S Type fuel leak

Post Reply
Message
Author
Yorkie15
New member
Posts: 7
Joined: Thu Dec 20, 2018 8:14 pm

S Type fuel leak

#1 Post by Yorkie15 » Fri May 01, 2020 8:27 pm

Hi
My S Type has a BRC system and has performed well for me until now. The problem I have is the car has not been used for the past 5 weeks and when moving it off the driveway there was a massive petrol leak from the tank area. Now this probably has nothing to do with the lpg system but Ii have tried to locate the leak and it is running down the inside (axle side) of the nearside tank. Looking from underneath there is nothing that can be seen that could account for it and I have removed the rear seat cushion and there are inspection points for the fuel pump and transfer pump and there are no leaks visible.

My question to the forum is that when the system was installed would the fuel pipe have been diverted via a shut off valve for when the car is running on lpg? If so would this be located at or near the petrol tank?

To be able to see more of the pipework I think the petrol tank will need to be removed or at least lowered which will require the propshaft to be removed and quite a bit more and this is beyond my capabilities now.

The strange thing is that the leak only occurs with the engine running not with just the ignition on which of course runs the pump and pressurises the system so why no leak then? The leak is so bad that driving to a garage would be unsafe and so an expensive transporter will be needed when the lock down ends

Any help or advice will be most welcome.

LPGC
Installer
Posts: 3809
Joined: Wed Sep 29, 2010 6:01 pm
Location: Yorkshire
Contact:

Re: S Type fuel leak

#2 Post by LPGC » Fri May 01, 2020 9:15 pm

Most S Types (except perhaps very early ones) run a return-less petrol system (on most other fuel injected engines a mechanical fuel pressure regulator bleeds excess fuel/pressure back to the petrol tank via a fuel return pipe). An S Type with a returnless fuel system has an electronic fuel pressure sensor that's part of a feedback mechanism to keep fuel pressure correct by controlling the duty cycle of the petrol pump - the petrol ECU compensates petrol fuelling (petrol injector duration) for above/below standard fuel pressure. Running on LPG means no petrol is used but the petrol pump even running at minimum duty cycle power will increase petrol rail pressure to well above normal (petrol operation) pressure, and since the LPG system works as a slave to petrol injector pulse duration this high petrol pressure reading means the petrol injector pulse durations when running on LPG would be shorter than normal. The fuel pump working at such high pressure can be damaged, the high pressure reading can cause several problems in itself and the shorter petrol injector pulse duration readings can cause problems for running on LPG (because the LPG system works as a slave to petrol injector pulse length readings).

It's very likely that the leak is on a part of the petrol system that was modified by the LPG installer (modified to fit in a physical fuel return that will keep fuel pressure and thus fuel pressure readings within the normal range).

On some X / S Type Jags fuel return components may be fitted by an LPG installer on top of the tank (pump access panel below rear seat). If you can't see where the leak is coming from (just petrol running down the side of the tank) I'd suggest looking there first.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Yorkie15
New member
Posts: 7
Joined: Thu Dec 20, 2018 8:14 pm

Re: S Type fuel leak

#3 Post by Yorkie15 » Fri May 01, 2020 10:12 pm

Many thanks Simon for the response.

When looking at the pump access panel (drivers side) only the electrical connections and one fuel feed pipe with quick connector which is about 10mm dia plastic can be seen

In the transfer pump side (nearside) there is only an electrical connector to the pump as I understand fuel is transferred from side to side internally within the tank. However, at the side I can just see a plastic pipe that looks like the feed pipe from the other side and there is a T connector from this to 2 larger rubber pipes that disappear in different directions.

I cannot see where these go to from either above or below and to fit them the fuel tank would have had to be dropped. Would they go to this trouble when installing?

My car is an '03 and as you rightly say has no return engine to tank.

I still don't understand why it only leaks with the engine running, nothing with just ignition on.

It would be useful if I could force the car to run on just gas, I could at least drive it then to a garage but as far as I can see the BRC system does not cater for this.

Howard

LPGC
Installer
Posts: 3809
Joined: Wed Sep 29, 2010 6:01 pm
Location: Yorkshire
Contact:

Re: S Type fuel leak

#4 Post by LPGC » Sat May 02, 2020 3:44 pm

Even running on just gas it's still likely to leak. It's unlikely that the installer wired in a petrol pump shut-off, if they did wire in a petrol pump shut-off they'd also have to wire in a petrol pressure emulator.

Since the car doesn't have a fuel return the only petrol pipes that aren't in the engine bay should be the engine feed and a petrol vapour pipe (for the evap purge system), any other pipe (or anything that doesn't look factory) would likely be part of a petrol return fitted by the LPG installer.

As said though, the install might not have a fuel return - it's possible that the LPG install just has an electronic petrol pressure emulator. In which case the petrol leak probably wouldn't be related to the LPG install (unless the installer damaged something).
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Yorkie15
New member
Posts: 7
Joined: Thu Dec 20, 2018 8:14 pm

Re: S Type fuel leak

#5 Post by Yorkie15 » Sat May 02, 2020 6:07 pm

Thanks again for the response, I will have to arrange a tow or transporter then to a garage.

Howard

Yorkie15
New member
Posts: 7
Joined: Thu Dec 20, 2018 8:14 pm

Re: S Type fuel leak

#6 Post by Yorkie15 » Tue May 19, 2020 9:41 pm

To close the loop on this, the car was taken to my local Jag Indy who dropped he fuel tank and found a split pipe that had been installed by the LPG fitters to emulate the fuel return when running lpg. The pipe was plastic and routed very close to the exhaust heat shield. They have replaced with copper and also repositioned a valve in this line which was near the tank as they considered it should be at the front of the car not the rear (something to do with fuel pressure?). Anyway car is now back where it belongs and ready for use again whenever we are allowed to travel again.

Thanks Simon for your help with this problem.

Howard

Brian_H
Intermediate Member
Posts: 1671
Joined: Mon Jan 23, 2012 12:21 pm
Location: Milton Keynes

Re: S Type fuel leak

#7 Post by Brian_H » Tue May 19, 2020 9:44 pm

Would make sense to have the shut off near the engine, else the fuel pump has to pressurise the length of the car in pipe again when its on petrol operation, so seems like they thought about it before fixing it. Also would mean if you had the same failure in future, that you could use that valve to isolate most of the return as well.

Thanks for replying to confirm your issue though, as it might help someone in future.

LPGC
Installer
Posts: 3809
Joined: Wed Sep 29, 2010 6:01 pm
Location: Yorkshire
Contact:

Re: S Type fuel leak

#8 Post by LPGC » Wed May 20, 2020 1:02 pm

You're welcome Howard

If the petrol system is tapped into (for the fuel return) in the engine bay it certainly makes sense to fit the petrol solenoid in the engine bay for ease of access and also to prevent having another pressurised petrol pipe running under the car (if the fuel return metering jet is fitted to the input side of the fuel return solenoid the return pipe under the car will only be at very low pressure unless it gets blocked)

But on some of the Jags it's possible to tap into the engine's feed pipe near the tank, thus avoiding running a fuel return pipe under the car altogether, in which case the petrol return solenoid has to be fitted near the petrol tank. Still it makes sense to fit the restriction jet on the input side to the solenoid.

Years ago petrol return system pipes could use LPG pipe but ethanol in more recent petrol turns LPG pipe into mush.
Some petrol pipe supplied with 'fuel return kits' from LPG suppliers is closer to carb spec petrol pipe than fuel injection pressure rated petrol pipe, it won't turn to mush but can balloon and burst under fuel injection system pressures (especially on engines that run high fuel injection pressure e.g. 5 bar like some of the Mercs). Such pipe may be OK to use on the post jet leg of the fuel return system (low pressure side) but not on the pre jet (high pressure side). Still it's a good idea to avoid using low pressure rated petrol pipe on any part of a fuel return system. I wouldn't use petrol pipe rated at less than 8 bar on any part of a fuel return system and I wouldn't use any cloth braided type of petrol pipe.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Post Reply