Misfiring cylinder one

[rum4mo]

I think that the idea is to just check the injector action/spray pattern as I'd think that they are either okay or duff and duff would mean "bin" - replace.  I seem to remember that over the past 10 or so years, these "mysterious" cylinder * misfiring, after all other checks had been done on coil/plug - the injector had been found to be faulty, not my experience luckily, just on reading many VAG forums, though it does seem that this is not a common issue.

 

Being a realistic home "mechanic", I have been waiting for this fault to "happen" to one of my VAG cars, but so far, so good. If it did happen, I would probably have made up one of these "injector tester" AFTER replacing the injector with a new VAG sourced one, then save the duff injector and the test kit in a very safe place for the future - or for someone to bin when I've GONE!

 

Edit:- remember the pressurised can of injector cleaner is, I think, just being used as a pressurised source of liquid to visually check the injection action and spray pattern, in the knowledge that this fluid will not damage the injector internals.

Edited 25 July, 2015 by rum4mo

[Breezy_Pete]

Cleaning out of any substances that may be interfering with good spray pattern and delivery rate were my goals, not just checking.  Whether there's really anything that builds up inside fuel injectors I'm not sure. Always thought petrol to be quite a good cleaner/solvent!  However, on at least one of these youtube vids, a guy with a slightly more elaborate set-up is collecting some distinctly murky looking cleaning fluid after passage through injectors.

 

Gonna have a go at the four from my Golf later, just for a giggle.  Almost 200k on the clock and AFAIK never had any cleaning of injectors, so should be a good candidate.

 

If there are any interesting results I'll try to get some pics

[Avante]

I believe it is the injector itself that is faulty, I've looked high and low for what wouldve damaged the insulation for the wires to the injector and can't find anything, so I've come to the conclusion in my own mind that the injector is faulty and caused this problem. Swapped it over two and problem "appears" to have moved - I believe it'll be pointless cleaning it and would be better off replacing it.

[Breezy_Pete]

Fair play mate. I did get my rig set up and tested on some spare injectors, but I'm not keen on it. No sign of anything murky in the emerging fluid, and a cracking headache afterwards. The latter may be coincidence, but carb cleaner vapour isn't good stuff to be breathing, even outdoors like I was.

 

 

I think 036906031L is the part number you'll be after; good selection on ebay if the new price is off-putting, including a new genuine one on best offer, and various used ones.

[sepulchrave]

Injectors simply don't get dirty like they used to, this is because fuel filters are better, the delivery pressure is higher and the pintle itself is 'self cleaning'. This information won't stop idiots from buying harmless but useless snake oils to clean them but hey-ho.

[Breezy_Pete]

I can't remember if OP has a multimeter, but a resistance measurement that was an 'odd one out' from the other three would be a handy condemnation of the injector that used to be number one cylinder's.  Dunno why I didn't think to suggest that check before*.  Same resistance doesn't clear it from suspicion completely though.

 

* There are fault codes for electrical issues with injectors, one of which, 16585, is very close visually to the 16685 one you've posted, did you save the scan? Sure that second 6 wasn't a 5?

[Avante]

I'm sure mate, 16685 is the code given. Swapped injectors and still 16685, so maybe it's the wiring and not the actual injector?

[Breezy_Pete]

I'd be compression testing the engine next, if it were mine.

 

You can easily check one of the wires though, with ignition on, the blue/white wire should have a nominal 12V relative to battery negative (which shouldn't go away if you waggle the wire in the vicinity of the connector). Edit: Just checked this on the diagrams, and you might need to be cranking the engine over before this 12V appears (not sure, haven't tried it myself).

The other wires for each injector will probably also be at about 12V with engine not running and plugs disconnected from injectors: compare what you get on all four of those wires (purple/brown, purple/green, purple/yellow and purple/blue for cylinders 1-4 respectively), waggling wires each time to try to reveal weaknesses.

 

May be best to do this when engine is fully up to temperature, as that's when you're having problems I think, isn't it? Also when wire insulation will be floppiest.

[Avante]

How would I test the voltage of each injector plug?

[Breezy_Pete]

I guess you don't have a multimeter then?

 

Something like this is what I had in mind:

 

 

Multimeter set to read Volts dc. Red probe on item under test, black one to engine metalwork.

 

Actually, measuring voltages turns out to be not a very good strategy, because the 12V on the blue/white wires is only present when the fuel pump is running. (At first turn on of ignition - for only a few seconds -, during cranking, and during running, so not ever-so easy to do on your own)

 

A better way might be to measure resistance - Ohms (Ω) - between the blue/white wire pin of one injector plug and the same colour wire on one of the others. They are all supposed to be connected together, so should read zero Ohms.

 

The other pins, which the purple/other colour wires go to, are wired straight to four separate pins at the ECU, which you may or may not be able to easily unplug the connector from.  Disconnect battery before attempting, I think. I can look up pin numbers if you want to try. Think I mentioned them earlier in the thread, but I'll double check. 2005 BBZ, yeah?

Inj 1 pin 2 purple/brown - ECU pin 96

Inj 2 pin 2 purple/green - ECU pin 97

Inj 3 pin 2 purple/yellow - ECU pin 88

Inj 4 pin 2 purple/blue - ECU pin 89

 

All should read zero Ohms from end to end of the wires.  The fact that your problem is intermittent makes me wonder if you'll spot anything though.

[sepulchrave]

How would I test the voltage of each injector plug?

 

This question ^^ tells me you really need an auto electrician.

[Avante]

I figured I'd need a multimeter, but with suggestions relating to wiring up a light bulb and wiggling cables I'd have thought there may be another method. I'll get a friend of mine to let me use his multimeter.

[Avante]

Over a period of time driving, getting used to driving and learning how an engine should work etc - I've noticed a few strange things my car does, attempted to research it myself, and thought to ask for more experienced feedback; When rolling in gear, without applying any acceleration, I can hear a hissing noise, sounds like It's coming from my front/rear passenger side wheel area maybe? The little research I've done into this leads me to believe It's the brake servo or something? I'm not familiar with what one of these are or if It'll affect my misfiring problem, but I've learnt they can be expensive to fix; What's the implications of my not sorting this hissing problem out? It only hisses while I'm rolling, in gear, and not applying any acceleration - As soon as I put my foot on the accelerator, even slightly, it'll stop hissing - It's not a constant hiss either, It's almost every 2-3 seconds, and not every 2-3 seconds either. Almost like it's relieving a build up of pressure from somewhere?

 

I  still haven't gotten to the bottom of my misfiring problem either, but I've found while Idling at traffic lights, if I hold about 2k revs It'll not loose power and the engine management light wont come on - I suppose it's back to the drawing board with this one, I'll find time to check spark plugs over for oil burn marks, I'll check my coil pack for this cylinder, I've already ruled out fuel injector by swapping one over and the problem persists with cylinder one. Am I right in thinking it's more than likely a problem with my spark, or wiring loom?

[Avante]

Also I started my engine with map sensor plugged in lightly, revved slightly and removed sensor, engine seems to stay the same but the EPC light comes on. My worry is the clip for the sensor is broken so I need to find a way to secure it on so it doesn't wobble loose while driving - it hasn't done so far, but just to be safe - any suggestions on my last post? Waited a few days but still haven't got a response. Has all hope been given up on me? Lol

[Breezy_Pete]

Brake servo is driver's side (just behind/under where the brake fluid reservoir is, big black round thing) so doesn't obviously seem to relate to your description of where the hissing is coming from. Without hearing it, I really can't quite imagine what this might be.

 

For the misfire, I continue to recommend a compression test. It should cost relatively little at an independent Skoda/VAG specialist garage, or I would be happy to have a go myself if you ever venture near Oxfordshire. It might well be wiring-related, but you'll spend lots of time/effort/money getting nowhere if there's a 'deeper' reason for the misfire like low compression on that number 1 cylinder.

 

MAP sensor, is either being sucked into it's mounting hole (any time except wide-open throttle), or has approx. equal pressure either side of it (@ wide open throttle) so should tend to stay put really, irrespective of clips being broken. There should never be any positive pressure pushing it out.  Might be worth replacing the o-ring though, if it's a loose fit? You don't want air leaking in past that, as you've discovered.

[Avante]

Thanks Wino, I'll try get a sound recording of the "Tssss'ing", but that's all it is really, a quiet " tsss" noise that lasts for about half a second. It sounds like its coming from the passenger side wheels as I can only hear it with the passenger window open, but I could be mistaken about it coming from the wheels as its hard to tell as it only happens when I'm driving lol.

I'll get in contact with a specialist and get a quote for a compression test as you suggest. Hopefully get to the bottom of the ticking sound when accelerating when in second gear moving slowly, as driving in slow traffic.

And something fell out of the sensor, like a plastic clip, so put it back in and it stayed in. It did slide off slightly without the plastic clip. I don't understand how these sensors work then? I presumed it was just wired to the ECU? I'd never have thought pressure would be involved?

[Breezy_Pete]

The MAP sensor is a pressure sensor (and a temperature sensor) that is wired to the ECU. It measures the pressure in the inlet manifold, and so has to poke through a hole from the outside world, into the inlet manifold.  The pressure in the manifold is always lower than the pressure outside it (though only just when the throttle is wide open) so there's usually a pull sucking it into the hole in the manifold, and never a push trying to pop it out of the hole. Is that any clearer?

[sepulchrave]

There is no clip on the MAP sensor, it's held in place by a torx screw, there is however a clip on the plug which connects the wiring loom to the sensor, if you've snapped the clip on the plug then try using a cable tie to hold it in place.

[Breezy_Pete]

Good thinking ^, that might be what he's referring to. But on BBY anyway, the sensor seems to be held in place by plastic clips, or looks like it on my Polo. Photo shortly.

 

Edit: must admit, when I first looked at this, I thought some lazy sod had replaced it and left the screws out, but that plastic clip seems to be what holds it in:

 

 

Sorry about the funky angle, lots of stuff in the way.

[Avante]

There's definitely no torx screw on mine, just a plug that clips in like the fuel injector connectors do.

I understand better now thanks Wino, my engine was off at the time when it slid off the connector slightly.

[Breezy_Pete]

OK, so you were talking about just removing the connector from the sensor, not the sensor from the manifold?

In which case, the pressure conditions are completely irrelevant.

[Avante]

Makes better sense now, no I've never removed the actual sensor, just the connector bit - how much roughly would we be talking for a compression test from a garage?