Good afternoon.

I am attempting to hire someone to find out why my ECM fuse keeps blowing. He says he will need a wiring schematic to trace the problem. I have the JTIS downloaded, but I cannot seem to located the requested wiring diagram.

Any help would be greatly appreciated. I am on week 5 of this problem and looking to wrap it up.

Thanks!

 

Is this a new problem or was the fuse blowing before sending the module out?


Dave

 

Dave,

I assume that the fuse was the problem. I tested the resistance of the CAN bus and there was no issue there. A local jag expert and I tested every known possibility, however, the owner's manual did not show an ECM/Starter relay fuse in the location where it was found. I found that from a manual that I downloaded on line. Even the JTIS indicated the opposite side of the engine compartment for the fuse. In other words, after five weeks, I thought I had a miracle. When I replaced the fuse, everything came back to life for an instant until that fuse blew. So I cannot your question with any certainty, given the five week nightmare this has been. I was never the ecu, it appears to have been this fuse which caused the ecu to lose power. Now I need someone with the know-how to trace this short or whatever down so I can get back on the road. The guy who has been helping indicates that I need the schematic to trace the fault.

Do you have the wiring diagram?

Thanks Dave.


Madbrad

 

If you open up JTIS click on the button with the odd looking symbol between the service and DTC buttons, then you can select the wiring info you need.

 

Does it still blow the fuse with the ECU disconnected?



Dave

 

Don't thank me, thank Gus !

http://www.jagrepair.com/images/Auto.../jagxk1997.pdf

 

Dave,

I have not tried that, since I reinstalled the ecu.

I just assumed that with the ecu disconnected, it would do nothing. Right now, it only blows the fuse when I try to start the car.

So, disconnect the battery, disconnect the ecu, reconnect the battery and turn the ignition to on, right?

Steve

 

Yes. If it still blows the fuse then its something else that also draws power from that fuse feed. If it only blows when the ECU is hooked up and you know the ECU is good then its likely something the ECU drives such as one of the 2 Ignition Amplifiers (would be my first bet). Then unplug those and see if the fuse still blows.



Dave

 

Thanks again Dave. Anything to do with car wiring is generally beyond my skill set. Given that I know the fuse is blowing, what is the worse case scenario for an expert to track this down in terms of hours?

My biggest issue is that the car will not start or move. I already wasted a month on the ecu, since nothing was wrong. The top won't go up and, even if I manually cranked it up, which I have been warned against, that will leave the rear windows down.

So, flat bedding it once again and taking it to a shop is not in the cards. In other words, I need to find someone to come to the house and work on it in my garage.

I would like to narrow the scope of what needs to be tested, so I appreciate the suggestions. I don't mind spending several hundred dollars to end the nightmare, but it needs to be someone who knows what they are doing.

Thoughts? Hey, wait a minute, why don't you come on up to Richmond!

 

Unfortunately my XK8 is my only car and I don't trust it on trips as the last time I went out of town (to Petersburg) it came back on a flat bed. I haven't gotten around to doing the tensioners yet either even though I have all the parts in hand.
I am looking at a water damaged XK8 thats kind of local to get as a parts car. Or maybe even get it running again and have 2 of the damn things in the hope that both are not always broke at the same time.
On the plus side I may have a buyer for my house after 5 years on the market and if it goes through I will be moving back to Petersburg.
Looking back getting this thing to replace my reliable Alfa after it got totaled was not really a good idea being on disability and broke all the time. I'm just lucky I've been able to keep up with the repairs so far as its my only transportation.
If I could get there I'd be glad to help.
It should be easy to disconnect the ECU (with battery disconnected) and see if the fuse still blows. If it doesn't just unplug the connectors on the Ignition Amps and see if it still happens.


Dave

 

Steve ..........Which fuse is blowing (and in which fuse box) ?
Looks like there are two fuses - #4 @ 5A and #10 @ 5A in the engine management fuse box and #5 @ 10A in the engine compartment fuse box - all three supply power to the ECU but, maybe crucially, also supply power to other things as well.

 

Thanks. It is the latter. #5 @ 10A in the engine compartment -- in my case, the driver's side. Somehow we missed that one. It supports the ECM, fuel injection main relay coil, generator regulator, and starter relay coil.


Any thoughts on how to proceed? Dave suggested unplugging the new tested ECM and see if the fuse still blows.

 

I would also try pulling the injector relay, starter relay, and alternator plug etc as any of them can blow that fuse.

Dave

 

+1 for DaveInVA's suggestion.

I'm no electrician, so what follows is based on guesswork rather than knowledge but ............ if the fuse only blows when you try to start the car, that *might* point to a fault in the starter circuit. I don't think you will do any damage (other than blowing the fuse again) by unplugging the starter relay - that will at least rule in, or out, that part of the circuit from that particular fuse.

Otherwise, unplug all four connections (Pink and White Wires) and just test them for continuity and no short-circuit to ground. Bit tedious, but fairly straightforward with very simple equipment.

 

Thanks to you both. The fuse originally blew while the car was running, which (I think) would point more to the alternator or fuel injection relay. The fuse will blow by going to the on position without going all the way to the start position. I sense it is the alternator, so I will try to find the connector and unplug it. I understand that the alternator is a major pain to replace, but I think I can do that job.

 

If the fuse blows in the "ignition on" position, then I would make a major investment in four new fuses and disconnect each of those four wires in turn to see which one is causing the problem. Pretty easy with the two relays and the alternator connector, more difficult, but not impossible with the ECU plug so leave that 'till last.
Should narrow it down quite a bit with very little effort or cost.

Obviously, there's the possibility that it's more complex than that, but I suggest a reasonable place to start.
Good luck !!

 

Unplugged relays and ecm and still blows the fuse. Ordering the alternator. Hope this works! Thanks for your help!

 

Did you unplug the alternator connector just to be sure?


Dave

 

Not gonna lie to you my friend. I did not. It looks like I have to pull quite a bit off just to see the alternator, so I am taking a (calculated) chance. Plus it would the seem the most logical. By the way, my friend was juggling around some of the relays and I noticed some have different numbers. Just to make sure I get the right ones back in the right place, do know how I can find that reference? I have a chart that identifies the relays, but the not the actual code on the relays.

 

Madbrad.
You may be right - hope so.
But ............. there would appear to be a connector (black 13 way - P12 in wiring diagram) in the engine compartment - pin 12 of this is a "join" in the White / Pink wiring from the fuse to the alternator.
If you can find this connector, you could maybe put a multimeter across the side of the connector that goes to the alternator just to see if there's a short circuit to ground.

All a bit tedious I know, but alternators are not cheap and not easy to get at for replacement.