Jaguar XJ-S. Manual - part 59

 
 

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FUEL SYSTEM 

 

The D-Jetronic XJ-S fuel system involves a fuel tank with a drain that feeds a small surge tank.  A screened pickup in 
the surge tank leads to a soft-mounted fuel pump just below and to the right of the spare tire.  The line leads to a fuel 
filter and then to two separate fuel rails on the engine, one for the left bank and one for the right.  A pressure regulator 
on each rail directs excess flow through a fuel cooler and then back to the tank. 

The Digital P uses a similar system except that the two separate fuel rails were replaced with a single rail.  There are 
still two pressure regulators, but in this case one is a supply regulator and one is a return regulator.  Supposedly the 
return regulator, the one on the LF corner of the engine, is the only one that actually does anything.  While the D-
Jetronic regulators held rail pressure constant, the Digital P regulators vary rail pressure with intake manifold vacuum 
and therefore have vacuum lines connected to them. 

The earliest saloons are fitted with carburetors, which use much lower fuel pressure than EFI.  The EFI saloons have 
fuel systems resembling those in the XJ-S.  The most notable difference in the saloon fuel system, though, is that the 
Jaguar saloons have two fuel tanks and a switchover system so the driver can choose which tank to use. 

In 1992 the XJ-S fuel system changed markedly.  The external fuel pump was replaced with a submersible pump inside 
the tank.  The fuel rails were redesigned to connect to the injectors with O-rings instead of short hoses.  The worthless 
supply regulator was omitted. 

 

 

Fuel Fires

 

 

Besides the usual general concerns about fuel fires -- fuel lines left in place too long until they rot, etc. -- there are also a 
couple of specific worries: 

 

EARLY D-JECTRONIC FUEL RAIL:  The early Digital P XJ-S’s (early 80’s) had a problem with engine fires.  There 
was a recall to address the problem in which the fuel rail on the engine was replaced; the newer design is indicated by 
rectangular tubing, while the pre-recall rail was made of round tubing.  All Digital P XJ-S’s were subject to this recall, 
but indications are the recall was not as conscientiously applied outside the US.  Unfortunately, word is that the recall is 
“closed” and dealers will no longer perform it.  If you have a Digital P with round tubing in the fuel rail, you probably 
should consult your favorite junkyard and collect all the parts that look different and perform the recall yourself.  Note 
that the D Jetronic still uses fuel rails with round tubing. 

Leaking fuel in an engine compartment is remarkably difficult to ignite.  Usually there have been obvious odors and 
visible leakage for some time.  Please do not ignore fuel odors; the XJ-S shouldn’t have any. 

 

MARELLI IGNITION WIRES:  The later XJ-S with Marelli ignition also has a reputation for engine fires.  Peyton Gill 
reports on “an XJ-S that had a little pyrotechnics under bonnet.  I asked the guy about it and he said that the fire was put 
out within 30 sec (owner had a fire extinguisher) and the estimate to repair was $2000.00.  There was not that much 
damage.  The cause of the fire was the ignition coil wire was about 1/4 inch from one of the fuel injection lines 
(between rail and injector).  The ignition wire had been arcing to the line and eventually worked its way through.  I 
guess the physical damage and ozone created by the arc eventually broke down the line.” 

Julian Mullaney adds, “There was a recall for cracked injector hoses and injector bodies.  Ozone from the distributor 
leads causes the perished plastic.  The recall replaces the lead with a shorter one, and replaces the injector.  They looked 
up my car (vin no.) in their database and the fix had already been done a long time ago, however the problem persisted. 

 
 

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“The problem was ozone deteriorating the injector hose on the right bank second cyl. from the firewall.  It produces a 
cracked surface of the rubber hose.  You should look carefully for this, it's not easy to spot.   

“The dealer said that they were instructed to look for visual damage to the hose and replace injector if needed.  "If" is 
the key word here.  However, if it looked good, they could get away with only changing the HT lead to a shorter one 
(thus not close to the injector) and leave the original injector hose.  This leaves the chance that damage could have 
occurred to the hose but it's not visible yet, leading to the following chain of events: 

upon initial recall they only replace the HT lead  

then the hose continues to deteriorate from initial ozone embrittlement; 

then you see the damage to the hose a year or two later; 

pyrophobia sets in; 

then you call the dealer; 

then they tell you sorry, the fix has already been done; 

then you find that the recall was done sloppily; 

then you get pissed off; 

 

a) 

then you think about fixing the problem yourself 

 

b) 

you call the dealer again and insist they fix it again properly 

 

 

 

then dealer calls Jaguar to authorize 2nd repair 

 

 

 

they say OK 

 

 

 

you get it fixed for free 

“Option b) worked fine with me, my local dealer was very good about it.” 

Ron White adds, “I checked the recall database and the recall only affects 1989-91 XJ-S models; this is a result of:  
"The high tension lead from the ignition coil can move from the production location closer to the #4A fuel injector 
hose.  Vehicle description:  coupes and convertibles with Marelli ignition systems."” 

 

MTBE:  Stephen Wood says, “We starting in Spring 1996 having a substance called MTBE -- methyl tutol-buytol 
ethanol, something like that -- blended with our gas to help reduce emissions.  Hopefully they will be taking it out soon, 
as there has been a major hubbub about it here.  You see, it also melts things, like fuel lines, carburetor gaskets, 
(especially the old rubber/cork type), fuel tanks, brazing material solder, etc. 

“Last summer car fires were up significantly all over the state, including my brother’s ’69 Camaro (it was restored).  
MTBE melted through the carb gaskets on his vintage Holley and poof. 

“At that point it got serious, and I checked my fuel lines, and sure enough, they were going way squishy from the inside 
out.  In other cars we have seen it also has melted injector seals. 

“If you ask the insurance companies they have had a slight increase but nothing to worry about.  No problem, right?  
Wrong!  Most of the cars affected are cars that the insurance industry won’t provide fire, theft and vandalism coverage 
on anyway.  If you ask the CHP and the firemen, they know that last summer was a major problem.” 

So, you need a new type of fuel hose, right?  “The problem with the hose issue is that the rubber manufacturers are not 
going to gear up for a California-only issue.  However, some of the new cars have fuel lines made out of a tygon 
derivative, a newer plastic that is more resistant to these blended fuels (New LT1- LT4- and LS1 GM motors).  I don't 
think there is a crossover app. as of yet, tygon is a bitch to work with and has the characteristics of polypropylene 
tubing, i.e., firm and not clampable.  You have to use special fittings with it. 

 
 

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“There is supposed to be some new silicone-based flexible "rubber like" fuel line coming out soon from Gates or 
Goodyear but I haven't seen it.  So for now, I have been keeping an eye on the situation and checking all pressurized 
fuel lines every month, and replacing them every 6 months (I have done this three times now).  Vent lines are ok from 
when I replaced them 6 months ago.  I have been changing fuel filters every 45-60 days (preventative mania), making 
sure to cut open the old filter to see if anything weird develops like little bits of rubber hose. 

“I will have to take my gas tank out this summer, and have it boiled and welded or just put in a new one.  The corrosion 
around the outlet is growing and I think it is melting through the solder.  I may just JB Weld it or something.” 

 

FIRE EXTINGUISHERS:  After reading this book, you have probably come down with a healthy dose of paranoia 
regarding fires in the XJ-S.  A fire extinguisher is cheap, and may come in handy. 

Ron White had a fire in his car, and thanks to having a fire extinguisher in the trunk and knowing how to use it, his car 
survived with almost no damage.  “I have seen engine fires in other cars and have seen people make the mistake of 
flinging their hoods (these were American cars) open, only to have the fire flare up 5 or 6 feet because of the added 
oxygen.  I opened the bonnet just enough to get the nozzle of the extinguisher in, and gave it a good squirt.  I then 
cautiously opened the bonnet up and seeing no flames opened it up all of the way and gave it a real good squirt!”  
White’s extinguisher happened to be a Halon type which works wonderfully and leaves no crud on the engine but is 
bad for the ozone layer and is in the process of being outlawed.  Experts seem to feel that a common powder type fire 
extinguisher would probably work just as well, the only disadvantage being that you’d have a job getting all the powder 
out of the engine compartment afterward. 

One more note:  White’s car is an ’86, meaning it’s late enough to have had all the updates to correct the early fuel rail 
problems and too early to be covered by the recall for the later cars with the Marelli ignition.  “It appears that the cause 
was a cracked body on an injector, and it was squirting fuel directly on the distributor!”  That fire extinguisher is 
sounding like a better idea all the time, isn’t it? 

John Napoli suggests a built-in system like those found on race cars:  “It should be a lot easier to extinguish a fire 
within the closed confines of the engine compartment with the bonnet closed, and you could certainly react a lot 
quicker than, say, opening the bonnet, saying "Oh, sh$t", running for the boot, trying to find the fire extinguisher that is 
underneath all your luggage, meanwhile the bonnet is open and the flames are getting higher...”  Of course, keeping the 
extinguisher on the floor in front of the front seat may help. 

Emile A. DesRoches says, “If anybody is really interested in a real "racing car" fire control system (sanctioning bodies 
require a system plumbed in to spray at the engine, fuel cell and driver's lap area), they can be obtained from such 
organizations as Racer's Wholesale in Atlanta.  From experience as an SCCA tech inspector, I can say that they may 
make a mess, but they work and clean up is inevitably less expensive than replacing a fried V12 motor.” 

 

 

Fuel Odors

 

 

FUEL ODORS:  To state what should be obvious:  Jaguars are not supposed to smell like fuel. 

One excellent suggestion is to trot the car right down to your local Jaguar dealer, or anyone else with the equipment to 
test automotive emissions.  The testing equipment includes a probe that is inserted in the tailpipe to detect unburned 
hydrocarbons (fuel).  This probe is real handy for finding fuel leaks anywhere in the car. 

There is a relay in the trunk through which the EFI controls the fuel pump; it’s the one without a red paint mark on it.  
You can remove the relay and jump connectors 30 and 87 in the socket to run the fuel pump.  This is useful for 
searching for fuel leaks without having to leave the engine running.  Of course, you’ll kill your battery if you do it for 
too long. 

 

 
 

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FUEL ODORS IN TRUNK:  The trunk smelling of fuel is a common problem with many common causes:  

ƒ  fuel-soaked carpet padding (see page 234) 

ƒ  leaking hoses either in the trunk or over the IRS (see page 234) 

ƒ  leaking compression fittings (see page 235) 

ƒ  someone installed the wrong type hose in your fuel system (see page 237) 

ƒ  there may be a bad O-ring in the fuel filler connection (see page 243) 

ƒ  a plugged or disconnected drain from the fuel filler compartment (see page 243). 

ƒ  a tank that develops a hole by rubbing on a steenkin’ rivet (see page 244) 

ƒ  a tank that has developed stress cracks (see page 244) 

ƒ  a tank that has simply rusted through (see page 244) 

Note that you can greatly reduce the possibility of fuel leaks or odors by addressing all of these concerns at once!  Take 
the tank out, coat it outside and in, replace all fuel and vent hoses with new, and reassemble.  It would take a few days, 
largely because lining and coating the tank require several steps of cleaning and coating and letting them dry overnight. 
 If you’re not willing to try lining the inside of the tank yourself, doing all the other tasks would still be worthwhile. 

Don’t overlook the possibility that fuel odors in the trunk aren’t originating in the trunk.  The author had a leak in a line 
under the car, and couldn’t smell it outside the car but it stank somethin’ awful inside the trunk.  I couldn’t even 
imagine how the fumes got into the trunk.  Likewise, a malfunctioning vapor recovery system (see page 257) that’s 
releasing fumes into the bodywork up at the front of the car may result in the fumes migrating into the trunk.  In fact, 
even a cylinder misfiring and releasing unburned fuel out a tailpipe has been known to cause fumes to collect inside the 
trunk. 

People who correct problems with the vapor recovery system often report that it cures odor problems in the trunk.  If 
the problem was a stuck-open (or missing) Rochester valve overloading the carbon canister and as a result odors were 
coming from the carbon canister up front and were working their way through the bodywork to the trunk, they may be 
truly cured.  Likewise, if the problem was a leak from the vapor recovery system somewhere, it may be truly cured.  
But if the problem was a plugged vapor recovery system causing excessive pressure in the tank, the problems are not 
cured, they’re just no longer as apparent.  The vapor recovery system is supposed to prevent excessive pressures within 
the tank, and if it fails the pressures may reach levels that force fuel through leaking fittings or even crack the tank.  If 
the vapor recovery system is fixed and the pressures are no longer excessive, there may be far less fuel coming through 
the leaks -- but the leaks are still there.  And any cracks that may have started in the tank are still there, too.  If you 
could smell fuel, that fuel was getting out somewhere, and it would behoove you to find out where. 

 

SMELLY CARPET PADDING:  The fuel filter is the size of a Coke can and is located behind the spare tire in the 
trunk.  When this filter is replaced, it is all too easy to spill its contents within the trunk.  The nature of the foam 
padding under the carpet is such that once this happens, your trunk will smell of fuel for all eternity.  The only 
suggested fix is to replace the carpeting and padding.  It is recommended that before the filter is replaced, and before 
any repairs to the fuel system in the trunk are carried out, the carpet be removed. 

When changing that filter, unscrew the mounting bracket from the floor first.  Then you can hold the filter over a catch 
pan when disconnecting the hoses. 

 

LEAKY FUEL LINES:  As described on page 242, there are several fuel lines that include a piece of hose in the middle 
of a metal tubing assembly.  When old, these hoses often weep fuel rather than burst outright.  In fact, they may leak so 
slowly that they never appear wet; the fuel evaporates faster than it leaks.  Just about the only indication of trouble is 
the odor.