AUA 1.4 misfire cylinder 2 - trim readings

[tuizner]

no - just the 4 green seals.

all back together again and problem remains. At least I (think I) know that in the main the engine looks good.

During readiness testing VCDS at revs you can hear what seems to be the purge valve amost competing with the engine sound - it may be somthing else of course as it seemed to follow the rpm for Hz.

Idle revs seem low at 670 or so (and will misfire at this). Even a tiny bit of throttle to 800 stops the misfire though...

Garage thought it could be timing but surely that would show always and not just throw a mosfire at hot idle?

A friendly passing dog walker / mechanic thought it may be tappet / valve clearance showing up at hot.

 

[birtyA2]

no - just the 4 green seals.

all back together again and problem remains. At least I (think I) know that in the main the engine looks good.

During readiness testing VCDS at revs you can hear what seems to be the purge valve amost competing with the engine sound - it may be somthing else of course as it seemed to follow the rpm for Hz.

Idle revs seem low at 670 or so (and will misfire at this). Even a tiny bit of throttle to 800 stops the misfire though...

Garage thought it could be timing but surely that would show always and not just throw a mosfire at hot idle?

A friendly passing dog walker / mechanic thought it may be tappet / valve clearance showing up at hot.

Determined stuff this. Did you manage to retrieve ‘the red thing’ in your photo?. On to idle, my AUA drops to something around 700rpm when up to temperature from memory, I’ll have to check to confirm. When cold at first start idle is around 1000rpm, again from memory. Just to confirm, are you saying that once hot, if you apply just the smallest amount of throttle to bring the revs to around 800rpm the misfire disappears? Are you able to capture that on VCDS?. What would be the indicated temperature and indeed the temperature indicated via VCDS be at this point in time. And finally (sorry about the endless questions) is this repeatable, that is, is it always the case that with the engine up to temperature you can ‘break through’ the misfire by raising the revs to around 800rpm, only for the misfire to return when you release the throttle and let the revs drop to the hot idle of around 670rpm

I’d be surprised if tappets were causing this. On the AUA they have a reputation of being a bit clattery, but I remember from earlier in the thread you mentioned an oil change and tappet cleaner having been done

J

 

[tuizner]

during this test below - fuel gauge started going haywire - needle moving up and down,,,,

digging further in vcds

no resistance bank 1 sensor 1 on block 41

idel speed set quite low at 678 block 50

no voltage supply block 61 EPC

 

[tuizner]

Determined stuff this. Did you manage to retrieve ‘the red thing’ in your photo?. On to idle, my AUA drops to something around 700rpm when up to temperature from memory, I’ll have to check to confirm. When cold at first start idle is around 1000rpm, again from memory. Just to confirm, are you saying that once hot, if you apply just the smallest amount of throttle to bring the revs to around 800rpm the misfire disappears? Are you able to capture that on VCDS?. What would be the indicated temperature and indeed the temperature indicated via VCDS be at this point in time. And finally (sorry about the endless questions) is this repeatable, that is, is it always the case that with the engine up to temperature you can ‘break through’ the misfire by raising the revs to around 800rpm, only for the misfire to return when you release the throttle and let the revs drop to the hot idle of around 670rpm

I’d be surprised if tappets were causing this. On the AUA they have a reputation of being a bit clattery, but I remember from earlier in the thread you mentioned an oil change and tappet cleaner having been done

J

Hi J

No problems with the questions

I did manage to vacuum the red thing out but my muslin trap on the vacuum didnt work so it got sucked into the vacuum..,

min also starts at 1000rpm and drops on warm but is set at 678rpm (VCDS).

i cannot guarantee that every time addiing a slight throttle stope the misfire but it is certain that the misfire only occurs at idle so it makes sense. I only tried adding a slight throttle today which seemed to work - I will try again next week to see.

I changed thermostat and sender today (just in case) to no avail but I think the misfire is occuring when the needle moves on teh gauge but I think I have seen it happen at lower temps on VCDS also,,,

Yes - it is very very repeatable. when warm and throttle is added the engine runs sweet - misfire only appears on idle. You can drive for miles without issue only to stop at a junction and misfire - I have an ODBII plugged in to reset the misfire - then is OK for a 10 seconds before misfire returns on the counter (will be constantly misfiring but EML only comes on when misfires = 400 or so). If you raise the rpm with a slight throttle then no misfire. let idle = misfire.

yes Wynns tappet / valve additive added to oil but not sure how long it takes to work...

 

[birtyA2]

Ah this is interesting, what temperature was the engine when you took the block 50 measurement? I ran this on mine from cold and the target was initially around 1000 rpm and the actual around the same. As the engine warmed the target slowly decreased with the actual more or less tracking it down. So assuming yours was from cold as well the target was set absolutely too low I would say. That said it doesn’t misfire until it warms up. What is the difference between target and actual idle once it’s up to temp?

 

[tuizner]

All those vcds blocks from the same time so 91C temp. The actual is me with a little throttle to stop misfire. I would say that the target and actual are the same if I let go of the throttle.

The text file for block 50 says target spec though should be 800

 

[mtl]

Mine is also set to 678 when warmed up to operating temperature.
Turn on A/C and the idle will be higher. Does it misfire also with A/C on?

 

[tuizner]

Mine is also set to 678 when warmed up to operating temperature.
Turn on A/C and the idle will be higher. Does it misfire also with A/C on?

yes rpm goes up to about 800 with AC but still misfires

Wondering if it is the throttle fly by wire. There is no voltage on block 61 at idle showing. Am going to see if that changes on throttle. Would someone look at their block 61 please? It might be that no voltage is the norm...

 

[birtyA2]

yes rpm goes up to about 800 with AC but still misfires

Wondering if it is the throttle fly by wire. There is no voltage on block 61 at idle showing. Am going to see if that changes on throttle. Would someone look at their block 61 please? It might be that no voltage is the norm...

So this is block 61 on mine not quite up to temp. No value for Supply Voltage either, broadly the same as yours. Apologies, I only have an unregistered copy of VCDS Lite at the moment, so taken from VAG401. I’m not sure this will be throttle body related as I would expect you to see misfire across all cylinder. From the other scans your misfire seems to be mostly showing on cylinder 2 by some margin, so logically it should be something linked to that cylinder, so injector/spark plug lead/injector lead or plug etc

 

[PlasticMac]

I'd like to know what happens if you block the "port" on the ACF.
I'm convinced all is not as it should be there, and air being taken in via the Evap will affect mixture.
Mac.

 

[tuizner]

So this is block 61 on mine not quite up to temp. No value for Supply Voltage either, broadly the same as yours. Apologies, I only have an unregistered copy of VCDS Lite at the moment, so taken from VAG401. I’m not sure this will be throttle body related as I would expect you to see misfire across all cylinder. From the other scans your misfire seems to be mostly showing on cylinder 2 by some margin, so logically it should be something linked to that cylinder, so injector/spark plug lead/injector lead or plug etc

View attachment 111160

Thanks appreciate it.

I agree but seems most folk with a misfire on aua engines happens on 2 so maybe it's the weak cylinder and goes first?

Have changed all of the key ignition elements with quality NGK parts apart from post cat lambda.

The other missing value I had was block 041 with no resistance on bank 1 lambda. Any chance of a check on that pretty please . could be a dodgy wire from lambda to ECU...

 

[tuizner]

I'd like to know what happens if you block the "port" on the ACF.
I'm convinced all is not as it should be there, and air being taken in via the Evap will affect mixture.
Mac.

Have an eBay unit ordered to check this off. £16 will be well spent if it is.
Only thing I can think is may be there should be a one-way flap in that port that allows build up of pressure to vent under non-running applications, but when the vacuum is applied it closes..

Will get gaffa tape out and check

 

[PlasticMac]

Have an eBay unit ordered to check this off. £16 will be well spent if it is.
Only thing I can think is may be there should be a one-way flap in that port that allows build up of pressure to vent under non-running applications, but when the vacuum is applied it closes..

Will get gaffa tape out and check

If the "port" is a valve of some kind, (safety, or non return), but is now stuck open, then maybe the line to line to the tank is blocked, so the vacuum has nowhere to draw from.
Yes, gaffer tape is a good check.
The AUA, cylinder 2 thing is a mystery which would be nice to solve.
Mac.

 

[birtyA2]

Thanks appreciate it.

I agree but seems most folk with a misfire on aua engines happens on 2 so maybe it's the weak cylinder and goes first?

Have changed all of the key ignition elements with quality NGK parts apart from post cat lambda.

The other missing value I had was block 041 with no resistance on bank 1 lambda. Any chance of a check on that pretty please . could be a dodgy wire from lambda to ECU...

I think you may be right, cylinder 2 has come up in thread’s a lot though why that is I have no idea.

On to block 41, you may be onto something here. So first picture is ignition on, engine not started



This second picture is block 41 after the engine had been running for about 1 minute. The engine won’t have been fully cold as had been run earlier but will not have been fully up to temperature

 

[tuizner]

If the "port" is a valve of some kind, (safety, or non return), but is now stuck open, then maybe the line to line to the tank is blocked, so the vacuum has nowhere to draw from.
Yes, gaffer tape is a good check.
The AUA, cylinder 2 thing is a mystery which would be nice to solve.
Mac.

have blown down the line from the purge valve and you can hear the fuel tank pressurising so seems OK

 

[tuizner]

I think you may be right, cylinder 2 has come up in thread’s a lot though why that is I have no idea.

On to block 41, you may be onto something here. So first picture is ignition on, engine not started

View attachment 111174

This second picture is block 41 after the engine had been running for about 1 minute. The engine won’t have been fully cold as had been run earlier but will not have been fully up to temperature

View attachment 111173

many thanks - will check that block again now.

 

[tuizner]

many thanks - will check that block again now.

engine off = no value

engine on - still nothing

will need to trace that wiring now but hopefully this is the problem

 

[birtyA2]

engine off = no value

View attachment 111175

engine on - still nothing

View attachment 111176

will need to trace that wiring now but hopefully this is the problem

Ah yes OK, this does look promising. I assume that Sensor 1 is the lambda probe just before the 1st cat that is part of the exhaust header/manifold (not sure what the correct term is). There is a chance that this was supplied as faulty or indeed that there is a continuity problem with the wiring or indeed the connector is not fully seated. I had a self inflicted problem with my EGR not adapting recently after removing to clean, it was only when I squirted some switch cleaner in the connector and reseated a few times to clean the contacts that all was OK, worth a try.

 

[tuizner]

I took the new NGK lambda off yesterday so have it here - tested it according to workshop manual.

First off the pin numbers do not line up. Assuming the harness nubers are correct (bottom image) then I do get a correct reading between 1+2 but no resistance readings for any other combination of the other 4 pins on the lambda side. manual suggest should get 2.5-10 ohms on 3+4.....

 

[tuizner]

hmm - same results on the "old" sensor -

so either
both are faulty
the wiring diagram is wrong
or I have used the wrong diagram but I think the AUA has the mm-mpi system?

Audi Workshop Service and Repair Manuals > A2 > Power unit | MM-MPI injection and ignition system (4-cylinder) | Mixture preparation system, electronic inj.,Gas | Checking components | Checking lambda probe heating for lambda probe before catalytic c

A2 > Audi Workshop Service and Repair Manuals > Power unit | MM-MPI injection and ignition system (4-cylinder) | Mixture preparation system, electronic inj.,Gas | Checking components | Checking lambda probe heating for lambda probe before catalytic converter

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