I've got a 1998 xj8. It has sit for the last two years before I bought it. I charged the battery up and she cranks over fine but won't start.Code reader won't work, and no fuel pressure.I've checked all my fuses and found the ecm fuse blown changed it and it blew again after I tried to start the car. Don't hear the fuel pumps and was wondering if that was the cause, and if so do both pumps usually go bad ?

 

Welcome to the forum srw676,

I've moved your question from General Tech Help to X308 forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

Since the ECM supplie spower to many circuits, it will take some effort to figure out exactly where the lost current is going. It could be the unit itself, or any of the connections.

One way to troubleshoot a shorted circuit is to connect a resistance in place of the fuse so tyhat the current is limited to a safe value while you test. Assuming you do not have a DC clamp on ammeter (they are $$!), I would suggest installing a 12 volt lamp in the circuit in place of the fuse, then remove connectors (not the one supplying current to the unit!) until the lamp reduces brightness significantly or goes out. Then plug the connector back in and begin isolating each circuit in that connector. It is possible the ecu itself has an internal short to ground, but I would say that is unlikely.

The electrical engineering rule yiou must remember for troubleshooting this is that the current into a node must equal the current out, so whatever is blowing the fuse is also going through another wire (or wires). Find it and you are headed towards done!

Unfortunately it would be nearly impossible to write a step by step due to the complexities of dealing with so many circuits, so I would just say you need to go at it with a schematic and some gut feelings.

BTW, if yoiu want to check your guess- remove the fuel pump supply fuses and see what happens. I doubt that is your root cause since 1) the power source to the pumps is an isolated circuit with it's own fuse, and 2) they will not run with a dead ECM anyway.

Good luck and you will get lots of support if you decide to tackle it yourself.

 

Steven,

Excellent advice from Ross.

The Electrical Schematic is part of JTIS (Jaguar Technical Information System) available as a free download from the forum.

As a newbie you don't yet have sufficient posts to be able to download from the forum so I've put the 1998 XJ Electrical Guide on my MediaFire account. You can download it free from this link:

http://www.mediafire.com/view/2b21ol...ical_Guide.pdf

It's an 8mB PDF.

Graham

 

Thanks a lot guys, I'll get at it this week end get back with you.

 

Great advise from others, a jaguar is far from the F/A-18 hornet I would have to fix but sounds like you need a digital multi meeter for starters to start checking for your short. Eventually another connector with a jumper and a great schematic.

 

Hi srw676,

Great advice from Ross! If you need the Electrical Guide with schematics, I think the link at this forum has been down for awhile, so send me your email address via private message and I'll send you the X308 Electrical Guide in pdf format.

Cheers,

Don

 

Can you tell us specifically which fuse is blowing? There's at least 4 that feed the ECM.

Thanks

 

Its the ECM fuse behind the drivers seat, any info would be great. I'm getting back to it this week, with the info gathered this far. Thanks

 

Can you give us the fuse number and size? Fuses 4 and 6 both are labeled ECM in the book.
Very important- are there any other things that don't work? Anything electrical at all, doors, lights, switches, etc?

I suspect it's #4, a 5 amp fuse. It only goes to the "diagnostic connector" as they call it. I'd get a mirror and a flashlight and check out that connector, even remove it if you can.
I'd also open the compartment where the ECM lives and check the connectors for corrosion. Have a good look around for wiring damage due to mice. If the car's been sitting, you never know. I just found a knock sensor harness chewed through.

 

Well I finally found time to get back at the problem.The fuse is number 4 behind the drivers seat. I also pulled the connector down and found a wire that had been spliced at a previous time (must of had the same problem before)and it didn't look solid so i took the splice off and reconnected the two ends directly. It is a brown and blue wire.Tester lit up when no fuse and no light with fuse. I hooked up my code reader that before i reconnected the wire said that there was a bad link when it got to the end of the scan. Now it got to the end of the scan and blow the fuse. After finding the wire last night and not messing with the bad connection because it was getting dark, it did make a buzzing sound coming from the column when it was manipulated and the battery was dead this morning.I'll be getting back at it tomorrow so any info would be great thanks(got to keep trying! the car only has 30,000 on it)!!

 

It seems all lights work and I didnt see any bad wires in ECM compartment.

 

Sounds like your making headway, Good job.

 

Here's the wire- it goes from the fuse direct to the scanner port, that's all it feeds. It should be a 5 amp fuse. Does it blow without the scanner plugged in?

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The connector CA19 is at the A post, seen here.

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Hello 007, and thanks for responding, I seen that it goes to c 19, but what throws me off is because it says its yellow and the scan connector is black, and the wires appear to run behind the center console and not under the steering wheel where there is two yellow connectors. And no the connector does not have to be hooked to blow the fuse. Maybe its goes to a yellow connector between the fuse and the scan connector under the steering wheel ?

 

Th yellow connector is in the middle of the harness. The OBD port itself is black. I wonder if someone has misconnected some wires, or maybe a wire has chafed against bare metal somewhere.

 

Where the splice was, are both ends of the wire brown/blue? If it's blowing the fuse with no scanner plugged in, then there's a short somewhere.

Go to this address, download the wiring diagrams for your car, then go to Figure 19.1 and Figure 1.2, and check that all the wires are connected to the right place.

https://www.dropbox.com/s/68e9c6xa9jl0gtj/jwj1998en.pdf

 

Ok thanks for the info will get back with you soon. And yes the splice was only about 2" from the connector and both brown and blue. It does look like they were looking for something before (the screws show wear on the console).The previous owners son (owner died)said they had it at a local jag shop and spent like $4000 but didnt know on what? --but started fine for a while then sat .only 30,000 miles on it. o yeah I dont know if it matters but with my lamp tester some of the connectors pins are not as bright as others

 

Well its fixed ! I replaced the fuel pump and filter after finding the grounded wire, I would like to thank all who helped me figure out the issues !! The bad is now I have to sell so anyone interested in a 98 xj8 like new interior with 33,000 miles let me know i'm in the state of Maryland in the US. THANKS AGAIN