backfiring cause..

my 340s got a problem where if i back off the accellerator quickly (ie if i rev the engine then let it idle again) then whilst the engine revs are falling it sounds like the engine is backfiring - my guess is that the mixture is running too rich - am i right??

Hugh

Hi Hugh

Might be the mix but not necessarily.

I did notice on one of your posts in 300Mania that you`ve had some exhaust bits changed - an exhaust leak can cause it when air gets in and mixes with unburnt fuel. Did this start after the exhaust repair?

Can also be caused by ignition problems when an unburnt cylinder charge gets into the exhaust.

If it`s popping up through the carb rather than the exhaust could point to problems with an inlet valve. Might be sticking or need adjusting.(should be checked every 6000 miles on a 1.4 in any case)

Will

hi will

thanks for the tips - the exhaust front pipe was replaced yesterday but the problem was actually there before this - i thought that the exhaust fix might stop it but evidently not. i dont think its popping up thru the carb becuase with the filter off i cant see anything going on when the noise happens. its not much of an issue - it sounds a bit like a rally car :) i dont think its the mixture either cos i was playing with that earlier and adjusting it a long way either direction doesnt stop the pops, it just makes the idle rougher..

i did the valves last time i serviced the car, which is probably getting on to being 6000miles ago - not sure though, probably about time i did a service on it again :P

I'll see if it settles in a while..

incidentally - oil in the water - normally a sign the head gaskets gone isnt it? is there anything the garage might have done that caused it cos i've not noticed it ever before, but now theres a thin layer of gunk on the top of the coolant resovoir..

Hi Hugh

I`d keep an eye on the oil in the water and start looking out for other symptoms of the gasket going. They are a bit delicate on the 1.4 and I`ve to do a couple. Can`t think of anything the garage may have done

It may be that a valve is a bit sticky or not sealing well - a gasket change would be a good chance to sort this out. It`s not a difficult job to do as long as you follow the directions in the manual to avoid disturbing the liners

Will

what are the other symtoms? also, where'd i get something like a gasket from? i'm guessing places like halfords dont stock them :)

Don`t panic - it might be fine!!

Usual HG failure symptoms are:

* Oil in coolant

* Loads of tiny bubbles in coolant after a run

* Coolant in oil - mayo in filler cap or around dipstick

* Overheating

Any half way decent motor factors should be able to get one or your local Volvo dealer (£ ouch!)Get a complete head set with a new rocker cover and water pump gaskets, valve stem seals and exhaust/inlet manifold gaskets. I think I paid about £20 last time plus £45 to get the head skimmed.

Will

thanks again for your help :)

its definatly not overheating, and there's no mayo-like stuff in the oil compartments... dont really wanna spend a lot of money on the car as its done 181k, i just need to get it thru to 200k and then i'm gonna let it die :) does a leaking h/g actually cause any probs, other than overheating? i think i might take all the crap out of the coolant res (by unplugging the pipe below it) then top it up again, so i can monitor it.. i'm never too careful when i pore oil in (engine bay is crappy enough as it is), so peraps some of that spilt onto something vital.. i might have overfilled the oil last time i did it as well..

just found a gasket on gsf, its only £15 or so, aint too bad if it does need doing - guess i'll put it on my 'todo' list :)

hugh

ps. who are you on v3m?

Same user name on v3m: wjp01908