jump started negative polarity car ideling funy and wont run

[Jordanjames]

My E30 316 touring has just come out of the body shop it was running Thursday fine.
It ran low on fuel and also the battery had gone flat. Upon starting earlier today the battery drained instantly.
(note I added 2 gallons of fuel just to make sure there was plenty in)
Stupidly I tried to jump start the car with cross polarity
It was sparking for a few seconds before I had chance to take it off.
The car now starts sounds terrible ticks over for a short while and then cuts out as soon as you apply revs it cuts out also.
The AA guy checked fuel pump and fuse for fuel pump, spark plugs, air mass meter and all was okay


Is it possible that positively charging the negative on the battery has caused me to fry the ECU or something electrical?

Many thanks Jordan

[Brianmoooore]

I think it's unlikely that you have damaged anything important by reverse connecting an external battery, although it's possible that the ECU will have lost its idle speed settings, and need to relearn them. This will have the effect of making the engine likely to stall when pressing the clutch or moving the gear lever to neutral when driving.
The alternator is probably the most vulnerable component, and this, combined with the still connected flat battery, will have dealt with most of the reverse current.
Has the car run properly since returning from the body shop? What sort of work has the shop been doing?

[Jordanjames]

No the car hasn't left as I was due to pick it up this morning. We knew the battery was flat and I made the mistake of thinking brown was positive (I am an electrician) when we tried to jump it.

. The car had been driven in and out of the garage most days and my friend had given it a decent run in the middle of the two week period it was there.

They have had the bonnet off for a respray but the rest of the work was all lower will and arch touch ups.

Thanks for the good reply, what do you suggest I do? If it's not something simple I can get it to quarry motors Monday morning.

Thanks again

Jordan

[Jordanjames]

Every time we put the throttle on it cuts out as well. When it is ideling the car sounds terrible like its missing.

[Slow]

Sounds like a ecu problem?

Are you still using the current battery? Maybe its fucked and wont give a proper spark?

[Brianmoooore]

Cutting out when applying throttle, after work has been done, often turns out t be that the AFM plug hasn't been refitted.
Poor idle in similar circumstances often turns out to be a split in the large AFM to throttle body hose.
Any chance that they've had the air filter assembly out to gain access to that area?
Have you checked the battery voltage when the car is running and/or charged the battery?

[Jordanjames]

All the plugs where checked. Also when I asked them they hadn't dosconected anything either.
The car had started that morning but the fuel was low and the battery went flat.
The battery voltage wasn't checked but the aa guy had his battery pack connected for an hour and we tried running with that but still
No joy.

Thanks

Jordan

[Jordanjames]

is there a possibility that it ran so low on fuel that there is some shit stuck in the system? i tested the amps across the fuse connections for the fuel pump and it was drawing 5amp which i understand to be correct?

could there be some dirt potentially hampering it.

thanks

Jordan

[pianist]

I would go with Brian on this one, the alternator may be burned and causing it to misbehave

[pianist]

Also check all your earth connections like body to engine etc.

[Jordanjames]

Thanks for all the replies guys!

Got it into quarry. Turns out it wasn't anything to do with my cross polarity jump start.

The cam shaft sensor had been shorted out due to the cable coming loose and the cam belt
Had burnt through the insulation and was causing miss reading and shorting it out.

It had obviously been happening for some time and it was just unlucky that it happened to break at
The same time as I was playing with the battery.

Anyway it was an easy fix for the quarry lads and the car is now back on the road for Christmas!

Jordan

[Brianmoooore]

Two problems with this. Your car doesn't have a cam shaft sensor, and there is no wiring that could possibly be rubbed through by the cam belt!
A more likely, and a very common fault, is that your crankshaft sensor wiring has been damaged by the fan belt (or more likely the water pump pulley, driven by the fan belt), as a result of the fixing clips being broken.

[pianist]

I think this is what he meant lol

[Jordanjames]

Two problems with this. Your car doesn't have a cam shaft sensor, and there is no wiring that could possibly be rubbed through by the cam belt!
A more likely, and a very common fault, is that your crankshaft sensor wiring has been damaged by the fan belt (or more likely the water pump pulley, driven by the fan belt), as a result of the fixing clips being broken.

Yes sorry, this is right, I was tired and had a third hand message when I wrote this.

Thanks again