Jag XJR 4.0 Supercharged - Convert to LPG

[Guffer]

I have just converted my Omega to LPG and I am loving it. While talking to me dad he was wondering if his sorry looking jag can be converted. He cant afford to run it on petrol and is interested in LPGing it.

I have heard through another member that there are issues with converting this car, something to do with fuel return sensor and the ECU.

I would also be interested on thoughts about which injectors to use (as I suspect the run of the mill wont cope), where to tap the manifold and take the coolant feed.

If I can do this homebrew under a grand he may be interested (plus I'll get to use the car for a few months, the only reason I am interested in doing it tbh )

TIA for your input

[Tubbs]

There is a problem with the fuel return. There is also a magic box availiable to sort it. But it's fiddly. You need access to the petrol computer to set it up so you need an obd reader and the car needs to be obd compliant so you can see the petrol fuel pump pressure. You can also fit a fuel return but I have found they still put the light on. As far as a homemade convesion goes I wish you all the luck in the world. Once done they are good on gas. But getting there is quite complicated.

[redzed]

I had this fault code appear after converting my S-Type Jag which resulted in my car going into limp home mode. As Tubbs has said the solution is to fit a petrol return pipe, which in my case, I connected back to the petrol filler neck. I connected the solenoid valve to the same 12v supply that opens my under bonnet (pre vapouriser) solenoid and my tank solenoid valve. When your gas solenoids open to supply your engine with gas your petrol return solenoid also opens to send the unwanted petrol back to your tank. No more fault codes and the car runs perfectly on gas.

I know that there have been issues when the later supercharged 4.2 V8 engines where the coolant supply has been tapped into at the wrong location which can starve the supercharger of coolant which can obviously cause lots of problems. I'm sure though that the more informed will be along shortly with more information to help you.

[Guffer]

Thanks for the advice, I know its daunting but I am willing to get it done. By the way its the straight 6 4.0l, does this still have the fuel return issue?

Would normal injectors do the job?

What about vapourisers? Would it need twins or would a single do the job?

[martin rowe]

XJR is V8, you will need vaps that are suitable for 400 bhp.

[rossko]

XJR is V8

Some are, some aren't, I expect the OP knows what they have.

its the straight 6 4.0l, does this still have the fuel return issue?

Nope.
I'm not sure if you might run into the emulator issue on a late straight six, probably not.

Would normal injectors do the job?
What about vapourisers?

Depends entirely on what parts you have in mind.
You need injectors that can handle total bhp divided by six. About 320bhp? Its actually more demanding here being a six than an eight.
You need one or two vaps that together can exceed total bhp. Take claims of "our vaps do 400bhp each" with a pinch of salt.

You'll probably get to around a grand on parts-only costs for a proper job.

[exrm193]

I've just sold a supercharged 4 litre XJ....Are you sure its a straight 6?? If so, It's not supercharged so that might make the conversion easier?

All the superchargers were V8's

[Guffer]

I just went out and recounted the cylinder and yup it definitely only has 6 and a nice big supercharger. It's an N the year 97. Actually, I'm being cocky. I know what the car is lol

I am guessing twin gaps would require splitting a single feed from the tank to two.

[rossko]

Here's what the 'imaginary' 6 cyl s/c looks like
http://www.pistonheads.com/sales/2243324.htm
and while you can't believe everything in Wikipedia it does at least give details to check out
http://en.wikipedia.org/wiki/Jaguar_XJ# ... .931997.29

On the topic of supply lines, you would have to be particular about that too - nominal 8mm pipe.
There'd be an advantage in teeing off to two seperate shutoff/filters for twin vaps.
Ideally a 4-hole tank, but these are not readily available in best-case sizes for X300 wheel wells; a good quality multivalve should do instead.

[redzed]

Here's what the 'imaginary' 6 cyl s/c looks like

I'm glad that Mr Rossko knows his cars and Jaguar history.

[tommo2009]

from 94 - 97 the jag XJR's were a 4L straight six. from then on they were V8's

[lpg-jag]

To be honest I don't know much about the 6cyl jags, the fuel return issue is certainly present ont he V8's. I would have a search on the web and talk to some of the people doing jag conversions. Have you posted the question on some of the Jag forums. I found quite a bit of useful information that way.

I am running a V8 supercharged on gas on a single vapouriser just using the petrol top up option to meet the 400+hp requirements. The guy who did myconversion is running a non supercharged V8 with the same system just using less petrol so the Hp on the 6cyl shouldn't be a problem. Whilst some on hear will suggest that using this type of system is a bodge, unless you don't value your license how often do you realistically use enough throttle to cause significant pertrol usage?

Good luck, hope you find a cost effective way forward

[javers]

Guys, the jag variable fuel pump and return line issue is only a problem on the xj cars from the x350 (2003-onwards). I'm running my 98 v8 xjr on lpg with no additional return pipe etc. So with this one being a 6cyl 97 you should be fine with a "regular" type of conversion.

Jon

[Guffer]

I apologise if this is against the grain but I would like to resurrect this thread. I am fed up of waiting for my dad to make a decision so I am looking to buy one for myself and convert it. I am looking at either the 6cly or an early V8, thus no issues with the fuel return/trim issue.

My question is which kits are best for such a high demand engine? Do I have to run 15% petrol for those moments of right footed madness and what would it take to be able to run 100% LPG?

[rossko]

what would it take to be able to run 100% LPG?

It's only a case of buying the right rated stuff. Maybe if you can highlight what wasn't clear about looking at injector ratings, vap ratings, tank supply lines and valving, someone can expand on it?