W203 Jump Start Wierdness

[Sonny Burnett]

hi everyone my wifes car went flat (the c240) as we went away and took the 210 and the battery died,
no problem i jump started it from the 202 all was fine she started right up without any issues, after i removed the cables i turned the 202 off and let the 203 run i herd a slight clicking coming from the battery/ABS area. it went for about 2 mins then stopped for about 5 mins then started clicking again, the car and engine revved freely and fine like new im just curious to what a little clicking can be??? anyone else had this?

 

[kwakdonut]

You jump started a 203 from another, running, vehicle?

Big no-no. Never jump start any new-ish Merc from another car with the engine running, can cause potential electrical problems! Jump pack is preferred or jump from another car but ensure the engine isn't running.....

 

[prprandall51]

You jump started a 203 from another, running, vehicle?

Big no-no. Never jump start any new-ish Merc from another car with the engine running, can cause potential electrical problems! Jump pack is preferred or jump from another car but ensure the engine isn't running.....

If you attach a non-running donor car to a car with a flat battery and then try to start the flat-battery car the end result is often just two cars with flat batteries. The donor car's battery charge will almost immediately drop to below the critical level for a successful start on its own.

If you follow jump starting procedures correctly I cannot see how electrical damage can occur to any car.

 

[dog68]

Could be a relay, that has been burned, so its sticking.

 

[SpikeUK]

When my battery went flat, the RAC needed to use a "Jump Pack" AND a running van together !!

 

[camerafodder]

Its OK to use a running vehicle. The battery will absorb any transients.

 

[markjay]

I believe that Black55 advised in previous posts against starting from another running vehicle.

Apparently the way to do this is either with a jump start pack, or from a standalone external battery (i.e. not connected to another vehicle).

I understand that this is an issue with CANBUS cars?

Having said that, are you sure the the 'clicking relay' noise is new? Perhaps it is unrelated, and it is just that you haven't been near that part of the engine recently, i.e. prior to the battery running flat?

 

[gunning]

its ok to jump older cars with the engine running but new cars is just abit of a no no really, there is a small risk of mucking up the eletrics but to be fair its minimal.

 

[gunning]

oh and the clicking noise might be the ecu shutting down

 

[renault12ts]

hi everyone my wifes car went flat (the c240) as we went away and took the 210 and the battery died,
no problem i jump started it from the 202 all was fine she started right up without any issues, after i removed the cables i turned the 202 off and let the 203 run i herd a slight clicking coming from the battery/ABS area. it went for about 2 mins then stopped for about 5 mins then started clicking again, the car and engine revved freely and fine like new im just curious to what a little clicking can be??? anyone else had this?

I always jump from a running vehivle.

But to answer your question, if nothing appears to be wrong...then there probably is nothing wrong. You are hearing sounds that you were just not aware of before.

Relax (unless all hell breaks loose ).

 

[prprandall51]

its ok to jump older cars with the engine running but new cars is just abit of a no no really, there is a small risk of mucking up the eletrics but to be fair its minimal.

We need more information - how, what, who...?

The electrical supply to a car can vary wildly from 14.2V down to 0V and the systems will not be damaged. So long as the jump starting is carried out correctly I still cannot see how either the donor car or the jumped car can be damaged since the voltage cannot fall outside of these parameters.

 

[BlackC55]

Its OK to use a running vehicle. The battery will absorb any transients.

Oh no it wont.

Time and time again I have seen 203's jump started and blown the SAM units. Frequent occurance i'm afraid.

 

[prprandall51]

Oh no it wont.

Time and time again I have seen 203's jump started and blown the SAM units. Frequent occurance i'm afraid.

Not doubting your experience, but how could that happen - unless the donor vehicle was detached prematurely and there was a system spike from the alternator reacting to the sudden change in battery voltage - but that would simply be poor jump-starting practice?

 

[camerafodder]

Oh no it wont.

Time and time again I have seen 203's jump started and blown the SAM units. Frequent occurance i'm afraid.

What causes the damage though? The quality of electrical supply is unlikely to be much different to that of the vehicle with the dead battery. Provided no-one makes a pig ear of connecting the jump leads it ought to be fine. I'm not disagreeing with what you've found, I'm just wondering what makes it happen. Batteries are very good at absorbing spikes and transients.

EDIT:
Snap!

 

[BlackC55]

It seems like voltage spikes are the cause. I have never measured voltage while jump starting a car as it is too risky. We always use a jump pack as the voltage is stable.

203's and 220's seem the most sensitive.

 

[stwat]

its ok to jump older cars with the engine running but new cars is just abit of a no no really, there is a small risk of mucking up the eletrics but to be fair its minimal.

It should't be done even on the older Mercs. It is known to damage the OVP relay and even at the very least, blow the fuse in it.

 

[prprandall51]

My understanding about jump starting is that - apart from the blindingly obvious problems of connecting the leads round the wrong way or shorting one by mistake - the two issues are:

1) People very rarely leave the two connected long enough (with the donor car at a high idle) to raise the flat battery's voltage prior to attempting a start (though there is no systems risk in this - just that the jumped car won't start) and
2) People often (very often) disconnect the two cars way too soon causing a system spike in both cars as the alternators react to the sudden, massive change in voltage.

I leave the two cars connected and running for about 10 minutes before disconnecting, I have never had any problems (though saying that is surely tempting fate...).

 

[camerafodder]

The only thing I can think of is that if connections are not made smartly and cleanly, the effects of high current arcing may cause problems with the sam's sensitive electronics via induced AC ripple or noise.

EDIT
Dammit prprandall51 you keep beating me to it!
I jump start using the same methods as you. Heck I've even successfully jumped the Unimog from my 211 on more than one occasion and that's a 24v circuit (bit of a trick) without any problems.

 

[Sonny Burnett]

ok people lets not argue if it is right or not. i have jumped loads and loads of mercs. i have 4 of them Never NEVER had problems

thats not what i started this thread for (its getting like the signature thread ffs)
so the car seems fine i cant hear it from in the cabin just outside the car if i listen closely. but the point is the clicking is there

i have a feeling it was there in the first place..

 

[BlackC55]

It is probably coming from the re-circulation valve. It has MOT written on top of it. It is normal for it to click too