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[mka306]

Assuming that you haven't a) topped up with diesel or b) bought some shit fuel Supermarket perchance?

If the coil pack/plug checks prove inconclusive, drain the tank, refill with Shell V power and throw in two cans of Wynns injector cleaner. Then give the car a good thrashing... aim for sub 20mpg and repeat but drive normally for the second tank

No I most definitely did not use any diesel, haven't owned a diesel for some years, I do use Tesco petrol station but I don't believe the £20 of fuel I put in for the first time since owning the car will cause this issue.

I have two new coil packs coming tomorrow so I will replace them and I will change the plug on no.5 just to be on the safe side but one thing my neighbour said was when I pulled away the day the miss fire happened he said the fumes smelt very rich as if it was over fuelling, what would cause over fuelling??

[Steve B]

Assuming that you haven't a) topped up with diesel or b) bought some shit fuel Supermarket perchance?

If the coil pack/plug checks prove inconclusive, drain the tank, refill with Shell V power and throw in two cans of Wynns injector cleaner. Then give the car a good thrashing... aim for sub 20mpg and repeat but drive normally for the second tank

No I most definitely did not use any diesel, haven't owned a diesel for some years, I do use Tesco petrol station but I don't believe the £20 of fuel I put in for the first time since owning the car will cause this issue.

I have two new coil packs coming tomorrow so I will replace them and I will change the plug on no.5 just to be on the safe side but one thing my neighbour said was when I pulled away the day the miss fire happened he said the fumes smelt very rich as if it was over fuelling, what would cause over fuelling??

Just swap over the 1,3,5 coil pack for now. You have no problem on the other bank... deal with the 305 code first 

[05omegav6]

V6 Omegas ALWAYS overfuel when cold, so don't fret that too much besides, if one cylinder isn't firing properly, then there's a chance that unburnt fuel could enter the exhaust, although iirc, the ecu shuts down the relevant injector

As for only buying £20 of Tesco fuel, if that was merely to top off, then in percentage terms it isn't a big deal, and should clear through quickly enough... but if it was below half a tank then potentially half your fuel could be bad, especially if it was from the dregs of their tank

Why do half a job though? Change all the plugs whilst you're at it

[Migv6 le Frog Fan]

Assuming that you haven't a) topped up with diesel or b) bought some shit fuel Supermarket perchance?

If the coil pack/plug checks prove inconclusive, drain the tank, refill with Shell V power and throw in two cans of Wynns injector cleaner. Then give the car a good thrashing... aim for sub 20mpg and repeat but drive normally for the second tank

I would agree with this. If the car ran fine before putting the fuel in and was rough as a hedgehogs arse shortly after, then it would point to dodgy fuel to me.
I wouldn't throw new parts at the problem until this has been investigated.

[mka306]

V6 Omegas ALWAYS overfuel when cold, so don't fret that too much besides, if one cylinder isn't firing properly, then there's a chance that unburnt fuel could enter the exhaust, although iirc, the ecu shuts down the relevant injector

As for only buying £20 of Tesco fuel, if that was merely to top off, then in percentage terms it isn't a big deal, and should clear through quickly enough... but if it was below half a tank then potentially half your fuel could be bad, especially if it was from the dregs of their tank

Why do half a job though? Change all the plugs whilst you're at it

I'm only replacing plug 5 because there all brand new plugs, I changed them about a month ago and haven't driven on the new plugs until yesterday. I will fill the tank with shell v power as adviced and hopefully the issue will be resolved.

So far all your help has been great so what ever happens I'd just like to say a big thank you to you all for the useful info. I will update you all tomorrow hopefully with good news.

[mka306]

Ok the engine is back together with both coil packs replaced and the no.5 spark plug replaced, started her up and job done, that lovely v6 roar is back. So thank you all for your help it was priceless.

Then I took her out for a spin and one thing I did notice which was a tad annoying was when I was driving at 30mph the revs wouldn't sit still, they kept pulsing from just over 1k rpm up to 1500 rpm, any ideas why it does this or is it an automatic thing? When driving through the gear it was no problem but when in a gear and driving at a set speed it started to happen, I did give her a good blast and that didn't seem to work either??

[Diamond Black Geezer]

Yup, mine stinks of petrol at first, to the point I thought I had a fuel leak, but no.

Odd engine behaviour though. I had a similar occurrence, and it was down to a bad seal between Throttle body and the plenum, and a badly adjusted throttle body screw. There was also a small air leak elsewhere. Lots of engine work had happened on mine, which was then laid up for a period of years, so my wavering idle and roughness was down to multiple issues (plus poor coilpack wiring, which was causing misfiring)

Given you've done a fair bit of work yourself, which presumably includes plenum removal, I'd be looking for air leaks. 

[mka306]

Yup, mine stinks of petrol at first, to the point I thought I had a fuel leak, but no.

Odd engine behaviour though. I had a similar occurrence, and it was down to a bad seal between Throttle body and the plenum, and a badly adjusted throttle body screw. There was also a small air leak elsewhere. Lots of engine work had happened on mine, which was then laid up for a period of years, so my wavering idle and roughness was down to multiple issues (plus poor coilpack wiring, which was causing misfiring)

Given you've done a fair bit of work yourself, which presumably includes plenum removal, I'd be looking for air leaks. 

Sounds reasonable to me, I shall have a look for any air leaks.