Injection System Stuff


Ever wondered what was inside the Injector Power Resistor module?

Not much, actually! The resistors are formed by copper tracks on the circuit board; you can see them meandering around on the lower picture. The 2PR module is generally reliable; any problems tend to be related to the connector block or the wiring loom connector. Replacement crimp terminals are easily obtainable (try Vehicle Wiring Products) to allow a damaged or corroded connector to be repaired.




Two views of the larger-bore Jaguar airflow meter. The black mounting bracket and the alloy collar for the outlet air hose were fabricated by me. Poor picture quality due to the cheapo digital camera I had at the time!




The airflow meter is a precision unit, but it's not actually THAT complicated to work on. Whilst I don't advocate that the AFM should be taken to bits for the hell of it, if you're going to do it, you may find my stripdown sequence useful...

I decided to have a crack at building an injection system to my own specification. That is to say, an attempt to optimise what I already had rather than an aftermarket ECU and associated sensors. There are those who insist that the Lucas system can't be tuned for much improvement, but several successful racers since the 1980's can't all be wrong!

Now I don't claim to be any sort of expert, but luckily I had a chat with Mark Adams, who is. He told me that the airflow meter would have been matched to the rest of the system and that NCK stamped their engine number on it. Whether they did or not I can't say, but my car had had its AFM replaced at some stage so it was almost certainly not optimised. Further, I'd replaced it with the Jaguar unit and merely adjusted it by trial and error to get what I thought was the best compromise - hardly a scientific way to optimise anything!

Mark suggested that the Jag AFM would tend to cause the mixture to be too lean. I pondered whether the quickest fix was to throw in more fuel :-D A search on Ebay turned up a guy selling brand new Jaguar fuel injectors in sets of 6. The maximum flow rate was some 40cc a minute more than the 180cc of the standard injectors, a worthwhile increase. I emailed him to ascertain that he could supply me with 8 and ended up getting a full set for less than 60 - well worth a fiddle, I thought!

For some obscure reason I convinced myself that NCK hadn't done any porting work on the inlet manifold and decided to have a go at opening the ports out on a spare manifold that I had. This proved to be quite easy but rather tedious and messy. Then I took the injection system off the car and discovered that, of course, NCK had opened the ports out - quite radically, in fact!

NCK's porting work (at left) compared with a standard manifold:

... and my first attempt at porting (on the right); outline round port at left is taken from the gasket...

From discussions I'd had with various people in the Wedge community I knew that another worthwhile mod. was the addition of an insulator between the trumpet base and the inlet manifold. This reduces heat soak into the inlet tracts and should allow a cooler, denser air charge. Of course it would also add the thickness of the insulator to the inlet tract length, so I opted to shorten the trumpets by an appropriate amount to compensate. This has the added benefit of increasing the gap between the centre four trumpets and the inside of the plenum chamber top, apparently allowing better airflow at high rpm. Then another issue surfaced; that of under-bonnet clearance. Another few millimetres might just be enough to prevent the bonnet closing! I decided to mill the bottom of the trumpet base down by the thickness of the insulator, which would maintain the port lengths whilst avoiding clearance problems. Of course the shortened trumpets would now change the engine response, but I had plenty of spare trumpets if I didn't like it!

Plenum insulator machined and being tried for fit:

Bank of new injectors installed:

Shortened trumpet base on left, with a standard item for comparison:


The castings were also tidied-up a little to get rid of casting flash, Land Rover logos etc., and the parts given a coat of what Halfords call 'metallic black' but what looks more like graphite grey to me (Edit March 2013: this paint is actually good stuff, very hard-wearing!):


One possible modification is to bore out the throttle body to accept a larger-diameter throttle plate: another way that has also been implemented (and one which I fancy trying) is to chop off the existing throttle body, weld on a square plate suitably drilled to accept the throttle body from another car.... and it so happens that there's a Jaguar unit that looks very promising! Watch this space ... in the meantime, this is what my engine bay looks like with the 'project' injection system installed:

...and the proof of the pudding of course is on the dyno, where with my guesstimated injection system 'set up' by the seat of my pants the car made 256bhp at the flywheel, with 280lb.ft. of torque. However the most pleasing part was the air:fuel ratio, which looked like this (204bhp being the figure at the wheels):

I guess the next logical step is to reinstate the NCK-worked inlet manifold etc. and see how many more of the claimed 275bhp might be available ;)


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