I need some help figuring out some electrical problems on my 98 XK8.

The car won't start, but the starter is tested as good. I had to replace a Littelfuse Mega 250 fuse in the boot that was blown. I checked and cleaned the grounds in the boot and at the false firewall under the bonnet. I replaced the battery in the key fob. All in the attempt to get the starter to start. There were no fault codes, other than the engine fail safe that is triggered because I replaced the 12v battery with a new one.

Prior to replacing the fuses and key fob battery, the lights and eletrical would work, with the exception of the starter. Now all I get is a red light on the oil gauge and the amp gauge. Nothing else works. I am very confused.

Is this the immobilizer that got triggered, or is it something else?
Is there a way to test the computer? What electrical faults could it be?

I am open to suggestions with much appreciation in advance.

 

Please provide more history. What happened that lead to the megafuse blowing? A 250 amp fuse normally does not blow on its own unless there is some time of incident.

 

Have you checked the inertia switch? Driver-side fuse box that shows when the door is opened wide. It is a relay-looking thing with a push button. Meant to turn everything off in case of a crash. On occasion, it trips and needs to be reset. Just a $0 quick check.

Best of luck, keep us posted.

 

To split the problem in half do you get the starter relay to click ? In the RH enclosure side of the hood .

Do you get engine rotation ?

Yes on the inertia switch check mentioned by Fmertz . It is fical and may not reset so can be jumpered with a paper clip between wire X and Y

 

I bought the car from the previous owner and during their ownership was when the fuse blew. They did not seem to know what the cause of the blown the fuse. They didn't even know there was a blown LittelFuse Mega 250. They just knew the car would not start. The car sat for a few years.

Any other ideas?

 

I could hear the relay(s) clicking when I would try to start the car. The crankshaft does turn manually, so I know the engine turns. There is no voltage at the s-post on the starter when the key in the ignition is set to start.

But now the problem is that the electrical is not working. I only get the two red lights on the oil and amp gauges. (see my original post).

I bought the car from the previous owner and during their ownership was when the fuse blew. They did not seem to know what the cause of the blown the fuse. They didn't even know there was a blown LittelFuse Mega 250. They just knew the car would not start. The car sat for a few years prior to me currently having it.

Further suggestions?

 

Thanks for the info. I had tried some of these prior. I will try them all. My current problem is that the electrical of present only gives me a red light each on the oil and amperes gauges.

Here is a little more information I could hear the relay(s) clicking when I would try to start the car. The crankshaft does turn manually, so I know the engine turns. There is no voltage at the s-post on the starter when the key in the ignition is set to start. That was prior to my current electrical problem. I only get the two red lights on the oil and amp gauges. (see my original post).

I bought the car from the previous owner and during their ownership was when the fuse blew. They did not seem to know what the cause of the blown the fuse. They didn't even know there was a blown LittelFuse Mega 250. They just knew the car would not start. The car sat for a few years prior to me currently having it.

I put a new 12V battery (correct for XK8) in it. Ran a scan for error codes on the scan port. Cleaned and checked all the grounds. Checked fuses, (that was when I found the blown Mega 25 fuse). Plus, I replaced the battery in the key fob. After that was when the electrical problem of present began, (only get red lights on oil and amp gauges on center dash nothing else seems to work).

What would the immobilizer disable? How extensive would the symptoms be? The key turns in the ignition, as it always has since I have had it.

Thanks in advance. I am still scratching my head over this.

 

When you checked the fuses did you also check the small fusebox next to the ECU? That one is under the cover on the right side near the windshield and is often overlooked.

 

Without getting into the items noticed , let's focus on getting the engine running and maybe things will work out after the starting sequence.

The clicking of relays you are hearing is the King relays in the red circles in the pic in the corner of the fuse boxes . You should put your finger on the specific starter relay and feel for that one . If it does click doesn't mean the relay is good and can be swapped . If it doesn't click swap out and try again .

Once you get it started we'll work out from there to remedy your electrical system as a whole .

You must have 11.5 volts for the ECU to start the engine .

You may have put the engine in a bore wash condition and don't have the compression for a light off . Easy to remedy

Let's get the starter to rotate the engine first .

 

Thank you for your excellent instructions and diagrams. This includes the one from a previous thread on no start problems where you outlined the "constant power and key power" with red lines. I had intermittent no start problems for several months. With the help of your instructions and great diagrams, I was able to locate, remove and reinsert the starter relay and what do you know, it now starts. Taking no chances I ordered a new starter relay for less than $10.

 

I pulled the relays and applied 12v to the prongs (1 and 2 on the relay) to close the loop and tested the continuity between 3 and 5. The relays click audibly, and the continuity is good on all.

I am familiar with cylinder wash. There is no cylinder bore wash, as the starter is unable to turn the engine at the moment, since there is no power on it. The starter has been pulled and tested good.

This appears to be an electrical issue, since the only lights to come on are the red light on the oil gauge and amp meter. I just wasn't sure if it is an ECM/ECU or immobilizer issue. Any suggestions are welcome. TY