Fuel injection system

(Harry Wilson) #1

Hello I was wondering if anyone can help me out. I’ve got a series 2 4.2 Xj6 from 1978 and I’ve found an complete 4.2 injection system off a series 3 and I’m wonder if I could put the series 3 injection system onto my series 2

(Robin O'Connor) #2

Everything is possible BUT when you say you have the complete system does that include the fuel return lines, fuel pump(s) ECU and any other items required to make the system work?

(Frank Andersen) #3

If the 78 is fuel injected, Harry - it’s a direct swap…

If the 78 is carbed - there is little point in switching, and complicated…

xj6 85 Sov Europe (UK/NZ)

(Harry Wilson) #4

No its a carbs setup on mine and how complicated can it be to do the conversion it would bring mpg up on my 4.2 engine

(Robin O'Connor) #5

As per my previous post, do you have all the set up from the donar car?
ECU, Fuel pumps, return fuel lines. There’s probably a whole lot more thats required but I don’t have a S111 to check against.

(Harry Wilson) #6

Cheers for getting back to me and I didn’t see your post but my jag is a series 2 4.2 straight 6 lwb for 1978 with carbs but my jag came of the same line as the pi versions of my jag and it was given the pi badge on the boot lid. I’ve got the fuel pumps and lines from my carb setup on my jag but does the petrol injection system need different fuel pumps the unit I’ve found is the complete inlet manifold with the full injection system with out the injection computer. I’m only enquiring as Im hoping it will give me more mpg.

(RustfreeMike) #7

Hi Harry - You can’t use your original carburetor fuel pumps as you need a PI pump that will supply 36psi. The carb pumps only supply 2-4psi. You would need to replace all rubber lines with PI lines that will withstand the additional pressure as well as a PI filter. You’d need to plumb return lines and switch over valves to both tanks if you go with the original style system. Gotta have the ECU (computer) and all the wiring harnesses associated with it…

It’s certainly doable but it’s fairly complicated and you have to be sure you have all the parts and everything is in good shape to make it as painless as possible.


(Frank Andersen) #8

The gain with EFI will be minimal, Harry - milage from well trimmed carbs are almost the same…

As Mike says; ‘it’s doable’ - but warranted only as challenge or labour of love…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Doug Dwyer) #9

I was wondering about that and was gonna ask how much improvement was expected.

For some persepctive, and to perhaps help gauge the effort-vs-benefit, my Ser III XJ 4.2 FI…my daily driver for many years…delivered about 12 mpg in city driving and about 20 on the open road if I was fairly gentle. USA gallons, BTW.


(Robin O'Connor) #10

My ‘75 4.2 S11 returned 22mpg (imp) on a run last year with carbs that are somewhere around ‘tuned’ I suspect leaking spindles. It is impossible to get the idle down when in neutral. And I wasn’t hanging around at times :slight_smile:

(Doug Dwyer) #11

Your 22 mpg (imperial) results are in line with my 20 mpg (USA) results.

Personally I’d prefer F.I. over carbs for a variety of reasons. I think the conversion would be a fun project, so there’s that. But if better fuel economy is the only motivation for the conversion I’m not so sure it’s really worthwhile, considering effort/time/expense.


(Frank Andersen) #12

I suspect the difference will be ‘drowned’ by other factors, Doug…

Like driving style - and indeed less than perfect set-up of either system…?

xj6 85 Sov Europe (UK/NZ)

(Harry Wilson) #13

Okay thanks everyone for all th information

(Harry Wilson) #14

On another note this is for when I get her on the road she’s still got a load of welding that I’m doing also you wouldn’t know anyone who makes full floor pans at a fair price and where I can get the kick plates. But what I can tweak to get better fuel economy my jag is a series 2 Xj6 4.2 from late 78 was on the pi line but got hif7 put on her.

Also not sure what it’s called but where could I get the rear different arm plates and thanks everyone it’s been a great help on this site also how fast should my engine spine on the ignition she’s not for starting but the spin seems slow to fire the engine as I’ve been able to get her to pop but she won’t fire yet.

(Robin O'Connor) #15

Cranking speed is only going to be in the region of 200-250rpm at a guess.
Is this the part you are looking for?
Page 13

(Harry Wilson) #16

Aye thats the one mate the plate has rusted off the floor or chassis for where the donut bush bolts to

(Harry Wilson) #17

And so it’s a pretty slow crank then just checking is case there is a rust ring around the piston or rust along the bore as she has sat in a shed for 25 years I got her abit over a year ago and I’m getting there with her also you wouldn’t know how they painted cotswold blue dark as I’ve be unable to find a color match for my jag. If you check Peter vardys Daimler series 2 Xj6 is the same Cour as mine

(Frank Andersen) #18

Have oiled the bores, Harry - and liberally cranked without the spark plugs to eliminate residual rust…?

Slow cranking may have lots of causes, including iffy battery and starter - or connections. And indeed; have you checked compression - and with what result…?

xj6 85 Sov Europe (UK/NZ)

(MarekH) #19

The v12 cranks at 120rpm with a Lucas starter motor or 160rpm with a gear reduction motor. With plugs out, it’ll be about 40rpm faster.

Your car will probably be in the same ballpark. There is no need to crank faster as it is the fuelling which makes it fire up and start. (There is a reasonably wide latitude in spark advance by comparison.)

Given the above, there is no point cranking until you have good fuel pressure.

kind regards

(Mark Lee (Pay Pal Patron)) #20

For what ever it’s worth it’s called a radius arm which are available new. The mating service for the big end radius arm bushing is called the radius arm cup. These are very much available. SNG Barratt has in stock, the Part number is JS254

Depending on your location, In the North America; on the east coast everydayxj.com is a good source as well as Jaguarheaven.com on the west coast. In europe david manners - Jag spares is another good source for parts.
If you look, you can pretty much find what you’re looking for. Floors can be found but their not cheap. The last time I looked for a XJ6C it was $400.00 (a side) US money. Depending on your skill level; sheet metal and a shrinker stretcher and a bead roller is a good investment. :slight_smile: