing system was below par then you will see an improvement. I did see a small gain in MPG, but that was lost when I started taking advantage of the more consistent performance (i.e. I put my foot to the floor more often! )

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Originally posted by cliftyhanger
But i was under the impression the TPS "calculates" what the map sensor would read, so should be broadly similar. It still gives increased advance at light throttle openings, which is what you want (when going somewhere, as opposed to driving)

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Thanks for the responses folks, is just as I've never done the conversion before to compare, built my last car with mjlj from the off.

Surely you could drill and tap (or braze) connections onto the weber manifold to get a MAP take-off? Just need a reservoir then to dampen the pressure fluctuations...

I found MJLJ made a huge difference for me when i was running carbs, this was mainly because my dizzzy/points etc were crap though. I drilled 4 small holes and brazed on take offs and used t pieces and a fuel filter to give me a reservoir.