Misfiring cylinder one

[Avante]

Cleaned map sensor with brake cleaner indirectly, ensured all 4 pipes to inlet are clag free, let engine run for 5-10 minutes idled from cool, seemed to run perfectly fine until the dreaded limp mode kicked in (no engine management light or codes this time), the rattling noise I've described before returned, and the engine seemed a whole lot louder and bassier while in so called limp mode. But apart from that, it seems to idle more fluently now instead of jumping between say 850 and 950 rpm, sits at a smooth 900 when warm.

[Avante]

https://vid.me/7IEu Edited 7 July, 2015 by Avante

[Breezy_Pete]

Weird 'crackle' noise at the start of each rev-up.

?

Dunno what that might be.

[Avante]

Sounds expensive :(

[Breezy_Pete]

Not necessarily.

Does it only make that noise when in 'limp mode' or all the time?

If there's no fault lights or codes, how do you know this is 'limp mode'? Maybe it's 'one cylinder shut down due to misfiring' mode? If there's a difference. Drive it around a bit and I'm sure some lights and codes will be forthcoming.

[Avante]

Correct it only does it in limp mode or when it appears a cylinder is misfiring, the engine shakes more, it sounds bassier, acceleration lag, and pulls very slowly as opposed to usual. The only code that persist to show is cylinder one misfire, I've had no other engine fault codes.

[Breezy_Pete]

Have you had a damn good look at the wiring going to coilpack no.1?

On my Polo there's a suspicious looking bit of heatshrink over one of the wires in that loom, probably indicating a prior repair.

 

(I think) Once the ECU has logged a certain number of misfires on any particular cylinder  it will stop fuelling that cylinder to reduce emissions impact of the fault, so your engine is running on three, imbalanced and generally unhappy thereafter.

[Avante]

Ive had a brief look, can't see any exposed cables but I can't really tell without a multimeter test kit, also I wouldn't know where to stick the other probe?

[Breezy_Pete]

Might have to unwrap the loom a bit and feel for any bits where a wire suddenly becomes weaker/more flexible locally, indicating snapped strands inside the (possibly cracked) plastic insulation.

I'll have a look where you might be able to trace them to, but I think at least two of the four go direct to the engine ECU which makes them awkward to buzz-out end-to-end. Wouldn't tell you much anyway if you've got a wire that hasn't completely failed yet. 

 

If you had a wire that was down to its last intact strand or two, it might be that it's OK cold, but just too resistive to carry the necessary current once warm.

 

Edit: only one wire from each coilpack connector goes to the ecu, the thinnest one from coilpack connector pin 4; presumably also the most fragile. For cyl 1 it goes to ECU PIN 102, should be green/brown.

Pins 1 & 2 both go (eventually) to earth/batt neg.

Pin 3 is ignition live (12V nominal) from fuse 52.

[Avante]

Could be a case, surely a continuity test would check the resistance, if the cable is more damaged itd show up on the test wouldn't it?

I really do appreciate your guys time and patience.

[Breezy_Pete]

Maybe, but even if you're down to the very last strand at one point on the wire run, the resistance measured by a multimeter will still show as a very low value, because the current that the meter uses to check it is tiny, too small to heat up that one strand and make it 'show up' as resistive. 

 

Helps that I'm off sick in bed and only 50% occupied by the tennis.

[Avante]

Maybe, but even if you're down to the very last strand at one point on the wire run, the resistance measured by a multimeter will still show as a very low value, because the current that the meter uses to check it is tiny, too small to heat up that one strand and make it 'show up' as resistive.

Helps that I'm off sick in bed and only 50% occupied by the tennis.

I start work at 4 until 10/11 tonight, so I've got tomorrow morning until 4 again to do as much as I can. May get it taken for an MOT, but with the persistent misfiring I don't know if they'll be able to accurately tell me what it's failing on. Especially regards to emissions etc.

[Breezy_Pete]

I wouldn't think it's worth MOT'ing right now, as it has to fail, but I guess you're expecting that anyway with balljoint issue etc.

 

Tennis is getting exciting now.

[Avante]

Indeed but it may give me an insight to what else needs doing that I'm unaware of - its due this month and I'm getting worried about how expensive this is going to be. When I pulled up outside work I let it idle for a minute or two as I normally do when starting or stopping the engine, and it bogged once? Maybe just a single misfire, engine wasn't warm either was just hitting the 40/50 mark. I'm going to attempt to clean the injectors tomorrow providing I can gather enough information to feel confident enough to do it tomorrow. May go to TPS to get some o-rings as we know the 2nd one definitely needs replacing, is it a challenge to remove clean and replace these? Including the new rings, I don't want to take on a job I won't be able to complete and be left car-less.

[Breezy_Pete]

Judging by what you've achieved so far, I think you'll do it just fine.

 

Might be easiest to disconnect wiring conns and move loom out the way, then undo two bolts holding fuel rail, and pull all four injectors using the rail as a puller. Then release retaining clips and each injector from rail.  Best to pop the bonnet via the passenger door after an overnight sit, so that the fuel pump hasn't pressurised the system (which it does as you open driver's door).  Should be a less squirty experience that way.

 

Have rags to hand to mop up spillages.

[Avante]

My main concern is when it comes to pulling the injectors out. I can't imagine they sit in there loosly, and id rather not break them off into the engine head lol. Any advice on this?

Slow replies as of now, my shift begins now but I'll check back on my breaks to catch up

[Breezy_Pete]

Have a look at the pics in this listing. There's hardly anything of the injectors inserted into the manifold.

[Avante]

Oh yeah you're right, shouldn't be too tricky then. I'll let you know how it gets on tomorrow

Edit: Now I understand your confusion about me asking about pullers!

Edited 7 July, 2015 by Avante

[rum4mo]

A couple of comments - useful or not, first, injector removal, remember that this is a petrol engine with manifold injection, that means that very little effort should be needed to hold these injectors in place - so they should be able to be removed with very little effort. Second, you have said that the engine becomes rough/uneven only when heated up, one aspect of that is the water coolant temperature sensor being faulty - that has been suggested already, the other thing is that when it is heated up, the emissions control bits operate in closed loop, so maybe one of the Lambda sensors, B1 S1, is "not too good" but not duff enough to cause a fault to get logged - just thoughts moving around in my head - I think.

 

Oh bother, I'm taking too long to compose posts so end up repeating others! (sorry)

Edited 7 July, 2015 by rum4mo

[sepulchrave]

It's almost certainly the ECU shutting down the injector due to a detected misfire, the misfire itself will be caused by a coil pack, spark plug or the wiring loom.

[Avante]

Thanks rum4mo, I'll get around to sorting the coolant sensor after I've done engine flush, oil change, new filter and rad weld and new coolant. I'm still to learn the location of the lambda sensor and what it actually does. Appreciate you jotting these thoughts, how would I go about resetting those ECU values down to several misfires, as I have 4 new coil packs and 4 new spark plugs, loom seems fine too.

[sepulchrave]

I have 4 new coil packs and 4 new spark plugs, loom seems fine too.

 

Have you checked the new parts, it's quite easy to crack a brand new spark plug while fitting it as well, when you say the loom 'seems' fine, have you had the plug off the ECU, shorted the plug at the coil and tested for continuity while wiggling it?

[Avante]

I haven't I don't have access to a multi meter, I meant visually and I've felt along the wires for wear. I've checked the spark plugs and no cracks or damage.

[sepulchrave]

I haven't I don't have access to a multi meter, I meant visually and I've felt along the wires for wear. I've checked the spark plugs and no cracks or damage.

 

You don't need a multimeter, disconnect both ends of the loom from the coil packs and the ECU, use a paperclip to short the coilpack plug, use a wire to earth one ECU end temporarily, another wire to the other ECU end, hold a 12v bulb to the positive battery terminal and connect it with the wire while wiggling the loom to see if the bulb flickers at all.

[Avante]

Alright thanks. I'll have to look that up to find more information on it before I go pulling wires out of coil connectors.

Just been on the phone to TPS and its £40 for 8 o-rings for injectors, are you required to replace these when replacing any injectors, even the old ones?