On the drive home from work, my 1990 Jaguar XJ6 Sovereign was running perfectly; no problems at all. When I arrived at the house, I put her in the garage and went inside. About 10 minutes later, I decided I needed to run an errand, so I went out to the car, put the key in, and tried to start her. She turned over, the engine caught and surged a little, and died. I tried again and she turned over, but wouldn't start. A couple of other attempts resulted in the engine starting, barely, surging, and dying.
I consulted the VCM and it was displaying a fail code 24. Looking that up in my Haynes manual revealed that this is an "ignition amplifier circuit" failure. Has anyone experienced this, and what do I need to do?

 

I had a customer car that had a 'no start' fault (1990XJ6) due to a circuit fault with the ignition amp (no power to the amp). I found a harness connector under the glove/cubby with a burnt contact (white/red or white pink wire). The connector provides power to the amp. I cleaned the contact and the engine started. A few months later he called and said it would not start again so I told him exactly what to look for. He found it and placed a jumper around the connector for that wire and it has been good for several years.

Publication S91 has wiring diagrams and test procedures for 1990 to 1994 MY XJ40. The .pdf is almost 14MB so it will not upload to this site.

bob gauff

 

@Bob, Hi, if you want to send it to me for inclusion, feel free. LOL

 

AJ6 4.0L Engine Management Systems Diagnostics Guide now included. (thanks Bob)

 

Well, I had a quick opportunity to check out the Jaguar. I pulled the coil wire out of the distributor and had my wife turn the engine over. There was spark from the coil wire to ground, which would indicate to me that the ignition module is good. Tomorrow, I will attempt to find time to check for spark at the spark plug wires to eliminate the distributor as a problem area. Does anyone know how to check the spark plug wires for a spark? There is at least 1/2 to 3/4 inch of rubber between the metal connector on the plug end and the spark won't jump that distance, I don't think.

 

Just plug in a sparking plug and lay it on a good earth point (ground), crank and watch for spark!!!
You can also clamp a large ground wire to the plug to ensure an earth for the circuit.

bob gauff

 

Thanks, Bob. I did as you suggested and I AM getting power to the plugs. Next, I disconnected the fuel line at the fuel rail and turned on the power. No fuel was pumping. So I either have a bad fuel pump, or a bad relay. I'm checking on the relay now. Is it possible that there is anything else? I looked at the schematic and didn't see a related fuse. Any thoughts?

 

One question, and I know someone out there has the answer. How do I know which is the fuel pump relay? I removed the right side padded outer panel, and the inner metal panel to expose a row of relays. There must be twelve relays under there. Some are way up inside the dash. Looks like I might have to remove a panel to get to them. But how do I know which relay is the fuel pump relay? I tried to check the wires against the wiring schematic, but couldn't match any up.

 

There is usually a diagram stuck to the metal panel with info to each relay (base connector color and relay color) If the placard is missing then a wire color identification is required to confirm the correct relay. Brown and Blue/Red are the power wires in/out. White/Brown and Pink/Brown are the relay coil power wires.

good luck

bob gauff

 

Thanks again, Bob. Don't know how I missed that diagram. According to the diagram, there are six in a row that are not related to the fuel pump. Below those six, there are two that are identified as the "PI PUMP" (red connector) and "PI MAIN" (yellow connector). The wires leading to these two relays don't seem to correspond to the description you gave. Specifically, the pink/brown wire.
Further up inside the dash, there are at least two relays that I can see. If you look at the close up of the two relays, you can see a purple connector to the left of the red one. It's too tight to determine what color the wires are. Could one of these be the fuel pump relay, and if so, how would I get to it?
I thought it would be easier to check the relay first, but maybe I just need to jack up the car and see if there is power going to the pump.

 

This morning, I jacked up the car and with power on, I connected a test light between the terminal on the fuel pump and the chassis. The test light did not illuminate. So I assume that there is no power getting to the pump. Is that a correct assumption? I also tested what I believe is the fuel pump relay. It seems to be okay. I ran a wire from the positive post of the battery to pin 85 and from pin 86 to the negative post of the battery. The relay clicked, so I am assuming that it is good. What else could be the problem?

 

Further developments: A little while ago, I thought I would try switching the fuel pump relay for another known-good relay. I did so and still there is no power to the fuel pump. I am assuming that the fuel pump ground is through the contact of the fuel pump with the frame member of the car, so there wouldn't be any broken ground wire to look for. What about a connector? Does anyone know where there is a connector for the fuel pump that I can check for corroded contacts, etc.? I'm just clutching at straws here, because I can't figure out what the problem is.

 

The weirdest thing just happened. After playing around with this problem for the past 6 days, contacted the owner of Jaguar Services of Tulsa. He told me that I needed to have someone turn the engine over while I checked for power to the fuel pump. So I got into position under the car and had my wife turn the engine over while I checked for power to the pump. As soon as she turned the engine over, the pump started buzzing and the engine started right up. All I can figure is that there was a connection somewhere that I jiggled while troubleshooting and it's running fine. Go figure!

 

I spoke too soon. Now I'm wondering if maybe the fuel pump ground is bad, because the pump started running when I connected the trouble light to it and had my wife turn the motor over. Anyone know where the fuel pump ground is?

 

I'm starting a new thread on this problem as it isn't related to the original fault code. Hope that is okay.