I've read several threads about fuel pump issues, where one of the tests for XJR owners is to manually trigger (jump) the secondary fuel pump by pulling out the relay and inserting a jumper wire between the 30/87 pins. If the car runs fine, then the primary fuel pump is dead or its electrical supply is at fault.

Along with that guidance, one was cautioned to not jump between other pins as the ECU could be damaged.

So with that caution, I wanted to take extra are and double-check which pins to jump if I used this method while troubleshooting my current issues.

Looking at the location of the secondary fuel relay which is above the battery, I assume it is the same brown relay that is used for the primary fuel pump. I've attached a photo to confirm if that relay location is indeed the relay for the XJR secondary fuel pump. In the photo I have pulled the relay from the socket which I believe is for the secondary fuel pump. If someone can confirm that is the location, that would be helpful.

The other issue is that I can't confirm which pins to jump between. The socket for these brown relays are not labeled 30/87 anywhere, and two of the pins are 12V when the key is on. I have attached a photo of the brown Jaguar relay, and the pins are labeled 1/2 and 3/5 as pairs. It looks like 3/5 would be the pair to jump, but I wanted to see if someone could confirm.

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Some are blue and some are brown as in made in Spain relays on later models . Let me check my research vehicle and will get back .

 

On the # 1 relay the power leg wires are the fwd most and the opposite slot being the aft most . The # 2 is what you have in your pic and is correctly the 3/5 of the relay in hand . I don't have a # 2 but will be doing so later as I reengineering the normally aspirated engine out with higher intake volumes beyond the 165 grams / sec paper isobaric calculation without super charging her requiring a # 2 as a higher fuel volume demand will be required to reach it's potential to match that of the SC engine with the the NA larger crank moment size ( ? ) and the higher original rear end ratio then then then the SC model and maybe going from the her original 3.54 to the 3.77 rear end gears . Vrom , Vrom , did I mention Vrom . I'm just say'in . I can feel it . I digress from the original question , Vrom , Vrom .

Other then a verbal description another way to look at it is the wire colors as can be seen as your pull the relay tray up .

# 1 : Brown / Yellow to the opposite Red / Yellow

# 2 : Brown / Yellow to the opposite Blue / Red

Note the same Brown / Yellow wire as the 2 pumps share fuse # 7 / 30 amp ( green ) in the Trunk fuse box , control fuse that closes the relays is also shared as # 10 / 5 amp RH Heelboard fuse box . The ECU provides a ground to command the relay ( s ) closed .

 

Hi Lady P,

When I grow up I want to be able to create diagrams like you! Those are just awesome!

I assume that's the 1996 schematic? The reason I ask is that the relay terminal numbering changed for the 1997 model year, and the schematics for '97 use the 1-5 terminal numbering consistent with Al's relay:

Jaguar X300 Electrical Guide 1997

Here's the diagram for the SC engine fuel pump relay 2, which confirms Al's suspicion that he can jump terminals 3 and 5 to run the pump:




The same is also true of fuel pump relay 1:



Al, you can bend a large paperclip into a U and jump terminals 3 & 5. When you turn the key to position II (ON/RUN) the pump(s) should run.

Cheers,

Don

 

Thanks to both of you for the very clear response.

So one last question; if this clears up my running problem, can I drive the car with 3/5 jumped and thus the secondary pump running full time with no ill effects until I get the pumps replaced?

..understanding I'd need to keep RPM under 4k since that is when the secondary pump would normally kick in to keep the air/fuel mixture from leaning out.

And if I run it on the secondary pump full time, do I need to keep the primary fuel pump relay pulled, or it is irrelevant whether both pumps may run together if the primary intermittently wakes up?

I assume it is OK for both pumps to run, since that is how it was designed and fuel pressure regulator and injectors handle managing the fuel flow and pressure.


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It's late and my brain is tired, but if the second pump normall only runs above 4K rpm, but you are going to jump it to run constantly, what would happen if you exceeded 4K? The control circuit for the pump relay would close, but the main relay terminals would already be closed via your jumper... Would the ECM have problems for some reason?

If you test this theory, it would be prudent not to use the large paperclip, which could arc in the socket and maybe even fall out while you're driving. Instead, make an actual short jumper wire with maybe at least 16 or 18 gauge wire and spade terminals on each end the same size as those on the relay.

Heading to bed!

Cheers,

Don

 

My Mom says I need to go to bed now . Will review the later posts when I get up in the morning before my Tour - De - Junkyard around Kansas City . Retirement check came in finaly Never work for as a aircraft mechanic for American Airlines , what a waste . Although I got to fix and run some cool stuff .

Updated earlier post

 

Correct on the use of a blade terminal with a short heavy gauge wire , and the battery disconnected so not to arc damage the high current relay power sockets .

The ECU provides a ground for both # 1 and # 2 relay control sockets so by having the relay removed those sockets are open to air . There should be no problem with the ECU unless you jumper the hot wire to the wrong socket and provide unrestricted power to the electronic switches inside the ECU . The relay on the control pulling coils have a resistance that prevents unrestricted power from doing this plus a smaller fuse for the source of power for this half of the relay .

Underfueling with a limited fuel supply as you go beyond the 4000 or so range has been eluding me for a long time as to how does it not go past the EGT limits of the materials metallurgy . It's to complex of a concept to effectively deal with at my level of knowledge . On a piston aircraft you always have a EGT gauge and knob to manually lean or enrich it to a target EGT range as the air gets thinner at altitude .

The both pumps running at the same time at a low fuel demand RPM scenario requires a FPR that can bypass enough volume to keep it down within range . Overfueling can have the result of the unburned fuel bypassing into the crankcase diluting the oil thereby ruining the bearings . With this in mind I would only jumper one pump and leave the other relay removed .

Yes on the 30/87 or 3/5 reference change but the wire colors as the reference if you can see them well enough is the same .

 

You may like to have a read of one of my previous article (attached) regarding fuel pump operation & fitment of a switch to engage pump 2 should pump 1 fail.
Yes a jumper between 3 & 5 (30 & 87) is required however may I suggest you spend 5 minutes & make up a suitable jumper lead as shown in attached photo.
A paper clip etc is a rather crude approach.

John Herbert

 

Thanks for the excellent write-up John. Very much appreciate your documenting that for the community.

Yep I made the identical spade terminated wire this weekend in preparation for this testing.

It's been raining and sleeting here for a couple days, so I haven't had a chance to test yet, but hopefully will in the next day or two... weekend at worst.

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Thank you Lady Penelope, Al & John.

I realize old thread, but my car just died last night!

While I've probably lived through 12 or so fuel pump failures in my life, never had one quite like this.

Car would always start right up again, then stumble & die. Pump could be heard (faintly) running.

So I wasted MUCH time looking everywhere else for problem.

Once I decided to just try secondary pump as a troubleshooting step, I could instantly hear the difference in how the pump should sound.

First time I've had a pump that ran, but not enough. Or something!

But thanks again, all. It's very different having an operable Jag with a known problem safely at home, and a non-operable Jag with an unknown problem stuck in municipal parking lot far from home, right next to a group of 'lively' bars!

 

G'day Gents,

I have a 1995 X305 V12 which sat idle for quite a while and I am in the process of getting everything going again.

Under hard acceleration the car stumbled and misfired a bit making me suspect that the secondary fuel pump was not cutting in.

I checked the two fuel pump relays concerned by plugging them into the horn relay socket and both checked out OK.

Then I thought I'd hot wire each pump through it's individual socket but first I checked to see whether power was available at the socket with the IGN on.There was power available at both sockets. I looked at the information earlier in this thread regarding hot wiring and I had sudden inspiration, why not take the cover off a spare relay and plug it into the pump socket and manually close the contacts? It would save fiddling around with bits of wire here and there. Well it worked like a charm and I could hear both pumps activate and the return flow of fuel back into the tank.

So hopefully by manually activating the secondary pump it will come back to life when it's supposed to.

Now it's time for a test drive.

Cheers,
Jeff.

 

Reference page 35 of the wiring guide the point 104 square ( relay fuse leg ) and carry through to the point 1 square on page 31

The 2 fuel pump relay's power source is hot at all times , so this will drain battery with your key in your hand

 

Jeff you may like to refer to my previous post 3/12/18 and attached article "Spare Fuel Pump"
I note that you live at Twin Waters, Sunshine Coast.
I am at Peregian Springs, basically not far up the road from you.
I have 1996 XJR purchased in 2012 & have compiled a wealth of information on these models.
My Jaguar experience goes back almost 30 yrs & includes XJ Series 3 & XJS. I have always undertaken all mechanical work myself (including wheel alignments) like yourself. My Jaguars have never visited mechanics.
May be interesting to catch up with you sometime, probably a bit more knowledge we are able to share. My email will be sent via Private Message.

John Herbert