The intermittent misfire mystery

[adski]

Hi all,

got a problem with an intermittent misfire and I'm hoping someone with more knowledge and experience than me can shed some light!

The motor...

2005 A3 sportback 8PA 2.0 fsi (non-turbo) engine code BLR

The situation...

Had timing belt, water pump and full service (inc. fuel filter) done a month ago.

Car ran beautifully (as it did before) for a week after, then started missing on cylinder 2 (from obd2 scan). Didn't happen often, was always between 2-3000 rpm but getting above 3000 would clear it. Replaced plug (even though was just done during service) and coil pack on cylinder 2. Didn't solve it and gradually started missing on 4 as well as 2 (again only every now and then).

Took it to local garage (not vag) and they replaced the other 3 coil packs. They reckoned they had sorted it. Drove home, same issue, turned around and went back. They didn't know where to go from there (other than start fault finding with a blank cheque) and I had work comittments to return to so had no option but to do a long journey with the A3 doing as it pleased, sometimes missing like a *****, sometimes smooth driving. Was almost like it was getting stuck in it's misfire zone and then out of nowhere it would clear and be fine again.

Anyway, made it and have avoided using much since, other than to fault find! Been through the vacuum lines, although I sometimes think I can hear a leak I cant find it with water / carb cleaner, so maybe it's the mind playing tricks! Went for a test the other day and she drove brilliantly for 20mins, then got stuck in misfire zone again!

Codes are...

P0300 random/multiple misfire

P0302 misfire cylinder 2

P0304 misfire cylinder 4

Doesn't seem to matter if she's hot or cold, just does it when she wants, and doesn't when she doesn't! Sorry for the essay people, but thought the more info, the more chance one of you could help! I'm up in the mountains so vag com is a long way away!

Thanks in advance all Done a lot of forum searching but not found the key or the secret yet, just hoping for sage advice before I bite the bullet and go a long way in search of vagcom!

 

[ch1z64]

I have similar problem mine is Cylinder 2 and I am wondering if it's the spark plugs , so I am going to change them out see what that does if nothing then new coils and see what happens .
If it's cylinder 2+4 take the coil out of 2 and move to 3 and see if fault moves

 

[adski]

I have similar problem mine is Cylinder 2 and I am wondering if it's the spark plugs , so I am going to change them out see what that does if nothing then new coils and see what happens .
If it's cylinder 2+4 take the coil out of 2 and move to 3 and see if fault moves

Thanks for the reply mate, but tried that and it doesn't move. Hope yours is as simple as the plug, let me know if not!

 

[ch1z64]

Tried my old spark plugs back in and it is still there

 

[adski]

Well, if it doesn't turn out to be ya coil, watch for more suggestions (hopefully) below let me know what happens with yours

 

[Daveyonthemove]

Timing may have slipped a tooth?

 

[adski]

Yeah considered that (seeing that it started a week after the timing kit was done, but ruled it out assuming the problem would be constant if that was the problem. Or you reckon should I not assume this? Cheers for the message

 

[samuelh_888]

Try new plugs, then after moving the coils about and if no change get a new set of coils. If this still doesn't solve it then look at getting your injectors tested.

In the interim get the timing checked

 

[Daveyonthemove]

If the last work carried out on the car was the timing belt, and the car runs poorly since that work then I would look at getting it checked ASAP to rule it out.

 

[adski]

Hi all, thanks big time for the replies!

Sage advice, was thinking I'll have to bite the bullet and check the injectors (not the easiest job on this engine from what I've seen - any advice on this would be sweet!)

Will have a look into the timing too, although I'm still running with the assumption that it would be a constant issue if this were the problem, not a random, intermittent issue?

Big thanks for the advice..

 

[prt57]

When I had a misfire on my Mk 4 Golf I could smell the sulphurous fumes from the cat quite strongly with the car on the drive. The cause was a faulty ignition amplifier for cylinder 3. (No separate coil packs on this car) The smell must have been Unburnt fuel entering the cat.
So by deduction, if you have a strong smell it could be ignition related. No smell could point to the fuel system with the injector being partly blocked or weak pressure from the pump.
As mentioned, I would have the cambelt timing checked.

 

[ScottyP45]

Ideally you need some diagnostic kit, just order vcds from eBay or your hunting in the dark. That way you can log some stuff and see what jumps out, once you've bought it the rest is free testing. Doesn't have to be the expensive version of vcds...

Anyway here's some things to think about or check: (since you're stuck)

Crank sensor.
Cam sensor.
Fuel pressure sensor.
Cam pulley slack? (If your engine has adjustable pulley, could be wandering)
Weeping head gasket (compression test & check coolant level)
Leaking fuel rail (may just evaporate so fuel pressure logging would confirm)

They could have knocked or loosened something when they worked on it. Is the fuel filter sealed tight?

Since you seemed to rule out plugs and coil packs on cyl 2 and 4, these may just be random and not actually related to those cyls if it's a common item, or could be fuel pressure to those cylinders sometimes drops out, or water seeps in from a weeping gasket. Just some humble pointers, and could still be injectors as previously said.

Fuel, spark, compression and timing are all potential culprits

 

[ron burgandy]

Mine has the same fault on cylinder 2 I’ve replaced ignition coil and spark plugs to no effect

 

[Retroman]

I would also be suspicious of something not quite right after the maintenance/service. Coils often only show a problem as non-specific misfires but are often worse on a hot engine. The fact that this seems to be restricted to certain rev ranges does tend to point to ignition timing and I personally, would want to be sure that the timing is "spot on" after the cam belt change. I do not know where your particular camshaft(s) sensor(s) are for your particular car but often they are disturbed when a cambelt change is done and I've known wiring to get pinched/damaged and connections not properly connected.

I agree with also checking/eliminating the fuel filter from the problem. Is it sealed properly and is it facing the correct petrol flow - both easy human error mistakes even for professionals?

 

[K96]

Hello,

I am also suffering from an intermittent misfire on cylinder 4 I've changed all 4 coil packs twice and spark plugs twice just to make sure they weren't the problem.

I ran some diagnostics and got the following values. If somebody could have a look and see if all these values are normal. If any of the values are abnormal let me know.

Car is a S3 8P S-Tronic. Stage 1 Map. No other mods.

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[K96]

Anyone able to help with the above ?

I took it to a "specialist" today they suspect a faulty injector is at fault so will get it replaced next... hope it does the trick...starting to fancy a change after all this

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[doce]

Please update the topic if you fix this. My friend has the same problem for a long time but he can not find out what the problem is. Same error codes but CAXC engine. He has already replaced spark plugs, ignition coils, cleaned injectors with wynn's machine, also cleaned throttle boddy, inlet manifold etc but without success.

 

[samuelh_888]

Hello,

I am also suffering from an intermittent misfire on cylinder 4 I've changed all 4 coil packs twice and spark plugs twice just to make sure they weren't the problem.

I ran some diagnostics and got the following values. If somebody could have a look and see if all these values are normal. If any of the values are abnormal let me know.

Car is a S3 8P S-Tronic. Stage 1 Map. No other mods.

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VCDS is diagnostic software that’s near VAG dealer equivalent. Putting your code in to the Ross-Tech site (who make VCDS) gives this:

http://wiki.ross-tech.com/wiki/index.php/16688/P0304/000772

Your ‘specialist’ should be able to diagnose though.

 

[K96]

VCDS is diagnostic software that’s near VAG dealer equivalent. Putting your code in to the Ross-Tech site (who make VCDS) gives this:

http://wiki.ross-tech.com/wiki/index.php/16688/P0304/000772

Your ‘specialist’ should be able to diagnose though.

Hello,

I've changed quite a few of the parts on that list already so next up is the injectors. Sam if it matters I only started to get misfires after I changed the N80 purge valve do you think they could be related in some way or just purely coincidence?

Specialist wanted to charge me £660 to change 1 Injector so taking it to my usual garage who will do it at a fraction of the cost. Should of just went there in the first place

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[ron burgandy]

I found my problems started when I went from v powe to normal petrol on a cost cutting exercise

 

[samuelh_888]

A bad N80 can cause the engine to run terribly and possibly misfire. Was it a new/genuine item you fitted? Check that the hoses are on correct and the electrical plug connected properly.

I replaced mine and I had a strong fuel smell and it’s been fine since.

Where are you based? Before you get new injectors get your current ones ultrasonic cleaned - RTech do them and I think they’ll do mail order too. If the spray patterns are down and can’t be salvaged they’ll let you know. Three of mine were perfect, £80 for a new replacement of the 4th injector.

 

[K96]

A bad N80 can cause the engine to run terribly and possibly misfire. Was it a new/genuine item you fitted? Check that the hoses are on correct and the electrical plug connected properly.

I replaced mine and I had a strong fuel smell and it’s been fine since.

Where are you based? Before you get new injectors get your current ones ultrasonic cleaned - RTech do them and I think they’ll do mail order too. If the spray patterns are down and can’t be salvaged they’ll let you know. Three of mine were perfect, £80 for a new replacement of the 4th injector.

It was a new item I fitted. Got a Bosch one...but I'll ask my mechanic to double check all the hoses are on correctly. Now you've said that it does make sense. I'll get this checked today hopefully.

I'm based in Birmingham I have already ordered a new injector but it will take 3-4 days to arrive so hopefully have it fitted by the end of the week. What other symptoms did you have when your injector was faulty?

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[Gaz78]

As a thought MidlandsVW aren't too far away from Birmingham , and they come highly recommended by ones on here . Might be worth a visit to them??

Gaz

 

[samuelh_888]

It was a new item I fitted. Got a Bosch one...but I'll ask my mechanic to double check all the hoses are on correctly. Now you've said that it does make sense. I'll get this checked today hopefully.

I'm based in Birmingham I have already ordered a new injector but it will take 3-4 days to arrive so hopefully have it fitted by the end of the week. What other symptoms did you have when your injector was faulty?

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I didn't notice any issue with the injectors. When I went for the remap and had the injectors removed for the ultrasonic clean, one of them failed the spray and leakdown test. Sometimes they can recover the injector but not this time.

R-Tech in Nuneaton aren't too far away.

 

[K96]

Just to update everybody had the engine stripped down today and inspected properly this time. My high pressure fuel pump isn't working properly which makes sense because my car is fine up until about 4/5k revs then after that it starts struggling.

Now need to get hold of a high pressure fuel pump and hope that's the fix...

I can see why most of us are still having misfire issues as I've never seen anyone say they've changed the fuel pump but we've changed the usual suspects sparks, coils fuel injectors etc

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[samuelh_888]

I can see why most of us are still having misfire issues as I've never seen anyone say they've changed the fuel pump but we've changed the usual suspects sparks, coils fuel injectors etc

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The hpfp has a very low failure rate, I’ve never seen or heard of one fail. And they aren’t cheap so not the first port of call to replace!

Are you certain it’s the fuel pump and not the fuel pressure sensor? Maybe a faulty fuel pressure relief valve cracking too soon?

 

[ch1z64]

Small update on my situation , mechanic looked at it and done relevant tests and nothing to indicate it was mechanical so because off this he mention it would be more chance it being electrical due to the fault not moving and noticing ( I did too ) that the connector #2 wasn't fully clipping into the top off the Coil pack as the clip inside coil connector had broke so that could be causing the intermediate misfire too .
So he recommended to try and get something to pull the loom into the coil pack connectors so I used some tie wraps around each part off loom and coil head and will report back later once I do another Autoscan

 

[ch1z64]

My last update on this subject until it's definitely fixed , did what mechanic suggested and still getting misfire on #2 plus the intermediate fault ( still think it's electrical tho ) but now I will get in contact with the Audi guy and pay through the noise to get to the bottom off this problem as it's doing my head in

 

[K96]

My last update on this subject until it's definitely fixed , did what mechanic suggested and still getting misfire on #2 plus the intermediate fault ( still think it's electrical tho ) but now I will get in contact with the Audi guy and pay through the noise to get to the bottom off this problem as it's doing my head in

I'm having the exactly same issue. Ive been told I have a cracked cylinder head possibly but surely I would know about this if I've been driving with a cracked cylinder head for months???

I'm also leaning towards electrical now everybody is at a loss. Close to just breaking my car and getting something else as I've had enough spending money on fault finding

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[ch1z64]

Now my misfiring problem has been resolved and it did look like electrical but after replacing spark plugs with a great Quality and then upgrading to R8 Red Coils it seems my fault has gone away and car seems to pull like it should do . Now not saying for one minute this will be a solution to everyone's but it worked for me .
Electrical problem was thought as problem never moved when cool was moved

 

[ch1z64]

Well I thought I had fixed this F**ker but alas not as I have got faults again but it has changed to intermediate now , where do I begin now

 

[doce]

Carbon build up on the intake valves?

 

[ch1z64]

Carbon build up on the intake valves?

Had a walnut clean done around 18 MTHS ago so would be hoping for no carbon build up that quickly , plus I only put shell Vpower in her

 

[K96]

Well after a long and frustrating couple of weeks with my car my problem has now been solved. Changed the fuel injector on cylinder 4 and the car is back to normal !!!! I'm so excited I could cry

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[samuelh_888]

Try new plugs, then after moving the coils about and if no change get a new set of coils. If this still doesn't solve it then look at getting your injectors tested.

In the interim get the timing checked

Yep!

 

[Gaz78]

Well after a long and frustrating couple of weeks with my car my problem has now been solved. Changed the fuel injector on cylinder 4 and the car is back to normal !!!! I'm so excited I could cry

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RESULT

Gaz