Misfire at idle - 1.4 16v BBZ

[isambard]

Hi all,

I have owned my 1.4 16v Fabia Estate for just over two years now and it has generally been very realiable. Over that time it has increased from 61k to 89k miles

Over the bank holiday weekend i drove it to Scotland and back on a 600 mile round trip, and the car drove beautifully, apart from one thing:

Every time i sat in crawling/stand still traffic, or waited at a junction for more than a few seconds the idle speed would drop, the car would shudder, and the engine management light would come on.

Each time i pulled over and read the fault code before clearing it and continuing without problem. The fault code every time was misfire (cylinder 3)

I have been reading around the forum and this looks like it could be a dirty EGR valve/pipe, but would this repeatedly cause cylinder 3 to misfire?

The car has pulled similar tricks in the past, but nowhere near as often. Every time it has been during hot weather (20 degrees plus)

 

Can anyone suggest the most likely culprit? Or should i continue down the EGR-valve route?

 

Many thanks

Isambard

 

PS The car has recent ignition coils and spark plugs so i don't think these are the problem

 

[sepulchrave]

Replace the coil pack on cylinder 3, they tend to break down when hot, EGR problem affect all cylinders at random leading to rough running and multiple codes.

 

Edit: New coil packs can be dodgy as well.

Edited 25 April, 2019 by sepulchrave

[isambard]

Hi Sepulchrave, thanks for your suggestion. Since you suggest the coil i should add a little more info: cylinder 3 has misfired two other times recently; once in Feb when SWMBO was driving, and the RAC replaced the ignition coil (with whatever brand they use) and then again in March, which i promptly replaced with a Bosche coil which i assumed would be a good quality one.

I didn't mention this before because both times the ignition coil was assumed to be faulty and replaced straight away, whereas over the weekend i simply reset the fault code and drove on with no problems at higher RPM (leading me to belive that the coil was not the problem).

Is it possible/likely that the cylinder would only misfire at low RPM if the coil was to blame? If so, what make do you think i should use?

Thanks

[sepulchrave]

Ok, maybe not the coil pack then, you should pull number 3 plug and check the colour and condition of the plug itself despite it being new.

[mikey362]

Could be a faulty injector, run some injector cleaner through and see if it helps.

 

if you swap the coil from another cylinder and the misfire is still on cylinder three. It is logical to assume that the coil is not the issue. Like wise with the spark plug, put on a different cylinder and if the fault remains on cylinder 3 that is not the issue.

Edited 25 April, 2019 by mikey362

[Breezy_Pete]

If you move cylinder 3's coilpack to cylinder 2 and cylinder 3's injector to cylinder 4 you could rule in/out both in one hit. (Tech1e tip IIRC).

 

As it's only happening in heatsoaky situations, it might be worth checking that your radiator fan(s) are working properly (does the car have A/C?).

Also, check that the airbox blend flap isn't stuck in the hot-only position.

Either or both might be exacerbating the situation.

 

[isambard]

Thanks a lot for the suggestions guys. I will do some experimenting on Saturday

 

I can swap the coils round no problem, but how do i swap the injectors? Is it simple?

 

1 hour ago, Wino said:

it might be worth checking that your radiator fan(s) are working properly (does the car have A/C?)

Now that you mention it, i have never heard the rad fans blowing; how would i check they are working? The car does indeed have AC, and it blows nice and cold

 

Thanks

[rum4mo]

If the AC is blowing nice and cold in hot weather then one fan must be working at least, the normal fan failure is the low speed on the main fan if you have 2 fans, that would normally show up as engine temperature rising a lot higher that normal then getting pulled back down - and repeating this, as opposed to just rising a bit higher and coming back down when stationary or moving slowly in warmer weather.

 

Sorry about the "lot" and "bit" terms for describing hotter indicated engine temperatures.

[isambard]

Thanks Rum, i'm sure the temperature needle wasn't climbing while thie problem was going on, so i will assume the fans are working ok for now and investigate the injector/coil/spark plug tomorrow

 

I'll report back

[Breezy_Pete]

To test fans just switch on A/C with temp set low and expect both to start up together after a short time (variable depending on engine bay and ambient temperature).

 

I've never actually changed an injector on this platform, but it probably isn't too tricky. Release any pressure via the Schrader valve at one end of fuel rail, release wiring connectors, probably a couple of retaining screws on the rail and some clips on the injectors??

See if Youtube has any guides.

[isambard]

Update as promised:

I have swapped the coil to cylinder 2, and the injector to cylinder 4 (pretty much exactly as you guessed Wino).

Nothing to report performance wise so far as it isn't sunny enough to trigger the issue!

I did however take a pic of some dodgy looking wiring leading to the coil on cylinder 3. Does this look like it could cause the issue? If so how easy would it be to replace?

[Breezy_Pete]

I have a vague memory of seeing similar on my car, so suspect that is a splice that's done during loom manufacture, rather than the 'dodgy fix' that it resembles at first glance.  Will have a look later, if I get a chance.

[isambard]

Does that rule it out then, or could it still be a weak point? No hot weather and sunshine forecast for the next few weeks to test it!

[Breezy_Pete]

Probably rules it out. Mine has exactly the same arrangement. 

Errm, just one thing though, that splice is on the way to coilpack no2, not no3. They're counted from cambelt end.

[isambard]

Oh! How stupid of me! However, coil 3 (the real number 3!) was still definitely replaced by the RAC in February; i have the rescue report and have just double checked it, so it has still failed very quickly if that is at fault.

That means that yesterday i still swapped the suspect coil for a bosche unit so should still learn something depending on whether the misfire reoccurs on cylinder 2 or 3. If it happens on cyl 3 again then i will try swapping the correct fuel injectors round!

Thanks for pointing it out

[TMB]

2 hours ago, Wino said:

Errm, just one thing though...

 

[Breezy_Pete]

No stupidity involved.

I didn't notice the discrepancy when I first looked at the pictures. It was only when I looked at my engine that it struck me.

[Xsr]

Coming to a halt at a stop light after driving with no issues, then Shuddering and throwing a check engine light warning also sound exactly like the symptoms of a dirty Mass air volume/flow sensor. But that would have thrown a P0101 code.

[sepulchrave]

1 hour ago, Xsr said:

Coming to a halt at a stop light after driving with no issues, then Shuddering and throwing a check engine light warning also sound exactly like the symptoms of a dirty Mass air volume/flow sensor. But that would have thrown a P0101 code.

 

Still no MAF on a 1.4 16V so it can't be that.

[LB123]

I have had two coils die on my BBZ engined Fab. Both times coil 3. That may be just coincidence. I now keep a spare coil to hand.

[Xsr]

18 hours ago, sepulchrave said:

 

Still no MAF on a 1.4 16V so it can't be that.

 

Correct. I meant the MAP sensor.

[isambard]

Thanks for the suggestion XSR; where is the MAP sensor located?

 

Update since latest post: not had any misfire engine codes come back yet, but the weather was warmer yesterday and the car was definitely idling rough

 

I'm sure it will happen again in the next few weeks!

[TMB]

3 hours ago, isambard said:

where is the MAP sensor located?

 

 

 

On the end of the intake manifold...

 

 

Edited 13 May, 2019 by TMB

[sepulchrave]

Rough idling and a MAP fault code suggests a vacuum leak rather than a problem with the actual sensor.

[Xsr]

 

7 hours ago, isambard said:

Thanks for the suggestion XSR; where is the MAP sensor located?

 

Its underneath this thing. Take off the hoses and remove a couple bolts. And you'll find it plugged into the intake manifold with 2 bolts. Can't miss it.

Just use some electrical contact cleaner to clean it

Edited 13 May, 2019 by Xsr