Help with missfire

[multiskilled]

hi all
my c70 t5 me7 has devoleped a missfire it only happens when its up to normal temp and only if your trying to maintain a constant speed, if your accelarating it dosent do it although it may be holding back very slightley, it starts up fine, idles ok when cold but when hot sometimes idles eratic for about 20 secs then sorts itself out and is fine. ive changed the plugs and got a new coil pack and swapped it round on every cylinder but its made no diffrence, ive got no warning lights on and ive plugged a code reader in and no codes are logged. anyone got any ideas or had the same trouble ?

[JamesT5]

At the very worst it could be a valve problem but I doubt it. Have you tried changing your fuel filter? There's also a chance the fuel could be contaminated but again I think that unlikely.

If I think of anything else I'll let you know.

Regards

James

[multiskilled]

havent changed the feul filter where would i find it

[JamesT5]

havent changed the feul filter where would i find it

Not sure on the P1 based models but it's normally the same side as the fuel tank probably near the back wheel either behind or in front of it. If the fuel filter is blocked it can reduce fuel flow, it's just an idea to change it as it doesn't cost a lot and then you can rule it out if nothing else.

[V70 Graham]

havent changed the feul filter where would i find it

The fuel filter is located under the sill, drivers side, just forward of the rear tyre.

[multiskilled]

ok thanks i will give a go and see

[JamesT5]

ok thanks i will give a go and see

As I say, it's the cheapest option to try first if you're code reader is throwing nothing up on the screen.

[T5frankie]

could be lambda sensor, air flow meter, plugs or leads, vacuum leak

[JamesT5]

could be lambda sensor, air flow meter, plugs or leads, vacuum leak

I'd have thought they would have flagged up on the code reader, wouldn't they?

[T5frankie]

I'd have thought they would have flagged up on the code reader, wouldn't they?

depends on what code reader it is

[multiskilled]

wouldent they bring a light on the dash

[JamesT5]

wouldent they bring a light on the dash

Quite often yes.

[multiskilled]

im going to try and get a fuel filter tomorrow and change that as it seems the cheapest option, do i have to drain the fuel tank down first before i remove the filter

[T5frankie]

wouldent they bring a light on the dash

not always, a vac leak wouldnt

[multiskilled]

How would you check for a vac leak

[multiskilled]

Just been and had another fiddle and found that if you pull up on the inlet manifold lightly it idles erratic although there doesn't seem to be anything loose and if you push down it runs fine

[timbo]

Check all of your rubber Vac lines under the bonnet, they oftern perish and go crusty due to the high temps/old age, sometimes they look fine but give them a wiggle n feel their condition to make sure they're sound, one of mine had split where it fastened to the jubile clip, wouldnt have noticed by just looking at it but gave it a waggle and it just popped off. I dont have any pics but once you have a rummage about you'll be able to get youre hands on all of them.

[multiskilled]

Will do,had enough of it today,another sleepless night lays ahead

[JamesT5]

im going to try and get a fuel filter tomorrow and change that as it seems the cheapest option, do i have to drain the fuel tank down first before i remove the filter

No you don't, but watch your eyes because the fuel pressure in the system can cause a small amount to come out under pressure. You may need to 'crank' it a few times to get the fuel flowing again once you have the new filter on.

[T5frankie]

Just been and had another fiddle and found that if you pull up on the inlet manifold lightly it idles erratic although there doesn't seem to be anything loose and if you push down it runs fine

for one thing you shouldnt be able to move the inlet manifold at all, it maybe the vac line into the left side of the inlet

[smithson007]

Dodgy leads/plugs wouldnt throw a light on. A failing MAF doesnt always either. Try taking the MAF out and cleaning it see if tht helps they can cause all sorts of problems.
As for changing the fuel filter just let the pressure out the system from the valve on the side the fuel rail.
Again check all vac lines or boost hoses for splits.

[multiskilled]

shes all sorted out and running sweet as a nut, it was the fuel filter.
thank you all for your help espescialy james t5 spot on mate.
no more sleepless nights dreaming of etms etc thanks guys

[JamesT5]

shes all sorted out and running sweet as a nut, it was the fuel filter.
thank you all for your help espescialy james t5 spot on mate.
no more sleepless nights dreaming of etms etc thanks guys

No problem mate, I'm just glad to be able to help someone else out for a change, it's normally me asking others for help. I'm glad you've sorted it out anyway, if there's one thing I've learned from people on the forum it's often the simple things that are the problem. :beer: :B_thumb: