Annoying Misfire I can’t find or fix

[kozyoncars]

Hey all,

I’m on the verge of parting ways with this car. Every garage i’ve been too have told me to give up or just put up with it and that includes Ford.

Currently its been to 4 garages and i’m still no nearer finding the issue. I’ve thrown quite a lot of money at it and i’m not any closer to fixing it.

So. The car has what i would call an “intermittent” misfire. What do i mean by Intermittent. Well it doesn’t happen on every drive of the car – probably every other drive.

When does it happen? Ordinarily on hard acceleration/under load, around the 4000rpm mark.

What does it feel like? Well it feels like a hesitation/stutter in the rev range accompanied with a backfire from the exhaust (like you get on LC from ignition pulling).

Has it thrown a CEL? No – no CEL at all
What have i done so far?

So currently I have done the following either myself or via the aforementioned garages/

4 x Spark Plugs

4 x Coil Packs
2 x Map Sensors

1 x Intake Air Temp sensor

1 x 02 sensor

Misfire still present.

No codes being shown on Forscan or other computers. Ford aren’t interested unless it throws a CEL and other garages are of the opinion to just live with it or tear down engine. Which seems excessive.

Has anyone had this problem before and what did it end up being and how was it rectified? To say this car has been troublesome is an understatement. One specialist advised “if you’d have asked me before buying the car I would have told you to steer well clear of the Mk3 RS” and that is a very well known specialist and a guy i’ve dealt with for years – its a shame Ford did such a crappy job of putting these cars together. I am well and trully fed up and considering selling it as is for a big loss.

[bobcat]

Change the fuel filter 🙂👍

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Honorary Member

 

[kozyoncars]

I have also done that sorry knew something I missed out. Lol

[kozyoncars]

I guess your point on fuel is going to be next step.

 

Injectors/HPFP/FP sensor ??

[coastliner]

So annoying when you trust the experts and they spend your money swapping numerous parts, my view would be to check all earthing points especially as its intermittent and you have swapped out all the obvious parts eg coil packs

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Coastliner

[71-bda]

are you on the std map? ive had lots of ‘pauses’ when ive gone to open it up, like it just thinks for a split second what it wants to set the ignition timing at etc etc, then off it shoots, think its also happened when flat out in a gear, change up and whack the throttle open and again it just ‘waits’ a split second before applying power, I’m sure thats a safety measure to avoid overboost situation.

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No nothing.

No Mods. No rockers. Just a chunky knob, thats now been replaced by an RS knob innit.

No tackiness.

Std as Ford intended, but with a space saver wheel and jack and nuts and wheel brace. oh.. and flaps, a man has got to have flaps.

Innit?

 

[kozyoncars]

It’s a m375 pack so yes mapped.

The car and only developed the issue in April of this year. Drove perfectly till then. Randomly whilst on the m’way. It did it twice. Pulled over. Inspected what I could. Nothing to see. Drove fine for a week. Did it again. Which led to the first trip to Ford and then purchase of the sparks and coils.

Sparks were pre gapped but I checked against the ones in the car and they were the same. They are a step colder.

It’s progressively gotten worse. Now does it every other drive as I say but still intermittent. I would only say it does it more when the car is nice and hot. But it’s certainly not a normal hesitation. As I say the car jerks and backfires like a rolling anti-lag ignition cut. It’s not like a pause.

Just wish i could get it diagnosed.

I’ve not checked Earth’s. I’ll find them. Check them. Clean them and refit.

[coastliner]

There are some earths under the front carpet passengers side I think.

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Coastliner

[kozyoncars]

I found and cleaned up the engine bay ones. I’ll take a look at the inner ones… Though it’s a bit of a hassle getting the interior out. It’s frustrating if it is an earth can’t see why it would just start being an issue.

I’m leaning towards HPFP or Injectors at the moment.

Then I’m in the territory of engine tear down 😭

[71-bda]

usual suspects, intercooler blanking plate, fuel tank evap valve, fuel pump, then maybe pop the plugs out and scope the bores/tops of pistons

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No nothing.

No Mods. No rockers. Just a chunky knob, thats now been replaced by an RS knob innit.

No tackiness.

Std as Ford intended, but with a space saver wheel and jack and nuts and wheel brace. oh.. and flaps, a man has got to have flaps.

Innit?

 

[kozyoncars]

I lost the blanking plate only a few weeks ago. Just disintegrated. But the misfire was present before and since.

I’ve not heard of the fuel tank evap valve. Haven’t come across that in my research. I’ll have a look.

Then I’m on the same page…. Fuel pump and pistons.

[tonys]

I would replace the blanking plate anyway thus avoiding any internal condensation on that hot side of the IC potentially being drawn up into the inlet manifold. My understating is that is why Ford Engineers put it there! Check you have the necessary hardware for the M375 map. It came as standard on the FPM375 upgrade kit which included the upgraded recirculating valve and crossover air intake pipe. Good luck.

[kozyoncars]

Hi thanks everyone who’s responded thus far.

I do have the associated hardware as it was receipted and noted on the install certificate I have from mountune. Though that isn’t too day the recirc is working properly – I can hear it though most days through the intake (which I have swapped for the stage 3 Airtek one).

As an aside. On the point of the blanking plate. I’ve had turbo cars with big power and associated intercooler upgrades from Impreza to RS’s of several brands. I’ve never heard of condensation on an intercooler being an issue. I mean on certain Subaru cars I’ve had. They had IC water spray as standard… So essentially the same effect I would imagine. What makes the Ford different or is that a can of worms I should just leave alone?

[kozyoncars]

UPDATE –

I decided to strip everything back that had previously been done and refit – in doing so, took a look at the plugs and they didn’t look good despite being new – they were gapped as i had checked them. I replaced them with OEM ford plugs rather than the ngk that i had put in there and the misfire went away. So it could be all those sensor changes were for nothing. The car has of course since developed a further issue. Which i will post separately about.I stick by my original statement – these cars are not made very well lol

 

 

[pezzar666]

I had bad misfire under load and replaced the iridium plugs I had with an old set of ruthenium’s I had in my toolbox and the misfire was cured, since out a new set of ruthenium’s in

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