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MG MGF Technical - Bump Starting (NFC)

Having a debate with someone.

I've always been told not to bump start a modern car as it will allow unburnt fuel into the exhaust system which would damage the CAT etc.

Friend says this is rubbish as when you turn the engine over with the starter it will pass unburnt fuel into the exhaust anyway!

Who's right and why?
Bob Millar

He's right, Soon there will be soneone along to say 'but if there isn't enough power to ignite a spark, to which I'd say 'or a fual pump or injectors'. Yes there might be more fuel that ends up in the cat, but this will blow thru rather than blow up _UNLESS_ the cat is hot.

One of the real problems is the timing belt, when you dump the cluch you shock load the timing belt, and this could lead to premature breakage.
Will Munns


Valid timing belt issue to one side for now...

Surely all the emmissions gubbins will stop most/all nasties from going down the exhaust and into the cat? If it were the case that neat fuel always got ot the cat on startup, then all the cats would break.
Thus, "friend" is talking rubbish.

My guess is it's a bad idea to bump start new cars as you say Bob, but if you do the worst it'll do is degrade the performance of your cat a bit. I think.

P.
Paul Nothard

>Surely all the emmissions gubbins...
Emmissions gubbins? I think you'll find the cat IS the emmissions gubbins, and the only other thing in the way is the exaust manifold!
Will Munns

I agree with Will - bump starting is OK if the cat is stone cold; the petrol will then vapourize before it does any damage.
Steve

I dont see what the difference it should make if you turn the engine over using the starter motor or the roadwheels via the gearbox. Either way, you turn the crankshaft, and I dont see how you could tell at the Cat which method was used.
Russell Parslow


Charcoal cannister?
Not quite sure really. :)

Matters not... as I've bump started my 'F a few times and it's still passed its mot. <grin>

P.
Paul Nothard

Charcoal canister is between the fuel tank (vent only!) and the inlet manifold.
Will Munns

Cheers guys....I'll still tell him he's wrong though (cos' I'll never admit I'm wrong!)
Bob Millar

Ah. Makes sense Will.

P.
Paul Nothard

This thread was discussed on 20/04/2004

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