steaditim

Greetings all

The owners manual for the 928 describes using battery jumper cables, but I've heard stories of control modules getting fried.

Any thoughts on this?


Tim

Shane

Yes it is doable but not really recommended. If you have no other way then hook up to another car but with out it running, this will help protect your electronics as well as those of the host car.

JohanvdWalt

Yes you can use it on any car BUT do it right

1) Connect the negative to a good earth on the car with the dead battery, NOT to the dead battery itself (it will suck up to much power), then connect it to the live battery.
2) Now connect the positive leads to both batteries.
3) Start the car with the fresh battery and keep it to 2500 - 3000rpm.
4) Now start the car with the dead battery, do not turn it over for longer than a couple off seconds at a time - the cables will over heat and not carry enough current.
5) VERY IMPORTANT turn on as much electrical equipment as possible on the car with the fresh battery before removing the cables. This is where most people go wrong and blow the electronics.

Why? well the easy way to explain is compare it to a tap in your house. The fresh battery is pushing out full capacity to the dead car now you instantly close the tap by removing the cable, just as you would create pressure in your water pipes at home you create a overflow off currant to all the electrical systems in your car and something will blow unless you give that current some work to do.

Hope its understandable

Johan

Lizard928

ok here is the truth, turning on elect componants does that is righ JACK SQUAT,
you should attach the jumper cable (dead car) ground wire first, it doesnt matter if it is the battery or a ground point, it is all the same, then attach the positive (dead car) then attach the gound to the good car either battery or ground again it is all the same, then the positive to the good car, hold the vehicle at 1100rpm anything else (unless modified from factory is a waste gas) and sit like this for about 5 min, then TURN OFF THE GOOD CAR, and fire up the dead car, now disconnect the cables as you put them on

now to clear up some things if you put the battery cable on a ground point instead of the battery this will do nothing UNLESS you have bad grounding in the vehicle and then it isnt going to be charging properly.

do not try to start the dead vehicle though with the good one running it will draw too many amps for the alt, and could cause a problem

Red UFO

I've had to jump my shark quite a few times and treat it as I do any car. I doubt it will do any damage unless your doing something wrong. If you use common sense I don't see a problem with blowing out your electrical. I'm sure it could happen but I'll bet this is more urban legend than fact.

Anyone here have 1st hand experience with something blowing out? Or is this just paranoia?

hacker-pschorr

I have two charged jumper packs, one in each car. If you don't have one, you should. My mom's caddy had a dead battery few months ago. My bro-in-law insisted on using his new H2 to jump it. The H2 didn't give off enough to turn the caddy engine over fast enough. The jumper pack fired it right up. I think his jumper cables were quite old, might have had something to do with it. Either way, jumper packs are some of the best items to have lying around.

Cameron

Red UFO,

I had a '90 S4. Stereo shop ran the battery down and jump started the car at the battery terminals while the battery was still connected (instead of using the jump start terminal under the hood or charging the battery while disconnected from the car). They fried the fuel injection brain - $1500.

I was able to get them to pay for it, but it took me 6 months of 'negotiating'.

Your car is an '83 so you do not have an LH Jetronic Computer in your car. Perhaps someone on the board knows if an '83 has a similar risk re jump starting.

.....Cameron
'91 Euro GT

Red UFO

Cameron,

Thanks for the story. Did you have to wait 6 months with no shark?

There are right and wrong ways to jump a car. As soon as it fires up I disconnect as fast as I can. But if they were a stupid idiot then they can blow up just about anything.

SteveG

http://uuhome.de/william.darden/carfaq6.htm

Everything you could ever want to know about all kinds of batteries there. They say connect the neg of good battery 3rd, and the fee end of the neg cable to GROUND of weak batt car, not the neg pole of the weak battery.

NOTE: there are some discrepancies with advice posted here.

Gretch

I have jumper my GT with an other car perhaps a half a dozen times, the other engine usually has been at idle speed, and I have always used the under-hood terminal and the cross member bolt as attach points. I have never had any problems. I have, on many occasions, charged the battery in the GT using the same attach points. The Porsche battery charger (trickle charger) is designed for this set up, since unlike the 911, the 928 cig lighter is wired through the ignition switch.

I have experienced the situation where it takes a few minutes of connection via jumper cables, for the car with the dead battery to turn over. Question for the wire scientists here, why does the delay occur?

Cameron

Red UFO,

Since my 928 is my daily driver, no I didn't wait 6 months to use the car. That is how long it took me to get the $$$ from the shop.

I agree with your comment about how easy it is for some people to blow things up unintentially - literally or figuratively. Truth is stranger than fiction sometimes.

.....Cameron
'91 Euro GT

Tahoe Shark

So, have we come to any conclusions about the real proper way to jump start the Shark?

dr bob

The reason for using a chassis ground point instead of the battery terminals is to avoid having a spark right over a battery that may be generating a lot of hydrogen as it is charged. Following that thought line, the grounds should be connected to the chassis. Continuing that thought line, the ground connection at the chassis, away from the battery, on the car that is supplying the jump-start current, is the first connection to be lifted.

Lead-acid batteries generate saturated vapors that include a very small amount of acid carryover from the water heating, plus hydrogen and oxygen vapors. In a modern battery, the satutrated vapors are condensed and the water is returned to the cells, usually carrying most of the acid back with it. But the hydrogen and oxygen components sit in the space above the plates, and when a battrey is charged rapidly they may sneak out and sit on top of the battery. Add a spark from a jumper cable, and the flame path moves toward the batetry case and those vapors. The rapid expansion in the closed space will try to expand the battery case, and the fun starts. If the case holds the expansion, it might just get 'bigger'. If not, you get a pretty good amount of acid spraying around in a hurry. Kind of like a small grenade, with acid as the shrapnel.

My Explorer charging system runs at about 15 volts. Ford says this is within the normal range. But it's right on the edge of what the Porsche electronics will tolerate.


So, the best way to recover from a dead battery is to disconnect it from the car and charge it. Outside the car is best, especially if the vapor vent tube has been removed from your car at some point. The Group 48 batteries have a vapor vent port that should be tubed out of the battery compartment so that those explosive vapors don't accumulate.

If you must jump-start the car, try it with the cables first, from a car with the engine not running. This takes healthy jumper cables, not those wimpy 10-gauge bargains you found at K-Mart for a few dollars.

If the jump-start doesn't work, let the donor car's alternator charge your battery for you for a bit, with battery ground strap disconnected. This requires that you connect the jumper cables directly to the battery ground terminal and the battery positive onyour 928, but still lets you follow the rule in the first paragraphs about lifting the donor car's ground cable from the chassis first. When you think that you have sufficicnt charge, shut off the donor car's engine, reconnect your ground strap at the frame, and start the car. Once the car is started, disconnect the donor car ground jumper cable, the victim car positive jumper cable, then the other two connections in no specific order. This way your expensive EFI brains won't be exposed to the donor car's high-voltage issues.

------

A few months ago, the SoCal 928 Owners Clug had a fun run drive the day after the Sharktoberfest. I was sweeping the rear, since I was not in any competitive mood with the rev limiter in the right seat set pretty low. As we almost all pulled away at the start, one of the cars in the group was stranded by a dead battery. Parking lights left on for 20 minutes killed it. In spite of being a good Eagle Scout and all, I was not prepared for this simple problem with a set of cables. Victim agreed that the Auto Club was a valid option, so Karen and I motored off sedately to meet with the group at the first waypoint. The car was eventually started and they met us for lunch, but they missed the drive.

Lesson Learned: Don't rely on that old battery to keep you going dependably. Batteries are not reliable after four or five years, especially if the car is not driven regularly. My S4 told me a few times that the battery was weak, but I ignored the warning signs (reset codes in the digital dash display) a few times until I was stranded in my own garage once. Easy cure, jump in the other car and get a new battery. But many are not so lucky. It would be much better to replace the thing before it strands you.

Other Lesson Learned: Add a set of jumper cables to the collection of stuff that rides in the spare wheel. Doesn't take a lot. I grabbed some 6ga cable from a jobsite, added some clamps and some shrink tubing insulation, and made a compact set that fits nicely. I also found some quick-disconnect things at a supply store, kinda like big polarized molex connectors. I use them for maintainer/charging cables for the boats, and they will adapt nicely for the 928 I suspect, should I get a burst of extra energy someday. Until then the mini jumper cables will do the trick.


Do your electrical system service annually, per the Wally recommendation. Mine is overdue since it hasn't been driven in a couple months, but as soon as I have the space it will get the treatment. Maybe the camera will be on this time and we'll get a few pictures for an OC Forum write-up.


HTH!

Red UFO

Cameron thanks for the horror story.

For me I don't have patience for 6 months. I tend to lose it on the shop less than 48 hours. If you don't take care of business right away usually you never get things done right. 6 months later I'm ready to lob ****** at the repair at 2 AM if not burn it down.

SharkSkin

Well, I'm not a wire scientist, but that's OK since what you describe is not necessarily an issue with the wires.

What can happen is that with a really dead battery, the dead battery is more of a load than the starter, and it draws so much of the power from the other car that there is not enough left to turn it over. Once the dead battery fills up a bit, the balance shifts and you are able to turn it over.

S