Four or five times a year, twice after being in a car wash, I turn the key, the dash lights up but the starter doesn't kick in. I twist the key again, most times it starts, but a few times, and last week, I tried to start it for about 4 minutes before it suddenly started. Have a new battery, new exciter ring, changed keys, new starter relays, still does this. Dealer finds no computer codes to indicate anything wrong. Never does this when in the shop, of course. Any ideas?

 

There are two large power fuses in the boot behind the spare tire. Make sure the bolts on these are clean and tight (disconnect the battery first before putting a wrench on these).

Make sure there is no corrosion on the battery cables, especially at the wire crimp.

Also check each fusebox and make sure all the relays are firmly seated.

 

thank you for your suggestion. Question - since the dash lights come on when this occurs, doesn't that mean that power is coming from the battery, just not to the starter? Would that rule out the battery cable corrosion concern? I will certainly look at everything you have suggested but am trying to understand the electrical pathway involved in this problem as well. This problem has been occurring off and on for almost 4 years and it is getting tiresome. I'm determined to get to the bottom of this even though my dealer has thrown in the towel.

 

A corroded conenction that can pass a few amps for lights without a problem can cause a large voltage drop (read failure) where 100's of amps are demanded for a starter.

I listed some of the things other members have run into with internittent electrical problems on XK8s. It is by no means comprehensive. Check these out, and if these are not successful, let us know and we'll come up with some more things to check.

Intermittent problems can challenge your patience.

 

As WhiteXKR says intermittant faults are a complete PITA.

You need a logical chain of checks, when the problem occurs do you hear any clicks from under the hood when you turn the key?

If so the easiest thing to start with is to measure for voltage at the starter motor.
It could be the starter motor that has failed. There are internal relay contacts that can fail, kits are available to fix that problem.

But you need to isolate where the problem is first, hopefully the attached electrical diagram will help you.

http://www.captainjaguarscathouse.com/Electrical_Guides/XK8 2004 Elec Guide.pdf

 

If you open both car doors, there are plastic covers over recesses on the sides of the dashboard. The fuseboxes inside are grounded/bolted to the frame. Be sure those are tight and not building up excess heat. One of mine was loose once and gave me intermittent starting problems.

 

I'm having the same symptoms that started in July. About once in a dozen starts, it will do something weird, but so far always starts on the second try. Never misbehaves when I've got gauges or instruments hooked up in effort to isolate the problem. Tuesday, I even got the dreaded "gearbox fault" message. Had it towed home, but next morning I tried to move the car in the driveway and it seemed fine and there were no codes logged. I'm not going to drive it tho till I can get the transmission checked out. But in researching I read over on a LandRover forum, they have documented situations of getting the "gearbox fault" message just from a low voltage problem. I may have two separate issues, but mabe not. Good luck. I'm subscribing to this thread to follow your progress in case it helps me.

 

Here's the power distribution.
You can see the starter is independent of the rest of the electrics.
I believe the 'false bulkhead stud connector' can be a baddie.

 

Thanks for all the suggestions. So far I have found no evidence of corrosion, all fuses so far seem to be firmly seated, but I have several more to check out, thanks for the power diagrams. Haven't located the high power protection modules yet but will do so this weekend. Not sure where to find the false bulkhead stud connector or even what it is. Lots of reading to do. I'm optimistic that eventually the culprit will be located with all of this assistance.

 

Replace your starter. I went through that for about 6 months -- never knowing when it would kick over or not. The starter had a dead spot in it. I didn't go for the expensive new one, but I did get a dead one on the first try from a wrecking yard. You can go online and find used ones that tell you the mileage of the vehicle removed from, though.

Or, you can have it rebuilt if it can be. I have one frozen one and my original with its glitch sitting in my garage. Good door stops until other owners need a rebuildable unit.

I see you have an '06 with probably not a lot of miles. Your starter shouldn't have gone bad, but if you're close to the ocean where the car sits it could die early. SO...get a good ammeter and take a reading when you are trying to crank it. If it pulls excessive amps it will be the starter. You can try adding voltage to the system when cranking to see if it changes anything. Does the starter make any noise when you hit the ign? A click? A 1/4 turn? Anything that says it's trying to turn?