1.4 Petrol Misfire (P0303) - Help to diagnose?

Mophim

Member
Hello

I've had to do a few things to a newly purchase 2000 (X Reg) A2 petrol 1.4.
It has a coil pack & spark plugs.

It's started misfiring on cylinder 3 (error P0303) as well as an intermittent P0302 (cylinder 2). This is something that has just started to happen after I've fixed other things. I've read the generic 'possible causes' for this code but think it's electrical.

Prior to this, it failed it's MOT last week due to the airbag light being on as well as an emissions failure. It had the EML (engine management light) as well as the ESP light illuminated.

I have an old, generic usb / communication lead as well as the 'VWTool' software.

With the lead & software is was able to clear the airbag light fault (which hasn't reappeared) as well as fix the other faults. The EML problem was the blowing of fuse 31 which is linked to the ERG valve. The actual problem was the oil breather heater? which I have temporarily disconnected. The fuse no longer blows.

I also removed the ERG throttle body & cleaned it then reset it via the VWTool.

This cleared all of the codes and all looked OK. However, it developed the P0303 error code & runs as rough as a bag of spanners.
I can't get the emissions retested with it running like this.

Plug 3 has no spark. I'd already changed the plugs when we got the car but the old ones looked quite new. It was running OK before & after the change. I've used one of the old plugs to check everything. The no 3 lead works as I swapped it with another so I don't think it's the plug or lead.

So, here (finally) is are my questions:

1. How would I go about checking the coil pack (looks like a flat distributor)?
2. Is there something I could have messed up, doing any of the above that might cause this? Either physically, like disconnecting the breather heater or removing the throttle body or maybe a setting via the software?
3. Can I check the coil voltages? If so, what do I need to do?
3. Could it just be coincidence that this has failed whilst doing the other stuff? (this is slightly rhetorical)
4. Any other ideas? Anything else I can check? Connections, fuses, blocks via the software? I've monitored the misfires in block 15 of the software & no. 2 seems almost as bad as no 3 although 2 does have a regular spark if I check it.

I'm quite a novice with fuel injection systems with electronic ignition and need to know that if I do need to buy something, it's the right something.
I have until this thursday for my re-test or it has to all be redone : (

Thanks very much if you can point me in the right direction
 
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HI,

The coil pack is a prime source for errors like this, also the injector wiring harness.

Is there any way that you can swap a coil pack without buying one (just in case it doesn't mak any difference?)

But do check the injector wiring too while you are doing that.

I am not sure if the things you have done would contribute to this, but the coil pack is a known weak point.

Steve B
 
Thanks for the reply. No 3 plug spark is non existent. Is there a way to check the output of the coil pack via the ECU?
I don't have access to another without buying one. GSF & EuroCar Parts are maybe £10+ more than ebay.

What's interesting is that when I immediately start the car, it seems to run well for maybe 1 second then revs drop to idle and it's lumpy.
Is there anything via the software settings that could be affecting this?

Also, would a problem with the injector wiring cut the spark?
 
Hi again. I'm really confused

So, after lots of intermittent changes to misfires (via error codes), seems pretty constant on cylinder 2 now, after this being fine!! (the initial problem was almost exactly the same but only no.3)

This is after changing plugs, leads & coil pack.
When monitoring the misfires, 1,3 & 4 are on zero constantly whereas no. 2 is showing maybe 50+ misfires. There is a weak spark at no.2.

I don't understand why just cylider 2 would have such an obvious misfire when the others are all fine.
However, I read this on another thread here from user 'SeSe'
So, main problem is probably with ECU ignition coil driver. There is no freely available datasheet, but possible cause is microchip L9119D – which (probably) control STI bus, k-line, ignition control.

Is this likely? Is there anything else I can check? If it is the chip on the ECU, can it be fixed?
 
I've just found this, also by user Sese but on a different forum ( https://www.picoauto.com/support/topic10493.html ):

Hi! Contact me via pm.
As far as I know, it is not a engine mechanical problem.
ECU is not a cause of problem.
But signal, which go from ECU to ignition coil to 1-2 cylinders is a problem.
But, actual cause is still unknown.

The question is, how ignition signal is formed and which signals do alter ignition signal waveform.
And, why it is only on second and little on 1 cylinder? Misfires are like 90% on second cylinder, and 10% on first.
It have been approved, that they happens because of altered waveform from ECU on ignition coil 1, which drives 1 and 2 cylinders.
But original problem is not in ECU itself. That had been also approved.
It is possible, that on forming ignition signal affects signals from knock sensor, from camshaft position sensor and crankshaft position sensor.

On similar case, it was knock sensor and or wiring to it. How? Nobody is sure.
 
Ok. I appreciate I'm talking to myself here but might as well document my findings in this thread all the same.

This is with regard to monitoring the misfire on cylinder 2 with VWTool software via block 15 of the engine module (block 15 shows cylinders 1-3. Block 16 is cylinder 4) - 1,3 & 4 all show zero misfires. As I said, this is odd because prior to changing the coil pack, it was exactly the same but cylinder 3.

So, block 15 shows cyl 2 misfires around 50 (not sure what the cycle is? Revs / seconds?) when cold then increases steadily until the cam sensor? detects the repetition of the misfire and registers the fault & the ELM (engine management light) comes on the dash. At this point the misfire reaches maximum of the cycle. Maybe the fault shuts off the injector?

With regard to my last post above, I could feel the knock sensor from above. It feels like something is moving about quite close to the actual sensor but am not sure if it's the connector. It's dark now so can't really get underneath tonight.
I also removed the N/S headlamp to look at the earth strap, as a poor earth could also cause issues although I'm not sure it would only affect one cylinder but couldn't find it? Is it there on all cars?

If anyone has any ideas about this,I'd be grateful. The car failed on it's emissions last week & tomorrow is the last day for a retest. I'm fed up with all of this faffing.
 
Do a cylinder compression test..................I had misfires and found out that the cylinder head contained 4 leaking exhaust valves and 4 bit less leaking exhaust valves.
Ended up with 8 new exhaust valves and 8 new exhaust valve guidings................. (car had run 60k miles)
 
Thanks Spike. That's really interesting.
It's funny how an initial fault code leads me on a merry dance from one unexpected thing to another (like engine earthing and a knock sensor).
It's also interesting how this no. 2 cylinder problem seems to haunt quite a few A2 owners.
I'll look at it this morning and see how the connections on the knock sensor look first.

Thanks also, Rolf for your input.
 
Well the car passed the MOT. Emissions were fine. Not sure if this was a result totally of the misfire as this wasn't so pronounced at the first MOT. I think the EGR problem was more likely.

Anyway, I cleaned up the engine earth terminal and checked the knock sensor (removed / replaced the connector and re-torqued the bolt)
This seemed to stop the EML coming on and has improved the misfire but it is still there, just more intermittent.
Think I'll get a new knock sensor anyway and give it a go.

I'll report back at some point to update if this cured it.
 
Hello. It's been a while but I'm going nuts with this cyl 2 misfire. This car is for my son who is learning to drive but he's only been out in it once since September due to this problem & I feel really bad about not being able to get to the bottom of it.
I changed the knock sensor but (typically for me!!) it didn't help. I've also disconnected it as well as reconnect the old one, hanging loosely - all to no avail. It's had new coil pack / plugs / leads, cleaned up earth contacts.

What I will mention is that it's only got 80k (5k a year) and since we've had it (july) we've never taken it on a good, long run. Could this effect anything if, during it's previous life, it's only be run around town? The old oil looked ok (not foamy brown)

This is what happens (physically & misfires monitored via PC):

When cold, the car starts well - no misfires and ticks over about 1100 rmp.
It runs like this for maybe 5 mins, with the tick-over revs slowly dropping.
After this time, the revs reach about 800 - 850 (which seems a little low)
You can feel, through the car, when the misfire begins. It's pretty sudden & doesn't really build up - ie. It doesn't start at one of two per monitoring cycle (15 sec I think) but is pretty much 90 - 100 per 15 secs. The computer confirms this. It's at this point that the 3 min ECU monitoring (or thereabouts) occurs which results in the EML coming on & cyl 2 being cut off.
If I turn OFF the climate control the revs drop further. I don't understand this either.

One further thing. The engine breather pipe has an inline heather in it (when at the front of the car it's down the back left of the engine.) This had a fault when I bought the car which was blowing the ERG fuse, so I disconnected it. Might this cause a single cylinder misfire?

Is there anything else obvious that I may have overlooked? Anything else common to check?

Any help gratefully received. Thanks : )
 
youl find the 1.4 petrols do tick over very low, 800 - 850 seems about right to me as been a while since ive drove my 1.4, if you turn climate on the ecu ups the tick over revs to 900rpm, this is normal and imagined its because of the extra load put on the engine from the AC compressor... Ive had the mis fire headaches last year with mine and tried everything to no avail, earths , wiring, egr, 02 sensors, but always came back, i think it turned out to be an injector sticking in the end as swapped the complete injector rail for another one and cured my missfire, my understanding was the injectors have 2 levels of fuel spray amount, one for say on choke when engines cold , then lower when warmed up, my injector seemed to be sticking fully open as if on choke and then blowing the spark out as such from being over fuelled, the 1.4 aua engines warm up within a couple of miles as there all alloy construction, after this it would start miss firing , hesitating very slightly and sometimes light the dash up like a christmas tree if i did not back off the throttle.. you could try some red X or injector cleaner and maybe a good run may help, more so if its not really been drove since september but its a bit hit n miss finding the fault as could be one of many things causing the fault...
 
I can confirm that when my engine is warm (2000 AUA), tickover drops to about 600 without air conditioner / 800 with AC.
 
Could it be an inlet manifold gasket air leak? Depending on access, you may be able to use carburettor cleaner sprayed around the gasket area with the engine idling. Do mind out though, as it's flammable. If the cleaner gets sucked into the leak, you should notice the engine note change briefly. Then you know the location. All the best, Matt


Sent from my iPhone using Tapatalk
 
Hi guys.

Thanks very much for all of this.
Jigsaw - that's interesting about the primary & secondary injection system as something does seem to change suddenly when warming up, like a relay or some system cutting in.

Thanks for the reassurances about the tick-over. At least I know that's OK.

Based of all of your feedback I'm going to do the following (cheapest first : ) :

Add some decent injector cleaner to the fuel & take it for a good run - at least an hour at full temp.

If not, then spray 'something' around the intake to see if the revs improve.

If that doesn't help, I think initially I'll swap no. 2 injector with one of the others. This will also allow me to properly check all of the intake too.

If i get this far, how does the wiring remove from each injector? They are black plugs with a little metal clip each side. Do they just pull off? Which bit do I pull? Do the clips need to be pulled aside?

Thanks again in advance and again for your responses.
 
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Well, it's been a while. I thought I'd give a final update on this.

I finally advertised this car at the beginning of the year with it's misfire. Long story short - ebay sale - non paying bidder - much hassle - loss of motivation to try selling again.

Fast forward to May 2017. The car has sat at my mother-in-laws house since then (out of sight out of mind ... the car, not the mother-in-law ; )
She's getting understandably fed up it's still there so I'm having a big push to sell again.

The long and the short of this is (as brief as i can make it)
A friend mentioned placing a troublesome PC graphics card in the oven & baking it to gently resolve dry joints (something like that anyway)
So, I figured I had little to lose with an experiment with my ECU. I didn't want to oven bake it (too risky) so I took the lid off (much sticky sealant) then placed it on my utility room radiator overnight - this rad stays on and is pretty hot.
Next day, put it back together (case was almost too hot to touch) put it back in the car and guess what?? ... no misfire.
I let it idle for maybe an hour whilst I cleaned the car (it was parked under a willow tree - much sap) and the EML didn't come on and the tickover was stable. I also drove it around the block and it seemed much more responsive. Previously, it would make about 3 mins idling before the EML came on & the ECU shut down no. 2 injector.
I'm happy about this but fed up that I didn't try this much earlier, when my son was learning to drive.

Anyway, I'm still looking to sell it so please check out the 'for sale' section. Cheers, Gary
 
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