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Year 2000 XK8 fuel pressure problems. In trunk fuse box, fuse 7 is ok.  Relay 4 is ok. Contact 1 on Relay 4 gets 12volts with ignition ON. Relay 4 does not Activate. The relay 4 contact 2 seems to be to earth so what is inhibiting the relay 4 pull in?

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Hi

looking at the wiring diagram, relay 4 has a ignition feed to it but the earth to the relay is switched through the engine ecu

so its engine ecu holding it off

dont know wether you have wiring diagrams but look here http://www.jagrepair.com/

wiring foe yours http://www.jagrepair.com/images/AutoRepairPhotos/jagxk2000.pdf

cheers

Joe

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Thanks Joe. I suspected that relay 4 was earth switched via the ECU but without a wiring diagram was shooting in the dark. My starting problem began after I interrogated the ECU for a fault code after engine misfire. It indicated an ignition coil problem. I reset the codes and the engine would not start. (no fuel pressure at the manifold). I tried an ECU hard reset by disconnecting the battery but this did not fix the problem. Any suggestions?

Les

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Hi

You need to plug in with jaguar software really

sounds like some immobiliser fault, or a fault on a module

ive seen it on rare occasions where, plugging in fault readers or disconnecting them at the wrong time can cause faults

only way to know for sure if you can get it plugged in

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Thanks Joe,

I assume that another battery disconnection will not give a clean upload or reconfigure ? Do you know what software configuration we are looking for and does it need a Jaguar expert of will an auto electrician be good enough?

Thanks for the Electrical drawings. At least the hardware makes sense now.

Les

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hi

the software I use is Jaguar IDS/SDD with a Mongoose lead, there generally about £100

but your most probably better getting a local Jaguar independent garage have a look

do you get any warning messages

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Hi Joe,

Thanks for the advise on the software you use. Obviously the Jaguar team should know what to look for but the closest dealer is probably 15 miles away and the car wont start.

There are no warning lights and the pre start checks with all of the warning lights going through their cycle looks normal. I will check again to see if there are any codes present.

In the worse case scenario what is the availability / cost of a second hand ECU?

I will chase up your immobiliser theory.

Les

 

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Hi Joe,

I have done another hard reset by battery disconnection. After reconnect I crank engine to no avail and then check codes. The Fault code coming up is P1230 which I think is fuel pump relay. Freeze frame is P1230 and Fuel system 1 O/L and ETC 75. So it is telling me what I already know that Relay 4 is not pulling in. I have exchanged Relay 4 with another and no change. I have put 12volts across pins 1 and 2 and the relay clicks ok  The relay pin 1 voltage changes state with ignition ON/OFF. The relay pin2 is always at earth with ignition ON/OFF but I think that with Ignition OFF it may be due to the ECU current sensing circuit (high impedance)??  I think you told me that the ECU switches the relay to a low impedance earth.

So for some reason the ECU is not switching the fuel pump relay.

Les

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Hi team

I have found something significant at last. I checked all the fuses in the ECU fuse box and found a 10amp fuse blown. I replaced it and went for engine start. There was a smell of fuel which is encouraging but engine did not fire. I checked the fuse again in the ECU fuse box and the same 10 amp fuse has blown. I replaced again and no problem with ignition OFF. When I put the ignition to ON (not cranking) the fuse blows again. 

I am trying to identify what the fuse does but cant find a fuse box layout. The fuse in question is the 10amp at the farthest end from the relay (and on the same side).

Any ideas?

Les

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Ok I have found that it is fuse 18 in the ECM fuse box. The electrical drawings show that this provides power to the Ignition relay which in turn powers all of the spark plug coils.The fact that the first OBD code that was displayed related to No1 coil I checked it and found that pins 1 to 4 were short circuit and the reason for tripping the Fuse 18. It is also the same supply which provides the ECM inhibits to the Fuel supply by preventing relay 4 (fuel pump drive) from engaging. This makes sense as if there are no sparks then no point in spraying fuel.

So in a nutshell I was very unfortunate that the No 1 coil failed in a short circuit to earth mode and made it look as if I had a fuel pump problem. Luckily I took all of the right decisions with the help of Joe providing the electrical drawings and suggesting an ECM inhibit issue.

Thanks Joe. I want this info to be captured and help others not to fall into the expensive Fuel pump change when it was only the cost of a new coil.

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So to recap. If no fuel pressure at manifold check Fuse 7 in trunk fuse box. Then check relay 4 in trunk fuse box (clicks when ignition turned ON).  If relay 4 does not click then finally check fuse 18 (10amp) in EMS fuse box. If fuse 18 blown then check if the OBD codes suggest an ignition coil failure. If all ok then jump pins 3 to 5 at relay 4 and pump should run. If does not run change fuel pump.

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