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I wanted to update this topic and all related topics I created. I had a “no start” condition with just clicking, no cranking. You would have to wait and try again one or four more times and the car eventually started right up. If you did it too soon it would come up with gear box errors, so you had to give it a moment and try again. This happened sometimes daily, but at best every couple of days…..This was accompanied by really scary sudden death situation, where the car would just die while going at random speeds anywhere. Wipers would go on and of, the climate control and radio would reset as if someone had literally disconnected the battery while driving at 40 miles per hour down the road… and you would get all sorts of gearbox error messages as well…..and then start right up…. I think I am willing to say now with certainty that the culprit to all this was the forward engine fuse box, which in the 2005 models , contains a “non serviceable” starter relay within it. I found one topic here and a couple on the interwebs that made me decide to try a fuse box.
-I replaced the fuel pump 4 times
(yes that’s correct) - the first three with just the pump element - and the fourth one I just ordered the whole part from Jaguar Classic parts in the UK because I broke the level sender on the third attempt.
-I replaced the throttle body with a Jaguar Classic parts part
-CPS with Motorcraft part
- ignition switch Motorcraft part
- starter, ( now that the car starts every time I am finding that replacement starter whirls every 30th or so start attempt so gotta replace that again)
- all serviceable relays
-Batteries that were perfectly fine thinking they had failed.
-ignition barrel (but I never installed it TBH)
-all new coils (with 95k miles on it that’s just maintenance to be fair, but I never had a misfire)
I am pretty sure a lot more stuff got replaced with new stuff that I can’t even remember. All new , genuine stuff.
I was very lucky enough to find a brand new harness that came with a new fuse box from a seller in the UK. I just replaced the fuse box and the main power cable that goes directly to the battery. Not the rest of the harness.
Now my concern is A) how did the fuse box die and B) are the fuse boxes repairable….
This particular issue (as well as other personal things going on) almost landed my car in a junk yard. I kind of stopped fixing it anything else on it and figured I would just replace it when it no longer started at all or the car would eventually kill me dying randomly on the highway. I recently decided I liked the car too much to let that happen so I started furiously throwing new parts at it again.
Now , knowing what the problem was , it makes me want to figure out what caused it, how to prevent it and how to solve it in the future for myself and others.
I can’t find anyone online who can service these fuse boxes….any ideas? Or any ideas on how it died to begin with? The problems started when I opened this topic in 2021 when the car had 83k miles. It’s now 2024 and I have 95k miles. It literally took 3 years and 12k miles to figure out
That is a lot of new parts! Glad you got it sorted. There are only 2 things I see that could go bad with the fuse box. As you mention there are 2 non serviceable relays, the likely culprit is R13 slave ignition relay. The other non serviceable relay is for the starter so wouldn't explain the engine suddenly dying. Probably. If you are curious you could bench test that relay but you aren't likely to find a smoking gun since you mentioned it is intermittent. Out of the car with no heat and no engine vibration and no power running through it, it probably works every time. The other thing that could go bad is just a poor connection. Connector not fully seated vibrated out after 18 years, wire to pin crimp is failing, corroded connectors, etc. By replacing the fuse box you wiggled that connector back in place or scraped a little corrosion off a pin. Not satisfying but it could be that you fixed it just by pulling all the connectors off the fuse box and putting them back on.
I don't understand the slave ignition relay. I thought the point of an ignition relay was to use little wires and little current through the ignition switch and switch the bigger load needing fatter wires down by the battery. Now the relays need relays?
That is a lot of new parts! Glad you got it sorted. There are only 2 things I see that could go bad with the fuse box. As you mention there are 2 non serviceable relays, the likely culprit is R13 slave ignition relay. The other non serviceable relay is for the starter so wouldn't explain the engine suddenly dying. Probably. If you are curious you could bench test that relay but you aren't likely to find a smoking gun since you mentioned it is intermittent. Out of the car with no heat and no engine vibration and no power running through it, it probably works every time. The other thing that could go bad is just a poor connection. Connector not fully seated vibrated out after 18 years, wire to pin crimp is failing, corroded connectors, etc. By replacing the fuse box you wiggled that connector back in place or scraped a little corrosion off a pin. Not satisfying but it could be that you fixed it just by pulling all the connectors off the fuse box and putting them back on.
I don't understand the slave ignition relay. I thought the point of an ignition relay was to use little wires and little current through the ignition switch and switch the bigger load needing fatter wires down by the battery. Now the relays need relays?
well it could be that main power cable that hooks up from that fuse box directly to the positive battery post. I made sure I replaced that with the new one that came with the brand new fuse box. Nothing seemed loose or improperly seated, as a matter of fact it was a bit of task disconnecting everything, it was pretty secure in there. But the main power cable failing makes sense even in what happened when the car spontaneously died at speed: .the windshield wipers would **always** come on and of as the car was dying…..relay R4 is in fact, the windshield wiper relay, so the whole box was loosing power somehow. These problems (the no start and the random dying) would happen in the mornings, afternoons and just so randomly and repeatedly that it never occurred to me that it could be that cable. I guess I always assumed a battery cable that’s failed in that way won’t have problems early in the morning, only when the car is hot……I think I am going to see how to test that cable, because it will give me lots of peace of mind to know that the box did not fail due to either poor build quality or something I did incorrectly while disconnecting or reconnecting my batteries etc .
There is a nice write-up on some BMW forum that google and I can't find just now about these hot battery cables. The problem isn't so simple that the resistance of the cable goes up any measurable amount. The individual wires get corroded at the battery end. The area of clean copper contact from individual strands decreases and causes smaller and smaller patches for the electricity to flow. The current remains the same but the current density goes up in small local areas. A lot of current in a small area heats up. The heat increases the rate of corrosion so the problem continues to get worse with time. That was the theory, anyway. They had microscope pictures and some electrical test equipment, it seemed legit.
Spike, if you want to test that cable, there is only 1 way I can think of and that is to send power through it. Lots of amps. I would say that if you have a welder, that would be ideal. You would simply connect that power cable between the ground point and the ground clamp. then do a heavy weld where you are pulling 60+amps through the wire. From there, having a FLIR camera will tell you all the details you will want. Where the cable has even a slight higher resistance, you are going ot see the cable be warmer in that spot. But, odds are, the connectors were probably the source of the problem. But, you should see a connector that is having a resistance issue turn brown from the heat. Kinda like if you have a wire failing under the insulation, this will normally cause the insulation to discolor. It doesn't need to be much. You get a simply 0.1 ohm change and you run say 50 amps through that wire, that is a 5 Volt drop and a 250 watt heat source (think about how how a 60W incandescent bulb gets, now put 4 of them together). the voltage drop would definitely raise hell with the car.
Spike, if you want to test that cable, there is only 1 way I can think of and that is to send power through it. Lots of amps. I would say that if you have a welder, that would be ideal. You would simply connect that power cable between the ground point and the ground clamp. then do a heavy weld where you are pulling 60+amps through the wire. From there, having a FLIR camera will tell you all the details you will want. Where the cable has even a slight higher resistance, you are going ot see the cable be warmer in that spot. But, odds are, the connectors were probably the source of the problem. But, you should see a connector that is having a resistance issue turn brown from the heat. Kinda like if you have a wire failing under the insulation, this will normally cause the insulation to discolor. It doesn't need to be much. You get a simply 0.1 ohm change and you run say 50 amps through that wire, that is a 5 Volt drop and a 250 watt heat source (think about how how a 60W incandescent bulb gets, now put 4 of them together). the voltage drop would definitely raise hell with the car.
@Thermo So, the old connectors are all connected to the new fuse box. I don’t see any discoloration of the pins where said connectors plugged into the old box either……BUT, I do see discoloration on the spot where the main power cable (the one that connects directly to the battery) connects to the box. Please see below: the red arrow point a to where the main power cord goes the bracket beneath seems all dark and purple
The images below are NOT from my NOS box , since it’s already installed…..it’s from eBay used boxes for sale , and that bracket , which is purple and discolored in MY old box is perfectly silver in the eBay used boxes….see below:
Spike, looking at that one metal bar that has rust on it, that could be your smoking gun. While it is not rusty everywhere, I liken it to a garden hose vs a fire hose. If you are filling a pool, do you want to use a fire hose or a garden hose? Most would say the firehose because it can flow more. This would be the battery cable. Bigger cable can handle more amps. Now, you could in theory raise the pressure to make the garden hose flow like a fire hose, but that is an extreme and in the case of your car, that would be raising the voltage way above what anything can handle.
I would say that you could take that rusty bar and between a wire brush and a little bit of sand paper, it could be returned to a silvery color. This would also apply to the terminals of the mega fuses and any lugs that attach to the fuse box. Like I had previously said, it doesn't take a lot to cause voltages to drop when dealing with high currents.
no rust at all. It’s just discoloration. The discoloration turns black towards the area where the main power cord goes, but not what I would call rust…..
this same bracket on used boxes, per what I am seeing on eBay, looks silver.
So are you leaning towards the problem being thr cord itself causing all the problems?
right now the car has a brand new fuse
box and a brand new power cord. So I am hoping I should be fine going forward, but it’s good to know for future reference
Aluminum does not discolor in that way and other metals are expensive, it must be some type of steel. It is possible the part is heated during manufacturing to get specific properties but it would be all one color. I think you had a very very hot connection there. Either a loose connection or the famous bad battery cables or both. If it was as hot as 500 F that is way over the temperature rating of those fuses it is bolted to so that could cause all sorts of electrical problems.
Interesting that the piece is clearly stamped with a 50 Amp rating but Jag uses it to connect power to a 60 amp and an 80 amp fuse. It could be carrying almost 3 times it's rated current.
Aluminum does not discolor in that way and other metals are expensive, it must be some type of steel. It is possible the part is heated during manufacturing to get specific properties but it would be all one color. I think you had a very very hot connection there. Either a loose connection or the famous bad battery cables or both. If it was as hot as 500 F that is way over the temperature rating of those fuses it is bolted to so that could cause all sorts of electrical problems.
Not loose- I am sure of that. It was on there tight on the old box ….So that leaves the cable itself . I guess I should just probably take that and move on, but I can’t help but wonder why so many used fuseboxes on EBay, from cars that probably never even had a single battery cable changed in their lives, don’t have this problem……... The only aftermarket thing I have in my car is my Alpine Apple CarPlay screen-so I hope it’s not that causing the problem.
Interesting that the piece is clearly stamped with a 50 Amp rating but Jag uses it to connect power to a 60 amp and an 80 amp fuse. It could be carrying almost 3 times it's rated current.
Good point about the colors. That does give a hint as to how hot it got at some point in its life. Also note how there is a very thin line that is colder/silvery. This is telling me that you had a very small contact area where the metals were pushed together, not simply very close. A piece of 22 gauge wire will attempt to flow 50+ amps. It may very well do it plus more. But, it comes at a cost. The cost is looking like a toaster heating element (ie, the current is so much, the wire gets hot). Same thing with a connection that has very little surface area making good contact. That fraction of an inch is like putting a piece of 22 gauge wire in a length battery cable. yeah, most of the wire is battery cable that can easily handle 100's of amps. But that small piece is working its butt off and as a result is getting very hot and causing a voltage drop.
As for the "50 A" stamp, sure, the metal is designed to only handle a max of 50 amps, but it will handle a lot more, but again, it comes at a cost (heat). Also of note, you don't want to put a 10 amp fuse on a load that runs at 9.9 amps. It may surge, or change slightly over time. You normally give it a margin to work in. The general rule is to put the fuse roughly 10% above its max. But, there are times where a higher rated fuse may be used. An example would be say HID head lights. They are 35 watts each (so, in a 12V system, they pull roughly 3 amps). So, you would think a 5 amp fuse would be more than enough to handle the bulb. NOPE. The starting surge (only lasts for a second or two) is up near 20 amps per bulb. IE, the starting of the HID pulls almost 250 watts (about 8 times the rated power). In a lot of cases, you will find each HID bulb with a 25 or 30 amp fuse. Now imagine your dash fan. It pulls roughly 25 amps when running on high speed. Now, imagine you are jumping in your car on a hot day and your A/C is immediately kicking into high gear. That fan is pulling a ton of power (in reality, it will be up over 100 amps, yet on a 40 amp fuse). This is where a fuse will take an over current for a finite amount of time. The higher above the fuse rating, the shorter the time period the fuse will take it. Now imagine the same situation where you are starting your car but now you have the dash fan, seat fan, engine coolant fans, etc all starting and trying to pull that initial surge. Yep, that bar is going to have to grunt and let that current pass and some engineer figured out that you have to have a mega fuse of 60 amps or 80 amps in various locations, even though under constant conditions, it is only going to a max of 50 amps. The newer XJ's have a 400 amp maxi fuse. My god, what pulls that much power? The car does when starting. It may be very short lived. Things may not get hot in that time. But the current happens. In your case, you had long term "near max" current pulls (you do live in Arizona, I am sure that dash fan gets a work out), now you introduce an area of less contact, the heat generated will now increase. You make some heat, now you start oxidizing the metal, that introduces more resistance, making even more heat.
Getting a little off topic here, but it will help explain my point, I work in the power production field. We routinely check how good electrical connections are using FLIR cameras. So, now imagine looking at a 500KV line and seeing the camera showing a hot spot. That is not something that you could measure really any other way. The voltage is just too high to do that. Or, we look at buss bars (metal bars 8 inches wide by an inch or so thick). What is the resistance of those? (hint, pretty much 0 ohms). BUt, you start passing 1,000's of amps through them, where they get bolted together will get warm. This is where you have to establish "what is warm but tolerable" and "what is too warm". This is your metal bar, but on a smaller scale. But ,the ability to measure a "high resistance connection" is just the same. You are talking on the scale of a tenth of an ohm if not hundredths of an ohm. Your back yard mechanics just don't have the tools to measure stuff like this. It would almost be interesting to have you get one of these FLIR cameras and take a picture of your 2 fuse boxes with the same load applied, just to see the heat difference. I know it would be a lot of work, but if you have the time.......... This is where I learn some of my things that I try and explain to others. Most can't imagine working around something pulling 1,000's of amps. Me, I touch pumps pulling 400 amps on a 4KV circuit every day of the year and don't give it a second thought. But, sometimes you have to think about how current can affect things and make them do very interesting things.
A few careers ago I was measuring automotive electric motor start-up current spikes. You aren't joking about 100 amps plus on a fan motor. For a few days we thought it wasn't much then realized our (substantial) bench power supply just couldn't dump current as fast as a battery. With one battery on a fan motor designed to pull about 20 amps in normal operation we could measure well over 100 amps at start-up. It was over 300 amps with multiple batteries, the 100+ amps seemed to be a limitation of the single lead-acid battery. Fraction of a second, but scary amount of current for ~14 gauge car wires.
dh53, the rule of thumb for most motors is a factor of 8. So, if you have a motor that runs at a continuous 20 amps, the starting current is normally around 160 amps (or 8 times the normal). Thank goodness copper is good and it can absorb some of these hits. Its when you make it work for a long time that things get "really interesting". LMAO. Fire, fire, fire!!!!!!!!!!!!!!
06-09-2024, 09:24 AM
