Giving my car a boost...

I was stranded the other day ( and no not at the Drive-In (que the Grease music)) nad I aske about 6 people if they could give me a boost…you know the standart hook up the Jumper cables battery to battery and supply me some juice. Every single person refused saying that it would dammage their car computer. Is there any truth to this? Is this a consipracy by the auto makers and the towing companies to line their pocket with my hard earned cash?? Some help please!

There are only two things that are infinite…the Universe and Man’s stupidity…I’m not sure about the Universe though.

It can damage a car’s computer if done improperly. Improperly would include simply hooking up the two batteries negative to negative, positive to positive. This can be made even worse if that is done in the incorrect order.

The proper way to hook up a jump-start on modern fuel-injected cars is to first hook up the + on to the dead battery, then hook up the + on the good battery. Next hook up the - on the good battery, then hook up the - wire to a ground on the car with the bad battery. Do NOT hook up the - wire to the - terminal on the battery that needs the jump. You should be able to clamp the - wire on any bare metal surface, but its best if you can hook it up to the wire that grounds the engine block to the chassis. After you have made all the connections, start the car with the good battery, then start the car needing the jump. Lastly, remove all the connections in REVERSE order.

Anybody who wouldn’t give you a jump either doesn’t know how to give a proper jump, or they were just inconsiderate SOB’s.

aint modern technology grand? How hard would it be for the manufactorers to add a switch “jumpstart” that would put a diode in the circuit to protect the lil black box? Speakin o which even in the old days, well not the OLD old days of generators, just back to alternators with built in voltage regulators it was possible to hook up wrong and blow a diode. since that was all part of the alternator it usually meant a new alternator for the jumper.People who know how to repair stuff instead of replace parts have themselves been replaced by
MR Goodlookitupinthepartsbookandboltiton.
“sumpthin wrong wiff yore car? Let’s replace this part and see if it fixes it.”
PS Buy a GOOD set of heaviest gauge cables you can afford. Those thin cheap ones get HOT! insulation melts sticks to the paint job. Maybe even catches on fire, man, that was an adventure.

“Pardon me while I have a strange interlude.”-Marx

Anybody who wouldn’t give you a jump either doesn’t know how to give a proper jump, or they were just inconsiderate SOB’s.

I know the proper procedure, just as you describe.
Last time I gave a jump, about ten years ago, the guy grabbed the cables at his end and re-connected them. Backwards. Cost me 140 bucks for a new alternator. He got his car started and drove away.
No more Mr. Nice Guy. Call AAA.

Work like you don’t need the money…
Love like you’ve never been hurt…
Dance like nobody’s watching! …(Paraphrased)

That sucks. I definitely would have told the guy to pay up for getting the wires wrong and frying your alternator. That’s why if I’m giving the jump, I call the shots. I’ve given lots of people jumps, and have never had a problem.

Why is it necessary to hook up the last connection to a metal part of the car and NOT the (-) terminal on the battery ? Electrically speaking, they’re the same. Ground is Ground ! The reason they tell you to do that is because of the chance of a hydrogen explosion instead of damaging the car’s electronics. But with modern batteries being pretty well sealed, I think the “hydrogen explosion” idea is an old mechanic’s tale left over from the thirties.
I don’t seem to hear about a lot of people being maimed or killed jumpstarting cars.

You can’t push a rope

Docdec, You are correct that it is pretty hard to cause a H2 explosion w/ modern batteries. But, 1/10000 is not 0. It does happen. I’ve seen it twice, and it can really cause some damage. Why take chances?

Doctordec brings up a good point why do you have to ground the cable instead of hooking it up to the “-” pole. as he puts it a ground is a ground is it not?

There are only two things that are infinite…the Universe and Man’s stupidity…I’m not sure about the Universe though.

Well, having only an '83 Nissan Stanza (a nearly extinct animal (carburetor & older alternator)) I’m not up on new cars, but voltaire seems not to be referring merely to a rare problem with H2, but to the interposition of some electrical component/module between the negative terminal of the battery and the engine block. If there be such a component, I wouldn’t know which side of it the negative side of the alternator output would be connected to. mr. john refers a “lil black box” but doesn’t specify where it exists in the circuit. He then implies that new-car alternators have external regulators, so I would assume the box he refers to to be a regulator. Then again, not knowing mr john, maybe the box he’s referring to is some kind of fuel-injection control circuit which has nothing to do with the jump-start task. In any case, before getting involved with jump-starts to or from new cars, with or without fuel injection, I’d want to know the possible battery-supply and charging circuits that are around these days.

Of course, there’s no way electrons (or ions in the battery) can ever know whether you clamp any given cable first to the dead battery and then to the good one, or vice versa, so that’s of no consideration at all. And if nothing other than the cables completes any circuit between the two cars, it also certainly doesn’t matter whether you hook up the plus cable first or the minus one. Mention of these concerns does make me wonder about the legitimacy of the concern shown here as to where the negative cable is clamped on the car with the bad battery. This practice is probably good in general, though, in case the “bad”-battery ground cable has high resistance and the starter on that car is also returned directly to the block, as it should be. Starting the car with the good battery first, of course, always has been the proper thing to do, and it’s usually best to rev that car up somewhat about normal idle.

Ray (EE but no expert on cars)

Patricinus, lead-acid batteries produce charge by chemical reaction. A byproduct of that reaction is hydrogen gas. If there is going to be a spark (that might ignite the hydrogen), it will be at the point of the final connection (or first disconnection). Therefore, the connection should be as far from the battery as possible.

Ah, I used to just give it a push, when you get a roll going, you can get it started easily with a shift. Automatics have to go a bit faster [20mph] but I haven’t tried that.

If you think about it, just putting those two wires battery to battery is quite safe if done right.

I haven’t given it much thought but if you connect two batteries like that doesn’t that give 24 volts to the original car?

      • I am informed that you cannot start an automatic by pushing it at all. I have heard the same story about pushing it “20 or 30 miles an hour” but I have never seen it done, or heard of anyone trustworthy I personally know claiming to have done it.
  • The reason is that the hydraulic pump that supplies the pressure to switch the gears runs off the engine shaft, and pushing the car only spins the output shaft. Hence, you can push the car as fast as you like, but the engine isn’t gong to spin, and the shift pump isn’t going to spin, and the transmission will never shift out of neutral (which it is designed to “fall” into in case of pressure loss). - Now, there might be some really old, or maybe some foreign car that it would work on (I dunno for certain that no car can do it), but with typical Detoit iron, forget it. - I read this somewhere (Cecil?), and then asked a real, professional mechanic. He agreed.
      • I don’t know that jumping would do anything to a car’s computer.
      • Jumping another car is definitely bad for your car’s alternator [assuming yours is the car that is running], and unless lives are at stake, you shouldn’t do it. The reason is that the alternator in your car is designed for a particular amount of current flow, say, 60 amps. The problem is that when you hook it up to a dead battery/car, there is no load on your car’s alternator (because the other battery has no charge) and for a few seconds it will delver far more current than it was intended for, say 300+ amps. Probably won’t do anything the first time, but the damage of doing it again and again accumulates; your alternator don’t “heal”. - That’s why when you buy a new alternator or battery at the auto parts store, they offer to charge your battery for free - they want to keep you from burning out your (or anyone else’s) alternator by starting from a dead battery. - MC

MC, I don’t agree with that alternator idea.

That is how you get a car going, it works just fine.

But then the original poster did NOT say what type of car they have. tsk. What are we, mind readers?

The car is a 93 Intrepid ES. So more mind probes it’s starting to give me a headache.

Back to the Hydrogen explosion with lead acid batteries thing again… I thought, and I know you will correct me if I am wrong, thay they didn’t make “lead-acid” batteries anymore…have we not advanced beyond that in 100 years of motoring?? ( What I wouldn’t give for a sit down chat with Tesla right now)

There are only two things that are infinite…the Universe and Man’s stupidity…I’m not sure about the Universe though.

Back to the computer. . .

Is that a valid concern that it might “blow it out” someway?

nope, 12 volts, they’re in parallel.

MC, While jump-starting isn’t neccesarily good for your alternator/regulator, I would never turn someone down on the basis that their life was not in danger. Helping another human being is (to me anyway) worth far more than the cost of a possibly burnt-out regulator or a $13 diode assy. Besides, I’ve jump-started over 50 cars w/ my current setup, and no problems.
Push starting an automatic is possible But the trans has to be modified to do it (circle track cars are often push-started automatics). W/ production models, you’re likely to damage the trans severely just trying. So don’t do it.

Patricinus, Nope, still lead-acid. Materials have advanced significantly in the last 20-30 years, but the chemical reaction is the same.

As to the original question. As long as you do it correctly, the computer and sensors should not be adversely affected by jump-starting. There will be a voltage/current spike when connecting, but the battery itself is a pretty good filter, and the components are designed to handle it. When in doubt, check out the owner’s manual.

Repeated again for those with hard heads:

  • Go to any auto parts store and ask. Alternators have a little sheet of instructions included telling you not to jump start your car from a dead battery for this very reason (presumably if your alternator failed, your battery will have no charge).
      • I do not believe that you can charge 50 dead batteries with one unprotected alternator, which, if you jump-started “over 50 cars”, is basically what you would have done. - MC

In response to MC…

I had an old International Scout with automatic that I had to push start about 50 percent of the time due to broken flywheel teeth. I used to only park on a hill since it never started on the flat even if King Kong pushed it. Get it up to 15 or 20 and drop it in drive. I’ve never tried it with a newer car because I’ve also heard it’s a waste of time to try.

“What Ho ! Bring on the dancin’ girls !” Chubby


I’m not sure what you’re talking about…why would I try and jump my car from a dead battery? I think you’re a little mixed up on the whole jumping process.

When I hook up the cables, and start my car, all I’m doing is providing enough juice for the other car’s starter to spin and get the engine going…at that point, the other car’s alternator will provide the current to keep their car running. And their alternator will re-charge their battery…that’s why if you’ve got a dead battery, and get jumped, you should wait about 20 min. before shutting your car off. So your battery has time to charge.

“Love thine enemies…it really pisses them off.”

Someone mentioned earlier that…hmmm how do I put this…size doesn’t matter but thickness does? (making reference of course to the jumper cables) The thicker the wire the better off you are? I am not trying to be stupid here just curious but could you jump a car with just about anything as as it conductc electricity?

There are only two things that are infinite…the Universe and Man’s stupidity…I’m not sure about the Universe though.