Hi all.

My car is a '97 fiesta mk4 1.25 and its had a minor misfire for a while now.
It goes through the rev range fine, and I have no problems, other than when the car is sat idling, it shakes / vibrates, and the engine doesn't purr, it was quite rough.
Yesterday, I did somethings to try and fix it, first changed the fuel filter, then cleaned the MAF with some brake cleaner, then sprayed a little in the idle control valve, then I did a compression test and replaced the spark plugs.

This made it 10 times better, it purrs almost perfectly, but it still has a very slight misfire, I can feel the engine vibrating very slightly, Like it has when I've had the misfire, and now I don't know what else to do.

I need to test for air leaks, but apart from that, what else can I do?
I read the coil pack and leads are a common thing that needs to replace?

Also, when ever I turn off the engine, from the exhaust, it sounds as though there is alot of air being pushed out, what could that be?

Cheers, Jason

 

As you say the coil pack is most likely faulty (Common problem).

Tbh a misfire will have totally different symptoms to an air leak.

What you can do is remove each lead in turn, if there is no change then this is the faulty cylinder (It's said you shouldn't do this with modern coil pack systems) so you could remove one lead at a time then start the car and feel for the difference as Ford would say .

If you do it with the engine running be sure to use insulated pliers, else the current will end up going through you!

Martin

 

Thanks for your reply.

Would stopping one cylinder from firing damage the engine in any way?

Cheers, Jason

 

Also, Im thinking about changing the ignition coil.
I've seen some cheap ones for Ł15 which im staying away from, but I've also seen some around Ł40 and I've just found a genuine ford one for Ł100, Do I need to spend that much or would the Ł40 one suffice?

 

The problem seems to have come back and gotten worse, only when idling.
When I start my car from cold, it idles at around 1300rpm for a couple of mins, and the engine purrs out of the exhaust, when it gets down to normal idling speed it starts the vibrating, and blowing out the exhaust, (that's what it sounds like).

I've just ordered some new HT leads to see if that will fix it, if not, I'll replace the ignition coil, is there anything else to check?

Cheers.

 

I don't know what else to do to fix this misfire.

I have bought new spark plugs, HT Leads, Ignition Coil, Cleaned the MAF, cleaned the idle control valve, and I still have the misfire.

What else could be causing this?

Jason

 

Have you identified what cylinder(s) are misfiring?

If you have an exhaust leak this could also cause problems as the extra air in the exhaust will be detected by the lambda, this would also cause it to use more fuel.

Martin

 

I had a new exhaust fitted around 6 months ago because the back box burnt a hole through the top and the middle section wasnt very secure.
When I switch off the engine, it sounds as though its blowing air out the exhaust.

I'm a little weiry about starting the car with only 3 leads connected, its not going to damage the engine is it? What happened when I find the misfiring cylinder(s)?

THanks.

Jason

 

No it will be fine, after all the problem will be no worse then what you have, i.e. misfiring, thats the whole point as you are playing a "game of spot the difference", the one that dosen't make any difference is the one that is misfiring.

Martin

 

Thanks mate.

I shall have a look in the morning.

Jason

 

Well I took off each lead in turn, and started the engine, it was a struggle to start the engine each time, I had to give a bit of throttle to get it going, it was very rough each time I took a lead off and let it idle, it done the exact same thing, sounded the same, idled the same, what can it be?

Jason

 

If there was no difference then you have some ignition on the cylinders, but it could be intermittent, so is it misfiring all the time or only on occasions?

Have you fitted Bosch plugs?

Martin

 

I notice it only when Idling, the car / engine just vibrates and shakes the whole car. It does it regardless of weather the engine is cold or warm.

Also, I have problems starting the engine when its warm, It starts but revs at around 500rpm before dieing, I can give it a bit of gas it is completely fine after that.

No, I haven't fitted bosch plugs, they are NGK, should I have fitted bosch plugs?

Jason

 

Are you sure it's not an air leak?

This could cause the low idle which is what is making it shake, idle should be at least 700 RPM + when at running temperature.

No NGK are good, I just remember an ex member on here saying that Zetec's don't like Bosch plugs.

Martin

 

Thats the last thing to check for I think.
I've read somewhere about an air pipe under the air intake which is prone to splitting.

If I rev the car to about 1200rpm, it disapears altogether.

Thanks for your help mate, Ill check for air leaks and let you know how I get on.

Jason

 

No problem, yes that will be the PCV which is common on another Ford model, if you look under the inlet manifold look for a rubber hose, sparingly spraying WD40 around the inlet area with the engine running can help to find an air leak, any change in engine speed when you do so identifies where the leak is.

Martin

 

I will check that out, thanks for your help mate

Jason

 

I tried spraying WD40 around the valve, along the pipe, around the intake manifold and nothing.
When I turn off the engine, there is what sounds to be a rush of air out the exhaust, could a leak in the exhaust system cause this? I had a new exaust and mid section fitted about 6 months ago but I had this problem still before then.

Jason

 

I'm starting to think its not a misfire, I've just been reading at it seems as though it could be the crankshaft pulley? Vibrating only at idle.

Cars getting close to 98k miles.

Jason

 

Still fighting with this.
Looking for the EGR valve and am unsure weather my car has one or not, as I cant find it anywhere.

Any ideas where it is located, if I have one?

Cheers

 

Another update.

Today, I replaced my air filter, cleaned the ICV, the MAF, Throttle body, and as far into the air intake I could, using brake cleaner.
The problem of a misfire on idle still occurred but didnt seem as bad.
So, tonight, went to pick the mrs up from work, sat outside her house for about 20 mins chatting, the engine is slowly heating up, so we get out, I take her to her door and I hear the fan kicking in, (i left the engine running), I go back and listen to the exhaust, and the engine is purring almost perfectly, I sat in the car and I could feel very minor vibrations through the gearstick & steering wheel, not very noticable, by the time I have driven home, and the engine has cooled even more, I get out and have another listen to the exhaust, and its chuffing / vibrating / misfiring again.

So it seems that when the engine is very warm, it doesn't misfire?
Any ideas on what could cause that?

 

I also scanned the OBD and didnt find any faults.

 

Cts
Cylinder head temp sensor

Had the same thing on mine

 

Is it easy enough to replace?
And where did you get one from?

Cheers

 

Is there such a thing?
I've just searched all over the net and couldn't find anything for a fiesta, and there is no mention of it in the haynes manual?

 

I replaced the idle control valve, started up and straight away the engine was purring away nicely, now after going for a drive, its back to its old self again.

Don't have any idea what else it can be :/