I have addressed all aspects of this 2001 XKR and it is running beautifully when it is not just stopping dead on the road with an engine failsafe and then crank no start. I have ruled out sooo much and it is impossible to reproduce the issue reliably. May go a day a week or 15 minutes.

my ECU has visible corrosion. My thinking is that this is the smoking gun on the intermittent electrical gremlins and yes, I have a fresh battery and new alternator. I also have a part matched ECU from another 2001 XKR.

What cloning service do you all recommend?

 

You need to get IDS and a Mongoose cable and then you can do the immobiliser setup for the replacement ECU when installed in the car. I don't believe it can be cloned before being fitted. You should also just try the new ECU without doing the setup, as you may be lucky and it will just work as is.

 

Tried the swap, won't fire off which makes sense. Looking around for IDS V131 and a Mongoose cable is getting a little challenging.

 

Using a mongoose or clone runs the risk of damaging the ecu they work for reading ect. But the true VCM should be used for programming. Just a warning

 

My diagnosis is starting to look like potentially an ignition switch? Will run/drive fine and then will stall abruptly as if someone turned the key to ACC. warnings that appear include Engine Failsafe, Gearbox fault and ASC. Even will trigger a "handbrake on" occasionally. Coasting to a stop, I can sometimes refire it right off, other times, I wait and disconnect the battery, and it will ultimately fire off and get me home. Once the stalling starts, I can drive about 2 minutes before it will stall again. When it's cold, I can go up to 10 miles before it will engage.

I'm going to replace the ignition switch next, and see what happens. For what it's worth, iCarSoft doesn't report any issues. No CEL, No Jag codes.

 

For those not so materially invested... replacing the ignition switch didn't resolve problem. But I had the "good" fortune to have it die in my driveway, which meant I could leave it in run mode to do some troubleshooting in fail-state. moving around the drivers' side underhood fuse box resulted in clear changes in items such as power to the injectors, etc. and I had at least a lead on my smoking gun. I have a spare XK8 here so I popped the replacement fuse box in with all good tested relays and fuses.

That was it, guys. 50 miles in and she's zipping. No OBD, No issues.

 

Well done....

 

This is giving me some inspiration. I thought I had made it past the failsafe issues after adding some grounds. After which I drove for months with no issues. Even made a 1000 miles trip without issue. Then the issue came back. I've replaced batteries, alternators, done the cleaning of contacts, etc. I keep a ctek battery maintainer connected when not in use. The issue seems to be somewhat consistent. I will get the issue after running the car and stopping somewhere for 10 minutes or so. If the car is stopped longer (>40min), it doesn't appear to be an issue. Recently with just a short trip, in the store about 15 minutes, when I went to start the car, nothing. Put the scanner on and the ecu and security module didn't show up at all. After a few scanning attempts they did show up and I could reset the CAN faults on the eco, abs and tcm. So there seems to be a heat element and maybe also a voltage element to the faults. The car has been outside this winter, which probably hasn't helped. I've considered replacing the abs as it seems to always have a can error when this occurs. Also, it would be the most likely module to get overheated. I will try to wiggle some cables and see if some issues pop up.

 

If I had to do it all over, the first thing I would have done would be to replace all three exterior fuse assemblies and every relay. They are cheap parts to find used and the 4 pin relays don't have to be OEM Jag and are about a dollar a piece. Take heed of the only 5 pin relays in the boot. Then I would go ahead and get a part matched OEM MAF sensor. Best of luck.

 

If changing relays check whether they are the kind with a suppression (aka flyback) diode. I think the Electrical Guide usually (always?) shows.

 

Yes, absolutely essential. The OEM relays show a drawing of the pinout complete with the flyback resistor on the side of the relay body, as does the electrical guide. I'm guessing the resistor allows the computer to spot if the relay coil has failed.

 

The resistor, by nature, should prevent a lot of the flyback surging that can occur with high amperage relays. And it's funny that comes up... as a preventive measure I just pulled all the cheapo 4 pin and 5 pin relays out of the 2500-dolla (now $13000 dolla) XKR and replaced them with potentiometer-tested OEM brown (4-pin) and black (5-pin) relays from the parts XK8. I can't tell any difference, but that's probably good, right?

 

The DC resistance of the relay coil will likely mask the suppression device - which might be either a diode or, since they aren't polarity-conscious, a varistor.

I've just checked a new Bosch 4-pin, which shows a coil resistance of ~75Ω whichever way the meter leads are connected. Do the cheapo relays carry a drawing on the body?

 

Ha! Seems as if some do, some don't depending on the batch and source. I think I'll stick to OEM/Anco vs a coin flip. Also it seems that "safe" relays can be pulled from any number of very dead BMW/Audi/Mercs that are rotting in everyone's local junkyard.