Engine management and using jump leads question

mystic_trev

I know many of you Guys are well informed and I'm curious about the answer to this question! It used to be said that using jump leads can b*gger up the Engine management system. Is this fact or fiction?

Nodding_Donkey

It usually happens because people connect the jump leads with the ignition switched on AND the leads the wrong way round.

A very expensive mistake.

F1F93

I read in my vehicle handbook that jump leads are not recommended. Battery chargers are a safe way to start the vehicle.

Strider590

Fact is, with a car battery more than a few years old, if it's let to run flat, then it's probably damaged beyond all hope of repair anyway.

Jump leads and sticking it on a charger each night, do nothing but delay the inevitable and risk you getting stranded somewhere.

chrisw

It's electrical spikes which cause the problem, so as long as everything is turned off when the connections are made and the donor vehicle is idling away, the car with the flat battery just receives a steady voltage which is no different to its own battery (although around 14v rather than 12v).

TrickyWicky

Fiction IMO.

I've jump started tons of cars - from basics to those with very complex ECU systems and none have ever had a problem. I've used my own car as a donor plenty of times and it's always been ok. I've also jump started it many times and it's been ok - despite once shorting the battery while it was running - eek lol

forgotmyname

Trying to crank the engine over with a dead battery can do more harm.

Voltage goes down the amperage goes up.

Attach jump leads but triple check the cables are the correct way around + to + and - to -

Dont !!!!! foot around either otherwise you can get sparks. Just clamp them as quickly and firmly as you can.

Then let the running vehicle put some charge back into your battery. Dont attach the leads then instantly try starting it.

Also dont assume thicker leads are better. I had some leads that worked well. But tried somethicker ones and they were usless. Looking at the wires it was about 1/4 of the thickness as my thinner leads. Just had a ton more insulation.

My leads were just 8mm worth of copper strands. Little insulation.

[Deleted User]

forgotmyname wrote: »

Don't attach the leads then instantly try starting it.

I've always done that (jumping off a running car), and never had a problem.

EdGasket

Don't jump start modern cars. Remove the battery or disconnect one lead, then charge it. You can get away with jump starting some of the time but it can and does cause expensive damage to ecu's and other modules; sometimes the damage does not manifest itself straight away.

TrickyWicky

EdGasket wrote: »

Don't jump start modern cars. Remove the battery or disconnect one lead, then charge it. You can get away with jump starting some of the time but it can and does cause expensive damage to ecu's and other modules; sometimes the damage does not manifest itself straight away.

So how do you know that any damage was down to jump starting?

EdGasket

TrickyWicky wrote: »

So how do you know that any damage was down to jump starting?

Well for instance an ecu should generally last the life of the car but if say it went within two weeks of a jump start, I would conclude a high correlation between the jump start and ecu failure and this does happen.