FSI - Partial Fuel Trim too high?

Is it possible that the brake servo is at fault? Given that every other hose on the manifold is in good order. Stupid question but have you checked the breather hose going from the filler to the intake? Also the dipstick filler tubes both at the top and at the sump?

Edit: Could it be a valve not closing properly? Can you try an leakdown test on all cylinders?
 
Evripidis said:
Is it possible that the brake servo is at fault? Given that every other hose on the manifold is in good order. Stupid question but have you checked the breather hose going from the filler to the intake? Also the dipstick filler tubes both at the top and at the sump?

Edit: Could it be a valve not closing properly? Can you try an leakdown test on all cylinders?
Click to expand...
Or sticky lifters, as the AUA cylinder 2?
Mac.
 
Not tried a leakdown test, but compression was good on all. Might be worth a try.

Back to the flaps, tried adaptation, basic settings, 142 etc. Will show as Adp Run but won't complete. Actual showing as 92.5%. This doesn't look right. Visually the actuator rod moves as you would expect.

Any suggestions?
 
Stew, the flaps are vacuum-actuated on the a2 and I don't think that an adaptation will work properly without a vacuum source from the engine. In short, I don't think that you can make a correct adaptation (I stand to be corrected). But there is not much to adapt to as their positioning is either open or closed. If the vacuum is there the rod will move up and down and all that remains is the reported position.

There is a potentiometer on the flap shaft to measure their position and report back to the ecu. If memory serves me right, you can apply a vacuum on the flap actuator (suck on it) and observe the reported resistance value when open or closed. If there is little variance between the two endpoints then the potentiometer or the wiring must be the culprit. But, in such a case you would get an error code reporting so, e.g., set point not reached or similar.

If the rod is moving freely then I think your flaps are fine. No sexual pun intended!
 
Evripidis said:
Stew, the flaps are vacuum-actuated on the a2 and I don't think that an adaptation will work properly without a vacuum source from the engine. In short, I don't think that you can make a correct adaptation (I stand to be corrected). But there is not much to adapt to as their positioning is either open or closed. If the vacuum is there the rod will move up and down and all that remains is the reported position.

There is a potentiometer on the flap shaft to measure their position and report back to the ecu. If memory serves me right, you can apply a vacuum on the flap actuator (suck on it) and observe the reported resistance value when open or closed. If there is little variance between the two endpoints then the potentiometer or the wiring must be the culprit. But, in such a case you would get an error code reporting so, e.g., set point not reached or similar.

If the rod is moving freely then I think your flaps are fine. No sexual pun intended!
Click to expand...
Yes, you need vacuum for adaptation. The potentiometer has to see the full movement range of the flap spindle.
Mac.
 
Thanks guys.
I'm a bit baffled.
I put it on vagcom this morning and the misfires were all being counted on cylinder 1. I closed the measuring blocks then opened them again about a minute later and the misfires had mysteriously moved to cylinder 4. I didn't stop the engine, it was left at idle. I guess this should rule out anything cylinder specific?
 
stew said:
Thanks guys.
I'm a bit baffled.
I put it on vagcom this morning and the misfires were all being counted on cylinder 1. I closed the measuring blocks then opened them again about a minute later and the misfires had mysteriously moved to cylinder 4. I didn't stop the engine, it was left at idle. I guess this should rule out anything cylinder specific?
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Agree, that's logical, (as well as being illogical, if you see what I mean).
I'm still wondering about the crankshaft sensor, as it governs when the spark is triggered, and flags the misfire if the bang doesn't come at the right time. It controls fuel injection, and is a parameter in many things like camshaft adjustment.
It is the key single component that controls almost everything in the engine.
It's easy to find in VCDS, it's Group 1, Block 1!
It comes up many times in other groups. Not sure what the block shows, but got to be worth a look. An oscilloscope would be ideal to check it out. But, not something you'd have in your toolbox.
Mac.
 
PlasticMac said:
Agree, that's logical, (as well as being illogical, if you see what I mean).
I'm still wondering about the crankshaft sensor, as it governs when the spark is triggered, and flags the misfire if the bang doesn't come at the right time. It controls fuel injection, and is a parameter in many things like camshaft adjustment.
It is the key single component that controls almost everything in the engine.
It's easy to find in VCDS, it's Group 1, Block 1!
It comes up many times in other groups. Not sure what the block shows, but got to be worth a look. An oscilloscope would be ideal to check it out. But, not something you'd have in your toolbox.
Mac.
Click to expand...
I agree that's definitely worth a look. I've always assumed they either work or they don't but that's just an assumption.
I'll let you know what I find...
 
stew said:
I agree that's definitely worth a look. I've always assumed they either work or they don't but that's just an assumption.
I'll let you know what I find...
Click to expand...
I believe you should see a nice clean square wave coming out of these sensors. I’m not sure if the trigger is the leading or trailing edge of this wave. If it’s not a clean square wave then both the leading and trailing edge will be ’distorted’ leading to variance in the trigger which I guess could lead to the fire signal to the plugs being less than precise

J
 
birtyA2 said:
I believe you should see a nice clean square wave coming out of these sensors. I’m not sure if the trigger is the leading or trailing edge of this wave. If it’s not a clean square wave then both the leading and trailing edge will be ’distorted’ leading to variance in the trigger which I guess could lead to the fire signal to the plugs being less than precise

J
Click to expand...
It's a Hall Effect semiconductor sensor, so should be nice and clean. Do you have a 'scope about your person perchance?
Mac.
 
No scope I'm afraid. Maybe just as cost effective to replace. I'm wondering whether something was disturbed when I changed the timing belt? I'm assuming the sensor is in the vicinity of that end of the crank?
Have also noted a new code regarding signal from brake light switch. Would that be relevant?
 
stew said:
No scope I'm afraid. Maybe just as cost effective to replace. I'm wondering whether something was disturbed when I changed the timing belt? I'm assuming the sensor is in the vicinity of that end of the crank?
Have also noted a new code regarding signal from brake light switch. Would that be relevant?
Click to expand...
The brake light switch seems to have implications far beyond the brake lights, and has popped up as a possible cause of many faults, many times. Use only genuine, and follow the instructions to the letter.
Mac.
 
If your multimeter can measure frequency then you can probably get a reading off the sensor by probing the pins while the engine is running. If there is a constant-ish reading for stable rpm then probably is ok. Tricky but it can give you a heads up. Depending on the number of teeth you can work out the expected frequency. Probably this is mentioned in elsawin but I haven't got access at the moment.
 
PlasticMac said:
It's a Hall Effect semiconductor sensor, so should be nice and clean. Do you have a 'scope about your person perchance?
Mac.
Click to expand...
Hi
In theory my multimeter can do it but haven’t tried. If I get a moment this weekend I might give it a try.
J
 
stew said:
No scope I'm afraid. Maybe just as cost effective to replace. I'm wondering whether something was disturbed when I changed the timing belt? I'm assuming the sensor is in the vicinity of that end of the crank?
Have also noted a new code regarding signal from brake light switch. Would that be relevant?
Click to expand...
No worries I was just thinking about how it works in theory and how if the output was not nice and clean it could in theory cause some issues. It might be worth cleaning the connector as a no cost option before thinking about changing

J
 
stew said:
No scope I'm afraid. Maybe just as cost effective to replace. I'm wondering whether something was disturbed when I changed the timing belt? I'm assuming the sensor is in the vicinity of that end of the crank?
Have also noted a new code regarding signal from brake light switch. Would that be relevant?
Click to expand...
Yes at the end of the crank at the gearbox end on the bottom back hidden under a protective rubber shield. I once located it for a FSI member, struck me as a pig to work on and expect to work by feel.

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Andy
 
Brake light switch not working. The switch itself functions fine but the body has worn so its loose in its mounting. New one on order.
 
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