Odd, single cylinder misfire only at lowest idle

[Lunchietey]

About to turbo my ba wagon but making sure everything is sweet before I do it.

 

Have replaced plugs and coils with genuine, is on about the 6th tank of 98 with 2 bottles of injector cleaner so far, new filters all around etc. New TPS, new O2 sensor also fitted.

 

Car runs great at all times EXCEPT at a stop in drive with AC on when it idles right down between the AC kicking in and out. Gets a DEFINITE and constant miss on one cylinder. No miss at any other time and pulls hard to redline.

 

Also throws a P0172 rich code. 

 

The miss is very steady so definitely one cylinder. Thud thud thud.... You get the idea.

 

Where to next?!

Edited 15/07/17 03:19 AM by Lunchietey

[Lunchietey]

No ideas?

[k31th]

have you confirmed which cylinder is doing it? unplug the coil/plug you think is doing it and see if the cadence of the miss changes. If it doesn't change then you can check if the coil is actually sparking while unplugged from the spark plug. If it's not, then it's either a wiring or PCM coil driver. If it is, then check the spark plug connection to ensure it's correctly sparking in the cylinder itself.

[Lunchietey]

No haven't confirmed which cylinder. All plugs and coils are new. When initially fitted 1000km ago they were all perfect, no misfiring at all but it has slowly gotten worse.

 

Will pull them all as soon as I get time(bloody nightshifts :( )

[Lunchietey]

Oh and it doesn't misfire at any time except at lowest idle. Any increase in revs at all or any load or rpm it's perfectly smooth.

[Ralph Wiggum]

Is it a miss you can hear at the tail pipe or feel through the steering wheel? 

 

If the later, have a good look at your engine mounts. 

[Lunchietey]

Well I have been at work the last few nights and have driven my other cars so took the wagon to Woolies tonight. Missing like a bitch now and even cruising at 55kmhr I can feel it. Hmm guess tomorrow I will be pulling coils (an probably plugs) to see if I can suss it out.

 

Strange because the plugs/coils(genuine ford coils and NGK plugs) have only been in for maybe 1 or two tanks of 98 and it is getting worse again like before I did the plugs coils BUT it was the other way around before. Used to idle fine but miss under load.

 

Will report back tomorrow after pulling all of the plugs/coils. Will thoroughly clean the coil connectors etc while I'm there.

 

I don't think it's the mounts but will get the missus to give it a rev in D on the driveway to torque the motor up and check. It's a very rythmic miss, to me it definitely feels like one(or more) cylinders misses consistently at low revs and very light throttle now.

 

I'm hoping it's something stupid like one of the little rubbers under the coil cover fell out without me noticing and the coil has moved a touch or something.

Edited 18/07/17 11:58 AM by Lunchietey

[Ralph Wiggum]

Vaccum leaks

[Lunchietey]

DEFINITELY not mounts, can hear the doof doof doof of the miss from the exhaust. Couldn't easily see a vacuum leak(but that doesn't mean much) as all hoses etc look in vgc. Could be intake manifold leak but that doesn't explain the rich running. Pulling coils right now 

[Lunchietey]

All plugs look about the same, EXCEPT rear plug has a slightly darker look to it.

 

Seems a common issue on BAs is dirty injectors from dirt in the fuel rail collecting at the rear most injectors and in the reg. 

 

Seeing as injectors and reg are being replaced soon anyway for boost, might just leave it as is until the injectors and reg are changed and give it a flush at the time. Apart from a sh*tty idle it drives well.