mis firing v8 yes i know. last update

[gtomo2]

Right my disco 3.5 v8 efi is mis firing on one cyl. have changed dissy, ht leads, checked and ajusted timing etc. its mis fires on lpg as well as petrol so its not a injector as gas is feed in from the air intake. when i take the plug leads off the plug with the engine running you can hear the spark jump from the end of the lead to the plug on all 8 cyls. so now me wondering has anyone had a problem before were the spark plug is shorting out on the engine block before as i am thinking this could be the only thing left it can be. its missing on the same cyl all the time. Or has anybody got another ideas about what it could be
thanks

[Thrasher]

Have you tried switching the plugs over? That would tell you if it was the plug..and also, have you got the plug wires laid out properly......it's a bit on an art....

[gtomo2]

Yea plug leads are as pre book i know they are ok as it took me ages to make sure they were not touching anything or each other. will try and swop plugs around and see if the mis fire moves. thanks

[Eeyore]

Is the misfire continuous, or does it seemingly come and go at inoppotune moments? This could be a big pointer to your woes.  :-k

Cheers
 8)
Eeyore

[gtomo2]

its constant and sounds like the same cyl just cant find it

[Eeyore]

Hmm, shift the plugs about as you suggest and check the condition of each it too - this should tell us if it's trying to run lean, rich, drowned in fuel, falling to pieces etc. All usefull stuff.

Ok, we know engines need four things to make 'em fire: fuel, spark, compression and air. If we can eliminate each one, we could find an answer. Or not........ <ahem>

If it's failing to fire on gas as well as petrol I think we can count injectors out. So as you say check the spark plug. If that seems to be working, it might be an induction problem. This might point to worn / gnarled lifters or cams for the cylinder, causing a lack of air or air/lpg depending on running conditions (which will stop it firing - there is a fairly tight tolerance on the air/fuel mixture). If that can be eliminated then it's time to look at a compression test to see if it's bleeding out somewhere.

Is it seeming to burn oil?

If it was slightly more intermittant, I would have said change to a better oil. But it isn't, so I won't.  

Hope some of this helps!

cheers
 8)
Eeyore

[gtomo2]

Thanks for that eeyore. will go back out in to the thick fog and see if i can find my car first. i know i left it in the drive but i cant see any further than the outside of the window were did this fog come from or have my cataracks? come away  :roll:  :(bigshock):

[dazzawhipple]

might be a sticky valve

As its been said move the spark plugs around


Darren

[Eeyore]

might be a sticky valve

Absolutely! Should have added that one to the induction list. Well spotted, that man.  

Should be spottable with the rocker off.

cheers
 8)
Eeyore
(also looking for his wagon, in the carpark, in the fog!)

[karlo]

Graeme, I have a doofer you put between the lead and plug and you can see it sparking works better in the dark though, only got the one so you'll have to do it one at a time!

[gtomo2]

might be a sticky valve

Absolutely! Should have added that one to the induction list. Well spotted, that man.  

Should be spottable with the rocker off.

cheers
 8)
Eeyore
(also looking for his wagon, in the carpark, in the fog!)

Knowing my luck it will be a sticking valve and it will be on the side that has all the air intake etc on not the side thats easy to get at.

Karlo, Thanks for that will give you a shout if i need it
Thanks

[hairyasswelder]

Graeme, I have a doofer you put between the lead and plug and you can see it sparking works better in the dark though, only got the one so you'll have to do it one at a time!

I got 4 of them so one bank at a time, only a few quid from draper stockist  :D

Steve

[gtomo2]

ok just been out to her now and took the spark plugs out one at a time and found one plug covered in unburnt fuel. so swop it over for another one i had and tested the plug against the eninge and found that when the plug is a short distance from the engine you get a spark jumping the gap as it should but  when you touch the threaded part of the spark plug against the engine no spark. so one broken spark plug just never know one to do that before. must be a broken core nside it. but is sounds like its back on all clys now. just fingers crossed and wait for the next fault/ thing to fall off :roll:  ant land rovers brill

[gtomo2]

Just got back for the lpg test station to v8 was still not right you could feel it runing uneven so he checked the timing and found the timing marks i used were not the correct one i used the cut out in the counter wight :roll: so when he checked it we found instead of it been 12 btdc it was.............................................................................. 42 btdc. so dissy off repostioned and all is well in the world of my v8 and me one very happy bunnie :(biggrin):  :(biggrin):  :(biggrin):

[Eeyore]

As long as it's sorted now. Sweet!

cheers
 8)
Eeyore

[gtomo2]

Yea and thanks everyone for your help. much apprecated.