In-tank fuel pump electrical connector

Hi All.

Engine died while driving, had the car towed home. There are no engine codes.

I just started troubleshooting and have performed the following steps:

1. Fuel pressure? Disconnected the fuel rail and cranked the engine. There is zero fuel pressure.
2. Fuel pump running? Listened for the in-tank pump running while cranking the engine. No sounds detected.
3. Is the inertia switch working? On this model year, it's on the driver's side on the foot well. Checked and reset. Switch is working fine.
4. Is the fuel pump relay working? On this year model, it's located in the engine compartment, on the left side of the vehicle by the brake booster. Can't miss it; it is labeled "FUEL PUMP" in big letters. Checked continuity when open and closed. When the key is turned to ignition, the relay closes for about two seconds, then opens. Seems to be working fine.
5. Is there electrical power to fuel pump? Removed the padding around the fuel tank in the trunk and disconnected the electrical harness that goes to the top of the in-tank fuel pump. There are two wires that are part of this connector going to the pump. The volt meter registers some voltage while cranking the engine, but this voltage is much lower than I would expect.

My question is why is there such low voltage (about .006 volts) going to the fuel pump? What is the expected voltage needed for the pump to work?

Thanks.

1992 Jaguar Vanden Plas 4.0 liter.

 

Put a 'jumper-wire' in the rely socket and leave the ignition key alone.
The fuel pump relay is next to the brake booster in the engine compartment.

bob

 

Just so that I'm clear and don't end up causing a short.

The relay has 4 wires. Two thicker wires that activate the relay and the other two are the circuit that (I think) goes to the pump, normally open, but closed when the relay activates.

I will place the "jumper-wire" on these last two. When you say "leave the ignition key alone", should the ignition be off, but with battery connected?

What am I looking for here?

Thanks.

 

You need to 'jumper' the 30/87 terminals. (Sometimes marked 3 and 5)
The key does not need to be on because there should be power to the 30 terminal at all times (battery connected).

The 87 terminal is the power to the pump.

bob

 

Dumb question:

If the power is on at that terminal at all times, wouldn't that keep the fuel pump on at all times?

 

What turns the relay coil on??The ECM!!!!!!!!!!!!!!!
The 30/87 cannot contact unless the 85/86 coil is energized. This is how relays work.
Electromagnetic energy commands the 30/87 contacts closed. The power flows to the fuel pump.
The 30 power is disconnected unless the contact is made to the 87 so it does not matter if power is constant or switched also. (redundant)

I guess you could 'failsafe' the power so that the 30 power is switched on AND the relay is closed at the same time. This would add complexity to the circuit but ensure that the 30 power is disconnected as well as the 30/87 relay power.

What would you do to disconnect the 30 power, a switch or another relay? A series of switches and relays will ensure that the power is connected/disconnected by more than one circuit.

I think that the design is sufficient.

bob

 

I jumped the relay labeled "fuel pump" as you suggested, but there is still no voltage going to the wire harness pictured in my first post. I did this with the ignition turned off and turned on. Same results.

I don't see any markings 30/87 on the relay, but I'm sure I selected the right two connectors.

Is this the only power source (electrical connector) that goes to the fuel pump? Since the top of the pump is well showed into the trunk, could there be another power source (connector) I'm not seeing?

I hesitate to apply direct power from the battery to this connector for fear of damaging the pump.

Thanks.

 

Hi Palmero,

Sorry for the late reply but I've been traveling and have just now had a chance to study your problem.

First of all, the schematic for the fuel pump circuit can be found on pdf page 71 of the Electrical Guide, which you can download here:

Jaguar XJ40 Electrical Guide 1991-1992

Just a quick review of the schematic shows that power for the control side of the Fuel Pump Relay comes via the Main Relay on the White wire with Brown tracer line (color code WN). The control side is grounded by the ECM via the Pink/Brown wire (KN). Power to the load (fuel pump) side of the relay arrives via the Brown/Black wire (NB) from fuse C8 (25A) in the left A-pillar fuse box. When the relay contacts close, power travels to the fuel pump and to the oxygen sensor heater via the Purple/Red wires (UR). The fuel pump is grounded at a stud on the left side of the trunk behind the carpeted trim panel. Checking fuse C8 would be a good next step.

The connector to the pump module on top of the fuel tank has been known to deteriorate or burn from arcing. You can cut a slit in the sound insulating pad on either side of the evaporative flange on the top center of the tank, fold up the flap and get a flashlight up in there to inspect the connector. If you can't see the connector in situ, you may be able to reach one hand in there and disconnect the connector so you can carefully withdraw it and inspect it.

A suppresion resistor is wired in parallel across the motor terminals. I'm not sure where this is on a '92, but on our '93 a diode and capacitor were wired across the fuel pump harness wires near the connector on the top of the fuel tank and one of them shorted, blowing the fuel pump fuse. I was able to deduce or guess their values and replace them.

One basic test of the motor would be to check it for continuity/resistance through its windings. On your '92 this is complicated by that fact that there is no convenient harness connector between the relay socket and the pump at which to measure the motor, and also by the fact that the same Purple/Red wire that powers the fuel pump also powers the O2S heater, so measuring resistance between the relay socket and ground measures both the motor and heater, which will probably be of no diagnostic use. One idea would be to disconnect the oxygen sensor harness connector (on our '93 this was clipped to the engine oil dipstick bracket). Then measure the resistance between the Purple/Red wire at the fuel pump relay socket and a good chassis ground, such as the battery negative cable. I would expect a resistance between a few tens of ohms and maybe a few hundred ohms, but not zero and not infinity. Zero ohms might indicate a shorted harness. A very low resistance greater than zero might indicate a shorted motor winding. Infinite resistance might indicate a broken harness or motor winding.

It's late and I've got to get up early but I'll try to think of additional ideas. Please keep us informed.

Cheers,

Don

 

I applied power directly to the fuel pump and heard it running. My problem is definitely electrical. Fuel pump is not getting enough juice.

I will follow your suggestions and the electrical diagram tomorrow to see what I can find. I find it strange that there are no codes or any faults in the dash. I would expect a fault code like FUEL 22 if it was the circuit.

Really appreciate all the responses and suggestions.

 

OK, thanks.

 

Hi Palermo,

The On Board Diagnostics I system is quite primitive and will give us no clue for many malfunctions, including ones that will cause no-start conditions.

Please keep us informed.

Cheers,

Don

 

PROBLEM SOLVED!!!

Before I let you know what I found, I'd like to mention that although I'm not a professional auto mechanic, I've been working on cars for many decades now. I purchased this Jaguar brand new, and have done a lot of work on it over the years. Besides regular maintenance like oil, transmission, and differential fluid changes, I've replaced the fuel pump once, done several brake jobs, replaced water pump, belts, most smog components; EGR valve, throttle POT, oxygen sensors, shocks, valve cover gasket, etc., etc. Just about everything short of engine or transmission overhaul. Although I feel confident doing an engine overhaul, I would not tackle major transmission repairs.

I agree that the dashboard codes do not provide all information, but in the past they have served to get me started. For example, a while back I was getting a Fuel 17 code. This helped zero in on the throttle POT. Dash lights also help determine if there is a burnt out bulb or fuse. In this case, there were no fault codes, no dash lights indicating a burnt fuse, or any other indicators as to what may be wrong.

After many hours of work and much head banging on my garage door, I found the problem (drum roll please.... )

As I mentioned in my earlier post, one confusing factor was that I was able to determine continuity from the fuel relay to the pump wire harness in the trunk. In fact, there was residual voltage that varied when the engine was cranked. However, this voltage was insufficient to get the pump going. I connected a variable DC power supply directly to the pump and as I cranked up the output, I could hear the pump working.

I then decided to do a comprehensive check of all fuses, specially the 25-amp fuse mentioned by Don B. that's located at C-8 on the driver's (left) side fuse box. This fuse is clearly labeled "Fuel Pump Control Lambda Sensor". On visual inspection, the plastic was cloudy, but I could see some dark (burnt) marks inside. The minute I removed it, I got the Fuel 22 fault code and the burnt fuse light. After putting in a new one and clearing the fault code, the car started right away.

I then tested the "burnt out" fuse with an ohm meter, and it still had very low continuity. I have never come across a fuse that's burnt, but not quite all the way. I am guessing some of the residual carbon was bridging the fusible link and letting enough voltage through to "fool" the on-board diagnostics, but not enough to run the pump.

I should have kept Occam's razor principle in mind and checked the fuses first. Lesson re-learned.

Many thanks to everyone who posted great advice and suggestions. I hope this post helps someone in the future.

 

The pump seems be drawing too much current so I would replace the fuel filter if it has not been done lately.
Could also be a dying pump?

Glad you got it sorted.

bob

 

Yes, the question is “why did the fuse blow out ito begin with?” The pump was replaced about 10 years back, and has about 50k miles on it, so it could be time again.

i did replace the fuel filter.

thanks

 

I have rewire the fuel pump all the way to the relay. Still won't run by it's self with jumping the fuel pump. I'm thinking I burnt out the oxygen relay by jumping the relay.???? The car will run rough and back fire and won't hold idal.?? When I increased the fuel paddle it will run fine then run rough after that.???

 

Beware of the 'crappy-blue-HELLA-relays'.

 

I've done most of what you pointed out. The brown/ yellow wire coming from the fuse box is live, l get that part. But when it hits the relay it doesn't send power over to the blue/red wire?? To power the pump??. Does it have to do with the oxygen relay if I some how shortened it out by jumping the fuel relay???

 

Could I've have shorted the ECM out by jumping the fuel pump?? The pump works great but not by jumping it??

 

Hi David,

The fuel pump relay is not connected directly to the ECM, so it is unlikely that you shorted the ECM by jumping terminals 30 and 87 in the fuel pump relay socket. Have you tested the fuel pump relay and O2S relay? Easy to do with a 9-volt battery and a voltmeter.

Here is a diagnostic procedure by Bryan N at the Jag-Lovers forum that has always worked for me when I've needed it:

XJ40 - ‘93 / ‘94 Fuel Pump Circuit Test Procedure - Issue 2
[Assuming that you have dash lights with the ignition 'ON']

1) With ignition OFF
2) Remove fuel pump relay (black base, right rear corner
trunk above BFM)
3) Do you get 12 volts at pin 30 (Brown/yellow) of the fuel
pump relay base from fuse C6 in right fuse box?
4) If yes, jump pin 30 (Brown/yellow) and pin 87 (Blue/red)
in fuel pump relay base - does the pump run continuously?
5) If pump does not run, fault is in the wiring / connector
between fuel pump relay and pump
6) If pump runs, suspect fuel pump relay is defective.
7) Replace / re-fit fuel pump relay
8) Remove oxy sensor heater relay (yellow base on firewall)
9) Do you get 12 volts at pin 30 (Brown/pink) of the oxy
sensor heater relay base from fuse C4 in right fuse box?
10) If yes, jump pin 30 (Brown/pink) and pin 87
(Blue/purple) in oxy sensor heater relay base - does the
pump run continuously?
11) If pump runs, suspect oxy sensor heater relay is defective
12) Replace / refit oxy sensor heater relay
13) Remove EMS main relay (black base on firewall)
14) Do you get 12 volts at pin 30 (Brown/yellow) of the EMS
main relay base from fuse C1 in the left fuse box?
15) If yes, jump pin 30 (Brown/yellow) and pin 87
(White/brown) in EMS main relay base
16) Try this both with the ignition ON and the ignition OFF
17) Do you hear the fuel pump give its half-second priming
burst? [You can repeat this many times and you (or an
assistant listening at the open filler neck) should hear the
half-second 'whirr' of the pump every time you jump pins
30 and 87 of the EMS Main relay base]
18) If yes, suspect the EMS main relay OR the EMS ECU is
defective (the latter, very unlikely but possible)
19) Turn ignition OFF
20) Replace / re-fit EMS main relay
21) Remove Ignition 'ON' relay (on a '94 it should be in a
white base on the firewall but on a '93 it may be buried
under the dash behind the radio)
22) Do you have battery voltage at pin 30 (Brown) of the
Ignition 'ON' relay base?
23) If yes, temporarily jump pin 30 (Brown) and pin 87
(White/pink) in the Ignition 'ON' relay base
24) Do you hear the half-second priming burst from the pump
each time you jump those pins in the Ignition 'ON' relay base?
25) If yes, suspect the Ignition 'ON' relay is defective or
fuse A5 (fuse A3 on ‘94 models) in the left side fuse box -
but if either is defective, you will get NO dash lights when
you turn on the ignition.
26) If when you jump pins 30 and 87 of the Ignition ‘ON’
relay base you do get dash lights but you do not hear the
half-second priming burst from the fuel pump suspect the EMS
Main relay.

Cheers,

Don

 

No I haven't gotten that far get. But you just gave me some hope here. I have that lightning bolt light on when the car is trying to run? I did some tamping with that purge valve? But I did take it off and hot wire it to see if it works and it does. Why do I have a air hose missing off that valve? It has 2 air **** from it but one is going to the manifold but the one is missing? Where do I find that one and where does it go?
I love to keep this car if I can understand it better. The car has been running rough and some back firing . It's been running in limp mode since this fuel pump problem I talk about in my last Post .