Ramdon Misfire

Hi

I have 2004 V8 which has developed an intermittent fault, it starts a random misfire, normally when cold but lately also happens when warm. I have changed all 6 spark plugs, leads both coil packs and fuse box. My local garage have run out of ideas and other suggestions where to look.

rodneydavies said:

Hi

I have 2004 V8 which has developed an intermittent fault, it starts a random misfire, normally when cold but lately also happens when warm. I have changed all 6 spark plugs, leads both coil packs and fuse box. My local garage have run out of ideas and other suggestions where to look.

Click to expand...

I'm hoping you mean all eight plugs !!

slipped liner or h/g failure.was any 1 of the plugs you removed appear to look brand new compared to the others

Are these V8s fuel injected? If so, then start checking injectors and their wiring. Perhaps have the ignition timing checked too.

Diff.

rodneydavies said:

Hi

I have 2004 V8 which has developed an intermittent fault, it starts a random misfire, normally when cold but lately also happens when warm. I have changed all 6 spark plugs, leads both coil packs and fuse box. My local garage have run out of ideas and other suggestions where to look.

Click to expand...

but that garage doesnt have a tester?...to read some live data or fault codes?,... cos that's the way to do things unless you start to replace bits based on luck or suspicions... i hope they didnt replace just 6 plugs for you

sorry i mean't 8 plugs, yes local garage have put on tester and the misfire can occur on any of the clinders and it changes. So on Monday 1 and 8 will misfire and tuesday 2 and 5 so its completely random. It first occured when temp was very cold below zero c but when engine had warmed up went away, but now happening mainly when cold (but normal morning temps here in Devon) but can also happen when if engine is warmed up. If i floor it normally get better.?
Thanks in advance for your suggestions as i'm and the garage are at a loss

Hello, I have posted same problem in V-8 section. Will let you know when I get to the bottom of it.

water is settling in a cylinder(or 2) overnight,when you start it in the morning the plug(s) is wet so wont fire,clears when run for a minuite or so.can also do this underload,as ive prev stated its most prob h/g or liner issues ive had this on 2 p38s previously.put a camera down plug holes & check for steam cleaning of pistons/plugs will be a give away once removed & inspected

that sounds expensive, are there any ways of testing for this other than stripping the engine down and removing the heads ?

wil2813 said:

water is settling in a cylinder(or 2) overnight,when you start it in the morning the plug(s) is wet so wont fire,clears when run for a minuite or so.can also do this underload,as ive prev stated its most prob h/g or liner issues ive had this on 2 p38s previously.put a camera down plug holes & check for steam cleaning of pistons/plugs will be a give away once removed & inspected

Click to expand...

That if the OP is losing coolant,he's not mentioned that he is.

i have put some additional coolant in but very miniual approx mug full in last 3 months.
Would a compression test prove this one way to another ?

HenryD said:

That if the OP is losing coolant,he's not mentioned that he is.

Click to expand...

doesn't take a lot of coolant loss to achive this,he prob wouldn't notice, maybe 1/2 pint a week if that(if used everyday regular),it will eventually get worse and turn into h20 alcoholic

what you say makes sense but i have had these issues since Feb and no noticeable loss of coolant.
Would a compression test prove this one way or another ?

as he said though the plug only needs to be damp for it not to fire up

compression test should be up about 170psi I think? You may be very lucky and just have a hairline crack that only lets in a dribble of water now and then causing the plug to get damp and stop it firing