Breezy_Pete

I guess my day has been relatively OK after all...

I think it's high time I worked out how to get an upwards view inside these cylinders, especially no. 2. I know I could get the head off in very little time, but it'll take me ages to get it all back together, and I'll be so upset if - when I get in there - there isn't any sign of trouble that would justify the removal! If it wasn't for the silicone sealant everywhere, cam cover to head, timing cover to everything, sump to block and timing cover, it would be much less onerous.

Interesting thought, thanks. Would be easier, for sure.

Yeah, you're right on that. Trouble is, I'm really unconvinced that swapping in another coilpack is going to have helped, cos I've already swapped in different (spare) coilpacks into cylinders two and three, a few days ago, and left them in there. So that can't have been the issue before then, and now. Can't help thinking she'll have recurrence(s) of limp mode on the way back on Sunday, due to real fault (whatever the hell that is). I want to drive out to where she is* in my Polo, swap cars with her and come back in hers. She won't hear of it though cos she has breakdown cover, I don't. Plus it's no less likely to break down with me at the wheel, really. Just don't want her having the stress and anxiety. Already taught her that cycling the ignition may kick it out of limp mode/cylinder shutdown, at least temporarily. Aaaaaaaarghhh! *2.5 hrs away

@jd03 All mk1 Fabias have electrohydraulic PAS, so you don't have a steering pump driven by the engine. The pump is part of the module under the reservoir. This image may be useful to you:

No, 12V supply from blue/red on loom connector, but fuel pump relay needs to be on, so at least ignition on, not sure if that's enough.. Yes resistance from 3-5 of sensor connector, with it unplugged from loom. TBH, any fault here would generate a fault code, I'm near certain.

Here's the wiring: Z19 is the integrated heater in the sensor G39. Continuous 12V goes onto one end of it at sensor pin 5 (blue/red), PWM controlled ground connection from ECU pin 5 to sensor pin 3 (brown wire) to heat as required to get desired temperature. I seem to remember the little external resistor (rectangle between pins 1 and 2) is some sort of 'select on test' tuning thing fitted as it's tested in the sensor factory. Lives under that cover that fell off yours I think. Google will probably be able to tell you far more than I can about what the four thinner wires do. Some current is varied by the ECU to keep something static, and the oxygen content can be inferred from the size of that current, is about the extent of what I remember. Test instructions for heater resistance: - At ambient temperature the resistance of the heating element should be approx. 1...5 . The resistance increases considerably even if the temperature rises only slightly

You're not wrong. I wish I understood a hell of a lot more about how all this stuff works, in detail. I can tell you the wiring details shortly, and some test info. Not sure there's much you can do beyond measuring heater resistance at ambient temperature (from memory of reading about it).

Food for the 'Chuckle in your day' thread?

Different for wideband sensors.

There's a click together/pull apart connection just the engine-bay side of the firewall.

Rear washer water feed, I think. Could go through same hole. Make sure you put a fuse near the battery for any added wire - current rating as per what the wire is rated at. Fire-risk otherwise.

Its super-hot environment ought to be sufficient to keep it functionally clean. No particular reason to replace as a pair, but I would hesitate to suggest replacement at all without much better evidence. You should see specific fault codes related to misbehaviours, and having just falsely thought I'd fixed one of our cars by doing just this, I am extra-wary. Expensive things too, usually.

I think actually sep, these wideband sensors start doing their job within a very few seconds of start-up (that's what my logging suggests anyhow). The second sensor, after both cats, can compensate for duff/non-existent info from the first one, so will try to keep things on the straight and narrow as much as it can, which won't be enough for long in the complete absence of input from the first. After getting the lambda connection to stay put, try running it without the cover/air filter fitted and see if symptoms change, there's a common fault that leads to the engine only being fed pre-heated air, which isn't good at this time of the year. Is the weather quite hot where you are Martin?

I wonder...I've always assumed that the misfires that go with exhaust valve trouble are due to gas leakage during the combustion event, (why) would that cause misfiring?. But another possibility that's only just occurred to me is that the valve(s) is/aren't actually leaking much at all, but is staying so hot due to damage or just poor seating and consequent poor heat-conduction path into cylinder head; so it triggers pre-ignition?? Is that what really happens? Seems a bit 'out there' to me, but I have very little knowledge of the details of combustion cycles, and what goes wrong with them.

And that drive went OK, but I really doubt it was the coilpack. Back to believing it might be exhaust valve(s) after all. 🙄

Spoke too soon actually Lee. Bloody thing went into limp mode a couple of miles from destination. Cylinder 2 misfire code plus the precat lambda code. On the end of a whatsapp video chat she's just swapped out cyl 2 coilpack and is heading out for a short range test drive...

Radiator seal might fix the matrix leak, for now, so maybe worth a try. Does the oily film look pinkish if you wipe it away with a white tissue? I can't think what else it would be other than coolant, but a colour match would be good evidence.

I think if your car had an EGR valve, fuse 7 would be relevant to that. Gotta walk the dog, do some work etc. but I'll come back to this later. Are you sure the front oxygen sensor only has 4 wires, I'd expect 5? Are you in Germany or Oxford at the moment?

It seems like the answer to the thread title is no. What I should have asked was - is it time for a new pre-cat oxygen sensor? Replacing that seems to have restored correct function, according to a chirpy voice message I just got from its owner, on the road. Fitted and immediately took some logs yesterday, static and on a test drive. Will review the data later, but it felt better if not perfect straight away. Thanks for the suggestions and comments.

I still can't quite work out the function of that airbox hose. Is there a one-way valve in the airbox; to which it connects? Or a rather narrow orifice/jet?

So where isn't the grommet? At airbox end?

Might just be a VCDS quirk?

Could you take and post a photo of this? I'm not familiar with the breather arrangement on the automatic cars, so I'm not clear what exactly you mean, or what it does. That rings some alarm bells. Has the coolant temperature sensor ever been changed to your knowledge? Later versions of the BKY engine had the EGR valve deleted from the design for some reason. My recently acquired Polo has the same lack. Can't say I'm upset by the absence of something that seemed to cause a lot of problems on this engine family. That spark plug does look odd, but I can't remember anything except additives causing weird colourations? Which oil does it get?

Massive QA fail. Push for some sort of compensation (free brake fluid replacement and oil change?) as well as free replacement with correct part.