FSI - Partial Fuel Trim too high?

stew said:
Thanks guys.

Coil packs are Bosch and less than 2 years old. Swapped around previously and code stayed on the same cylinder.

I did have the actuator for the flaps replace in 2018 due to a broken rod. At the time the flaps were quite clean and working correctly, but that was about 40k miles ago. I'll take a look a measuring block 142 when I next get time to pick this up again.

Should the flap be closed at lower rpm? I think this could be worth a look.

Another possible curveball, and something I forgot. A year or so ago I noticed that the EGR pipe had a leak. At the time I blanked this using a blanking plate for a Renault that allowed for movement of the EGR valve. I'm wondering whether I've got an air leak here, my thinking being EGR could be closed at idle but then opens under load allowing unmetered air in. Will also look more closely at that maybe see what there is in VAGCOM to get data for the EGR operation.
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The "closed loop" nature of the FSI's engine software may not be compatible with EGR mods.
Mac.
 
I've got a maf sensor I could send out to you to try if you wanted? I had the same horrible problem with previous FSi, and it turned out to be the injector that had decided to throw a hissy, replaced all four injectors and the fault cleared once and for all. A failing HPFP can also throw this kind of random misfire, but for me it was basically throw parts at it until it cleared...the final throw of the dice was new injectors...and hey presto all sorted, but these cars like to be an enigma of confusion for us owners!!!!
 
Clackers said:
I've got a maf sensor I could send out to you to try if you wanted? I had the same horrible problem with previous FSi, and it turned out to be the injector that had decided to throw a hissy, replaced all four injectors and the fault cleared once and for all. A failing HPFP can also throw this kind of random misfire, but for me it was basically throw parts at it until it cleared...the final throw of the dice was new injectors...and hey presto all sorted, but these cars like to be an enigma of confusion for us owners!!!!
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Thank you, that's a really kind offer. I guess that's any easy way to either confirm or rule it out. I'll message you.
 
Good Evening Stew,

I hope these are of use to you.

You did not specify engine state requirements so I went with engine running and warm, at idle.

1690919556793.png



1690919715471.png


And one with engine working a bit harder.

1690919917096.png


Happy to do more.

Andy
 
PlasticMac said:
The flaps are held in the up, (active), position in stratified and homogenous lean mode, by engine vacuum via the actuator.
The flaps drop down, by return spring when vacuum is removed from the actuator, (controlled by a solenoid valve in the vac line).
In general, the flaps are no longer active above about 2,850rpm.
The flaps are binary, up or down, not variable.
It would be interesting to know if the engine runs without miss fires above 3,000 rpm.
Mac.
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I've had another look at the misfire log I put up yesterday. Its not conclusive, but it does appear to be misfiring at higher RPM (3000-4500), however the count in relation to the RPM is lower than at idle.

My immediate thought is air leak.
 
Andrew said:
Good Evening Stew,

I hope these are of use to you.

You did not specify engine state requirements so I went with engine running and warm, at idle.

View attachment 111345


View attachment 111347

And one with engine working a bit harder.

View attachment 111348

Happy to do more.

Andy
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Thanks Andy. The obvious is my sensor 1 partial load (MVB032, second reading) is way too high at 16.4%. I think this is where I need to start. Your lambda aging figure (MVB034, third reading) is also much better than mine. From what I've read my number looks ok but I'm going to check again and also compare voltage with yours.
 
stew said:
Thanks Andy. The obvious is my sensor 1 partial load (MVB032, second reading) is way too high at 16.4%. I think this is where I need to start. Your lambda aging figure (MVB034, third reading) is also much better than mine. From what I've read my number looks ok but I'm going to check again and also compare voltage with yours.
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God Afternoon Stew,

You have lamented previously that there no BAD specification available which is largely true and a reason I keep posting VCDS Groups for my FSI for this that and the other, however there is some information built into VCDS.

Quite often if you move the cursor over a measuring block displayed value you get a pop-up window which gives the value range for whatever you are looking at but the trouble is I often forget this is available. This information is also listed in the label file which maybe useful if you do not have VCDS plugged into the car.

Specifically MVB032/2 and the 16.4% value that concerns you, hover the cursor, and you will see Value Range -25%.....25% so well within range but a little high compared with mine but I have little knowledge of the subject Fuel Trims and cannot comment further.

Andy
 
Andrew said:
God Afternoon Stew,

You have lamented previously that there no BAD specification available which is largely true and a reason I keep posting VCDS Groups for my FSI for this that and the other, however there is some information built into VCDS.

Quite often if you move the cursor over a measuring block displayed value you get a pop-up window which gives the value range for whatever you are looking at but the trouble is I often forget this is available. This information is also listed in the label file which maybe useful if you do not have VCDS plugged into the car.

Specifically MVB032/2 and the 16.4% value that concerns you, hover the cursor, and you will see Value Range -25%.....25% so well within range but a little high compared with mine but I have little knowledge of the subject Fuel Trims and cannot comment further.

Andy
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This may help too, Group and Block descriptions. Supports the new BAD lable file.
Mac.
 

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Well, no difference with an alternative MAF. My other half says I have better things to do with my time, so I've reduced the price in the advert. If it doesn't sell it will make a different driveway ornament.
 
May I chip in with a question?

My A2 had a misfire on Cylinders 2 and 4 after changing the spark plugs and Coil packs it seemed to have cured the misfire for about a week and now it's back. The car suffers from a lack of power in the lower revs until it reaches 3000rpm where the car seems to pick up and accelerate through the gears. I have noticed that in 5th gear and at a low speed, I think I can feel the car miss so I then drop into 4th, which cures the issue.

Do you think i have an issue with the actuator not working as it should?

regards
Jae
 
Stan2stan2 said:
May I chip in with a question?

My A2 had a misfire on Cylinders 2 and 4 after changing the spark plugs and Coil packs it seemed to have cured the misfire for about a week and now it's back. The car suffers from a lack of power in the lower revs until it reaches 3000rpm where the car seems to pick up and accelerate through the gears. I have noticed that in 5th gear and at a low speed, I think I can feel the car miss so I then drop into 4th, which cures the issue.

Do you think i have an issue with the actuator not working as it should?

regards
Jae
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I'm not a fan of guesses, but I'd replace the crankshaft sensor.
Mac.
 
A big thank you to everyone who has contributed so far.

A little update...
Had a couple of hours spare this afternoon so checked a few things.

MAF - I replaced the unit with a used unit supplied by Andy. Logged the readings on the airflow at WOT in 2nd gear and these were close to the original one, maybe around 5% lower. Also noticed that I generated another couple of fault codes with this unit fitted, 17912-Air intake system: Leak detected P1504 - 35-00 and 16955- Brake switch (F): Implausible signal P0571 - 35-00. I don't get these codes with the original unit fitted. Not sure whether to assume the replacement is faulty or whether there's an issue with the original that means these codes aren't generated. Either way it runs the same with either unit and I get the same misfire codes so for now I've refitted the original and ruled it out.

Pre cat lambda - carried out aging test and the numbers all look ok, period figure is 2.78 and status is B1-S1 OK. For now I'll consider that the pre cat lambda is fine.

Manifold flaps - Checked in block 142 and this shows them operating but not until the RPM reaches around 3300 rpm. Not sure whether that's a. an issue and b. likely to be the cause of my woes if it is. I can see the rod on the vacuum actuator moving and everything looks intact, so for now will assume the flaps are doing their stuff. I am wondering whether the flaps not moving until around 3300 rpm is a result of a loss of vacuum caused by a leak?

It's worth noting that after disconnecting the battery to reset everything the long term fuel trim has returned to 16.4%.

To my limited understanding of the system this is all pointing back to an air / vacuum leak, does anyone have any better ideas before I start taking things apart to physically check components?
 
I don't think there is a definitive rpm at which the flaps area deactivated, (they are activated, upward into air flow), at engine start. It is generally agreed that the change, (downwards, out of air flow), is around 2.800 rpm, and the power/torque curves support that. The movement is ECU controlled, by engine load and road speed so might vary if other parameters are not met, just a guess though.
No flap related DTCs, point to the flaps being OK, but the absence of miss fire at higher revs, points me in the direction of something related to the change in fuelling, timing, and engine set temperature. The thermostat opens early at high loads, running at 87/92C, at least that's what the ECU set point will be. Worth monitoring engine temperature set point versus actual.
Mac.
Edit: If the engine isn't reaching set temperature, (107/110C), at lower engine speed load etc, then maybe the ECU is fuelling on the basis it not running at the desired temperature.
Monitoring engine temperature set point versus actual might clarify this.
Mac.
 

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The misfire is present at higher RPM, just much less noticeable. From memory the misfire count does not increase proportionate to the RPM.
 
I took the undertray off to get a look at all of the oil filler and breather pipework hidden away underneath. I found quite a lot of oil around the level sensor in the sump and traced the source back to the oil separator on the back of he engine. Closer inspection suggests that the clip that connects the pipe assembly from the inlet manifold to it has failed, so possible air leak at the joint. Changing it looks very fiddly so I may try a temporary repair with some kind of semi setting sealant to see if that is the issue.
 

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So oil separator all back in with new o rings. Joining pipe still had clips intact so that went again with a new o ring.

I managed to find a good used EGR pipe, so that's now re instated with new gaskets.

No different, not even a little. Now giving up. Price reduced in advert, might break if enough interest but would prefer not to.
 
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