I would like to get a conversation going about jumpstarting your car. It has been identified several times that jumpstarting a Jag is not a good thing to do. Now I know that we have a right and wrong way to do it and maybe that needs to be discussed. The reason I ask is that I was in Lowes and saw this unit “Pilot InstaBoost 400-amp” car battery jump starter and I want to see what input I get on this. I like the idea but do not know the possible effects.

Link http://www.lowes.com/pd_573361-74342...Buy_Now_Search

 

Gus,

Good idea.

I and others have previously posted the Jaguar recommended procedure for jumpstarting in reply to a number of posts - usually when someone has got it wrong and done some damage to their vehicle electronics!

I've taken a screenshot from the Lowes link you posted to make sure the 'InstaBoost' info is available if the link disappears:



We have similar devices available in the UK. Be interested to hear if anyone has used them.

For the benefit of anyone not sure of the Jaguar recommended method, here is the procedure:





This is taken from the 2005 XK8/XKR Driver's Handbook but is typical for all models.

Graham

 

I will get this going with an electricians point of view of the whole battery jumping bit. Lets first start off with what a battery is capable of doing when in a discharged state. When it comes to loads, not worth much. But, the problem comes in when you have a source that can supply a large current and you connect it to the dead battery. The dead battery is going to attempt to pull as much current as it can to bring its voltage up to whatever the sources voltage is. This is part of the reason why you will hear people say that it is good to have both vehicles off when trying to jump start a car with a dead battery. In theory, the battery could pull hundreds of amps. As you can imagine, the supplying car would not like this. In reality, you are probably limited to around 100 amps as you have the resistance of the jumper cables providing a big limiter. This would be about the only condition where I would recommend having a set of say 10 gauge jumper cables. Granted, be ready for those cables to get hot as they will be passing lots of current and they are going to be dropping some voltage. Even if you assume a 100 amp pull and the cables are dropping 1 volt, the cables are putting out the heat of a 100W light bulb. This is not good.

If you run a heavier duty set of cables, the heating issue is not quite as much of a concern due to the cables having less resistance (therefore a smaller voltage drop) and they will absorb the heat a little better as they have more mass. But, the problem now becomes the limiting component is now either the supplying car's electrical system (could easily overload the alternator and damage that) and/or you can spike the dead car's electrical system and take out any computer and/or damage the battery. Atleast if the working vehicle has its engine off, you are going to get a smaller current and therefore less risk of damaging something on both vehicles.

A general rule of thumb I use when working around automobile batteries is a 100:1 rule, more easily thought of is the 10:0.1 rule. For every 10 amps going into/out of a battery, it will change its voltage by 0.1 volts. This is fairly true when looking at batteries at 12.6 VDC or below. When you start getting above 12.6 VDC, the battery starts exhibiting different characteristics due to the chemical reaction that is going on. That is what allows the battery to go up to 13.7 VDC (normal alternator output voltage) when the engine is running without the battery sucking up 110 amps from the alternator.

So, putting this to theory, if your battery is down around say 9.0 VDC, if you have a running car, the alternator is going to be hit with about a 360 amp load (12.6 VDC to 9.0 VDC, remember the characteristics of the battery and then using the 100:1 rule). As you can imagine, this will not only create a nice spark when you go to connect, but the electronics are not going to like the fluctuating voltages.

From personal experience, I went to jump a friends Honda Civic with my Ford Expedition. I had a good set of cables (some 4 gauge cables) and I connected my truck to his car. Needless to say, his car came right to life and he damn near sh!$ himself when he went to start the engine because it saw the 13.7VDC of my truck on the starter. The starter got a little warm (could smell it) and his instrument cluster ended up doing some funny things because of the voltage my truck was putting out. But, that is the only time that I have ever seen a car behave erratically.

 

I'd like to know the theory of why Jags are more sensitive to jump starting than other comparable cars. Never heard this idea till I joined the forum.

 

To be honest I think it is the way they go about doing it that is a problem.

 

Now, we can talk about the problems of not jumping a car correctly. The most common thing is connecting the negatives and positives the wrong way on 1 car. If you make an assumption that the jumper cables have a resistance of 0.1 ohm (which is actually pretty high for jumper cables). If you have one battery at 12.6 VDC and the other drained to 9 VDC, you have a difference in potential of 21.6 VDC. With the jumper cables, you are going to pull 216 amps (a nice spark will be present), not to mention you are going to take both car voltages and effectively drop them to zero. Cars do not like having their voltages drop to zero under heavy current conditions. it isn't quite so bad with the power turned off and you disconnect the battery (hence why you are seeing a lot of shops when they go to replace your battery that they will put a second battery on the terminals or in the cigarette lighter so the computers all see a constant voltage even when you disconnect the normal car battery).

As for attaching to the ground of the car or to the negative battery terminal, there is some logic to this. The ground of the car (specifically the ground on the engine) is the better point to connect to as you won't have any losses from going through the ground wire of the car back to the battery. The engine block provides an extremely low resistance due to the amount of metal that it contains. The big thing you have to watch out for is connecting the jumper cables to a rusty post. Rust has a fairly significant resistance (relatively speaking here) compared to even the ground cable going to the battery. So, the rusty bolt will create a hot spot and can lead to welding of the jumper cable to the post because of the heat created. it also makes it very difficult to jump start the car since your voltage drop will be at that rusty bolt, not across the starter/battery.

If you have other questions, shoot them my way. I will try and answer them without getting too technical.

 

MIkey, when it comes to Jags being more sensitive to jump starting than other cars I think comes down to how much the car designer is trying to push the envelope of technology in the vehicles. Modern day electronics are very shock sensitive. So, rapid voltage changes and whatnot are enough to damage them. Now, you start trying to squeeze a little more out of the car by using a faster computer, you are going to need the later and greater technology. So, it is going to fail more often than say a car made back in 1970 with no computers in it on the same jump start. The more consumer based cars (Ford, Chevy, Dodge in relation to Jaguar) are using older technology (hence why they are cheaper to a degree). So, the electronics are a little bit more robust.

Please keep in mind in that I am comparing older electronics and newer electronics that were made in the same year. You take a computer from a 1989 Ford T-Bird and compare it to that of a 2015 Jaguar XJ, you will find that both computers are going to suffer about the same rate of failure on jump starts because both were using "cutting edge" electronics for that time. So, they both suffer from weaker electronic parts. You get a remanufactured computer that has been upgraded to have modern day components, the 1989 T-Bird computer is going to handle jump starts way, way better than the new Jag will.

 

Betcha you're right.

 

So what is the right way and can a unit like the InstaBoost work? I need to reread Thermos post.

 

To be honest I think it is the way they do it that is a problem. At the moment I am unable to put my finger on the recommended procedure.

 

Don't hook it up backwards is the message.

 

It occurred to me after reading further posts from Gus, Chris and Mike that we all know how to do it but many may come to this thread to find out the correct Emergency Starting procedure.

I've therefore revised my post #2 to add the Emergency Starting procedure from the 2005 XK8/XKR Driver's Handbook. My only reason for selecting this model and year was the PDF is the best quality from the handbooks I have.

Graham

 

Thanks for that Graham. That procedure is virtually identical to just about every other OEM's.

 

Thanks Graham, all that info is good a good read and good to have.

I think sequence is important when installing the cables but knowing what you are doing and how to go about it is equally important. If I recall we had two people that connected the positive the negative (reverse polarity) and that was not a good outcome.

When I read the procedure I begin to think about the connection of the jumper cables, how many place the cables on the terminal without sparking and or re-striking. I often thought it would be a good idea to have a switch in the jumper cable that enables you to attach the cables and then flip the switch to get the power then turn it off.

This leads me to the portable booster you can install the cables correctly (it has a reverse polarity indicator) and press the button to provide power when you are ready (no power connection when installing the cables) when it is in place you push the button and you start the car. I think it is a clean and accurate way to go. However I am not totally convinced and that is why I want an open discussion.

Another thing to think about is when we do a hard reset. We remove the cable on a good battery and short it to the other cable then reinstall it back on the good battery. Why is that not a problem?

 

The hazards of hooking up a battery with reverse polarity are mostly obvious and again are not unique to Jag. The damage is not restricted to modern or fancy cars either- my other hobby is old Corvettes (pre EFI and HEI) and at least 2-3 times per year we hear of someone who connected their battery backwards. Usually lots of smoke ensues and maybe $1K in parts is the result.

Jag goes to great effort to encourage owners not to use the negative terminal on the battery. I can only think that they worry about the presence of hydrogen vapours and sparks. Trunks/boots are better sealed than engine compartments so there is the possibility I suppose.

I ventilate the area as best as I can beforehand.

 

Not an expert by any means, but I have used a portable jump starter on a 2007 X-type, 2008 PT Cruiser, and a 2000 Saab 9-3 with no adverse reactions.

 

Does it have an option to connect to the battery prior to starting after the cables are installed?

 

My experience in modern cars is jumpstarting will not help a dead battery and usually they go all at once. I just had this happen to me. Admittedly, the battery was 7-years old, and even though I mentioned it to my service advisor during the last main dealer inspection, he said everything check out fine so there was no need to replace the battery. Lesson learned. Anyway, the car sat in sub-freezing temperatures for 4-days outside at the airport and when I tried to start the car it just ticked-ticked-ticked, even though all the lights, bells and whistles came on. An attempted jump start from one of the aforementioned boosters did no good, so I left the car for another (cold) night and called the tow truck in the morning. The tow-truck driver, of course, attempted the same and also from his truck mounted jumping station (BIG alternator) and the result was same again; lights, bells and whistles, but no start. In the end, the car was hauled to the dealer and the battery replaced. Bob's yer uncle.
However, comma, the dealer failed to reset the windows, the clock and did not mention the garage door opener would have to be reprogrammed, so last night when I came home from yet another trip at 12:30 aye-em, I could not open the garage door, thus precipitating me waking my wife by banging on the front door so she could open the garage door to let me in.
Now, the point I'm trying to get to, is I recently read a tech submission in the JDC mag, which led me to believe there is a whole procedure required to "retrain" the ECM when a battery is replaced. I guessing since my dealer's service department did not reset anything else on the car they did not "retrain" the ECM either. What would be the long-term consequences of not doing so? Should the car go back to "zero" and be retrained? Thoughts?

 

Disconnecting the battery loses the learned fuel trim adaptations which default to standard on reconnection. These will reset within a short period of driving.

Many of us with earlier models have long been used to the reset requirements after a battery disconnect/reconnect:

1. reset window limit switches
2. reset audio presets
3. reset clock
4. reset idle speed

All of these can be carried out by the owner but your XF adds a further complication - the battery monitoring system. According to the Workshop Manual, the vehicle has to go on the dealer (or equivalent) diagnostics to reset this.

Graham

 

Well, opinions are like you-know-what, everybody's got one. Here's mine.

While those little batteries, like the one Gus linked to, are a wonder of battery technology, their usefulness as advertised is questionable. Even the tool guys that come around to the dealership hawk these 'boosters'. Think about it, even the documentation that comes with them states they will recharge a smartphone 4 times, and the current iPads just once. I hardly think four smartphones will jump start a car. :-) On the other hand, as a test, we did jump start a few cars with this thing. But the only car that SUCCESSFULLY jumped, was at an ambient temp of 70 deg. F., and the battery was GOOD, just discharge to the point it couldn't start the car. Any car that actually had a failed battery, or was at low temps, was a lost cause.

So, in my mind, I'll spend a couple hundred bucks and get a booster like a Jump-N-Carry JNC-660 that will truely do the job. I think it's rated at 1700 peak amps. Works great.

As far as connection for jump starting, following the rule that the positive is connected to the battery terminal and the negative is connected AWAY from the battery, preferably at a solid point on the body or engine, you should be in good shape. Connection at the "T" bolt for the spare tire might work, but I still prefer a more solid piece of metal. I wish they did not advocate that in the owners manual.

Connecting to the negative terminal is not a good idea for two reasons. One, that makes for a spark adjacent to the battery. Due to the gases that are produced by battery action, you don't want a spark there. I've had batteries blowup on me over the years, ain't pretty. And two, newer cars do have a Battery Monitor Module, usually on the Negative cable terminal, that can be damaged by sparks or static electricity. Not worth the risk to make the final connection there.

Others will chime in.........