MK1 TT 225 MOT emissions fail help please.
Discussion
Oops, didn't see your other post. If it was a sensor unplugged though it would be surprising as it should set the engine check light on the dash.
Do you have to run it back for another MOT or is it a free re-test job?
p.s. Hope your oil pressure sensor was a genuine one, I replaced it on my 1.8T A4 from German and Swedish and within a few weeks had a large oil leak through the sensor electrical connector. Common problem with the cheapo ones apparently.
Coolant temp sensor is also common fail if you ever have trouble starting the car in cold temps, if it takes lots of cranking to start. Just in case you ever have that issue.
Do you have to run it back for another MOT or is it a free re-test job?
p.s. Hope your oil pressure sensor was a genuine one, I replaced it on my 1.8T A4 from German and Swedish and within a few weeks had a large oil leak through the sensor electrical connector. Common problem with the cheapo ones apparently.
Coolant temp sensor is also common fail if you ever have trouble starting the car in cold temps, if it takes lots of cranking to start. Just in case you ever have that issue.
Edited by Smiljan on Friday 12th March 12:59
So - MOT failure on emissions - slightly high CO and HC, low Lambda 0.87 something
temp happy at 90 degs
sits at idle (700ish rpm) perfectly - no issue.
accelerates smoothly, hits boost - all good.
NB - no VCDS faults
Symptoms - stationary, out of gear, warmed, engine RPM will not sit at (for example) 2k RPM. Accelerator pedal held rock steady, RPM rises by about 500, then falls back 800.
NB If I pull the plug into the MAF, I can hold RPM at 2k RPM
what has been done since MOT failure:
- an ECU reset by pulling fuse 37 for 10 minutes, then ignition on, no start, until the clicking stopped.
- MAF wires cleaned, gently with just the proper spray
- all (accessable from above) electric/sensor plugs pulled and cleaned
- all the hideous mess of pipework for the Activated Carbon filter system has been looked-at and no obvious splits - some slight cracking in some of the rubber sections *** but it could easily be pipework as I cannot see it all, nor can I inspect properly without taking it apart.
Been out for a spirited drive.
Now back home, no change - temp happy at 90 degs, stationary, I am trying to hold the revs at 'anything' rpm, and it won't, rising and then dropping off all by itself.
So - any steers on what is causing the rising-RPM, as this has to be connected to the out-of-range emissions?
Thanks!
temp happy at 90 degs
sits at idle (700ish rpm) perfectly - no issue.
accelerates smoothly, hits boost - all good.
NB - no VCDS faults
Symptoms - stationary, out of gear, warmed, engine RPM will not sit at (for example) 2k RPM. Accelerator pedal held rock steady, RPM rises by about 500, then falls back 800.
NB If I pull the plug into the MAF, I can hold RPM at 2k RPM
what has been done since MOT failure:
- an ECU reset by pulling fuse 37 for 10 minutes, then ignition on, no start, until the clicking stopped.
- MAF wires cleaned, gently with just the proper spray
- all (accessable from above) electric/sensor plugs pulled and cleaned
- all the hideous mess of pipework for the Activated Carbon filter system has been looked-at and no obvious splits - some slight cracking in some of the rubber sections *** but it could easily be pipework as I cannot see it all, nor can I inspect properly without taking it apart.
Been out for a spirited drive.
Now back home, no change - temp happy at 90 degs, stationary, I am trying to hold the revs at 'anything' rpm, and it won't, rising and then dropping off all by itself.
So - any steers on what is causing the rising-RPM, as this has to be connected to the out-of-range emissions?
Thanks!
I'd lend you my VCDS but I only have the 3 VIN version so don't want to use it on different cars.
You really need a scanner with live data to check the fuel trims and the 02 sensor outputs. Either you have some sort of air leak affecting the fuel mixture or there is a sensor issue causing the mixture to be incorrect.
Fluctuating revs when the throttle is held steady to me would suggest you may have an air leak at the intake possibly a split in one of the hoses. Unplugging the MAF just causes the ECU to use a set of predefined fueling values based on other sensors but ignoring airflow so may explain why the behaviour improves with the MAF unplugged.
The proper way to check the hoses is with a smoke tester but you can just go around and check them all manually one by one until you find the culprit. Some are hidden under the intake manifold so check those too.
The reason I suggested before you borrow or find a scanner or VCDS that can show live data is that you can watch the fuel trims short and long term and the 02 sensor outputs and immediately tell if it's a genuine fueling problem caused by external factors like a leak or if it's a dead sensor throwing off the measurements. If saves a whole heap of time and effort to do this before you spend hours hunting down a hose when that might not be the problem.
Have you done any work under the bonnet since the last MOT that may have disturbed a small hose or pulled one off, nicked it etc...?
You really need a scanner with live data to check the fuel trims and the 02 sensor outputs. Either you have some sort of air leak affecting the fuel mixture or there is a sensor issue causing the mixture to be incorrect.
Fluctuating revs when the throttle is held steady to me would suggest you may have an air leak at the intake possibly a split in one of the hoses. Unplugging the MAF just causes the ECU to use a set of predefined fueling values based on other sensors but ignoring airflow so may explain why the behaviour improves with the MAF unplugged.
The proper way to check the hoses is with a smoke tester but you can just go around and check them all manually one by one until you find the culprit. Some are hidden under the intake manifold so check those too.
The reason I suggested before you borrow or find a scanner or VCDS that can show live data is that you can watch the fuel trims short and long term and the 02 sensor outputs and immediately tell if it's a genuine fueling problem caused by external factors like a leak or if it's a dead sensor throwing off the measurements. If saves a whole heap of time and effort to do this before you spend hours hunting down a hose when that might not be the problem.
Have you done any work under the bonnet since the last MOT that may have disturbed a small hose or pulled one off, nicked it etc...?
Replaced the oil pressure sensor, but I shouldn't have damaged anything.
I don't have a scanner, but met up with someone who did - we did run a live VCDS scan, which is when we first noticed it wouldn't hold revs at 2k - but no fault codes.
Block 002 (MAF) engine idling
field 3 - between 1.0 and 4.0 = 2.something
field 4 - between 2.0 and 4.5 = 2.8 ish
Block 030 (Lambda) rpm 2000 *** slightly difficult to hold at 2000, it would climb very slowly then drop
field 1 - 111 fluctuating with 011 = yes it did
field 2 - 111 fluctuating with 011 = yes it did *** though it mostly sat at 110, I did see some 111/011
Block 034 pre-cat sensor
field 2 - >350 = yes it was 355
field 3 - >0.5 = yes but I don't remember exactly
field 4 - B1 - S1 - OK = no arrrrgh we didn't leave it long enough - still said 'Test off'
Block 036 post-cat sensor
field 2 - B1 - S2 - OK = yes it did
Block 037 both Lambda sensors
field 2 - 0.1 - 0.95 = yes 0.7 ish
CONCLUSION:
So apart from not waiting for the full test on pre-cat Lambda, what I missed was the other readings in block 037 damn.
I don't have a scanner, but met up with someone who did - we did run a live VCDS scan, which is when we first noticed it wouldn't hold revs at 2k - but no fault codes.
Block 002 (MAF) engine idling
field 3 - between 1.0 and 4.0 = 2.something
field 4 - between 2.0 and 4.5 = 2.8 ish
Block 030 (Lambda) rpm 2000 *** slightly difficult to hold at 2000, it would climb very slowly then drop
field 1 - 111 fluctuating with 011 = yes it did
field 2 - 111 fluctuating with 011 = yes it did *** though it mostly sat at 110, I did see some 111/011
Block 034 pre-cat sensor
field 2 - >350 = yes it was 355
field 3 - >0.5 = yes but I don't remember exactly
field 4 - B1 - S1 - OK = no arrrrgh we didn't leave it long enough - still said 'Test off'
Block 036 post-cat sensor
field 2 - B1 - S2 - OK = yes it did
Block 037 both Lambda sensors
field 2 - 0.1 - 0.95 = yes 0.7 ish
CONCLUSION:
So apart from not waiting for the full test on pre-cat Lambda, what I missed was the other readings in block 037 damn.
Edited by Orangecurry on Thursday 18th March 21:47
Can you get to this view on your version of VCDS? (Ignore the arrows)
You lambda reading is very, very rich so if the sensor is good you do have a fuelling issue.
Just out of interest how old is the fuel?
Lastly you sure that coolant temp sensor is good, if it’s stuck on a cold output value the car will run rich all of the time. Have a look at the live data for that as the car warms up. I know you say the dash temp reads ok but I’m not sure if there are 2 sensors or if the ECU feeds the dash gauge on these, worth checking since it’s the only thing you’ve disturbed.
You lambda reading is very, very rich so if the sensor is good you do have a fuelling issue.
Just out of interest how old is the fuel?
Lastly you sure that coolant temp sensor is good, if it’s stuck on a cold output value the car will run rich all of the time. Have a look at the live data for that as the car warms up. I know you say the dash temp reads ok but I’m not sure if there are 2 sensors or if the ECU feeds the dash gauge on these, worth checking since it’s the only thing you’ve disturbed.
Edited by Smiljan on Thursday 18th March 22:03
Smiljan said:
Just out of interest how old is the fuel?
Lastly you sure that coolant temp sensor is good, if it’s stuck on a cold output value the car will run rich all of the time. Have a look at the live data for that as the car warms up. I know you say the dash temp reads ok but I’m not sure if there are 2 sensors or if the ECU feeds the dash gauge on these, worth checking since it’s the only thing you’ve disturbed.
Fuel almost all new - I filled-up with 99 on the way to the MOTLastly you sure that coolant temp sensor is good, if it’s stuck on a cold output value the car will run rich all of the time. Have a look at the live data for that as the car warms up. I know you say the dash temp reads ok but I’m not sure if there are 2 sensors or if the ECU feeds the dash gauge on these, worth checking since it’s the only thing you’ve disturbed.
Hoses all hot, but I'll check again tomorrow - the VCDS didn't show any coolant temp sensor fault - no point in having VCDS if it doesn't tell you if a sensor is duff?
VCDS did know my EGT sensor had been unplugged in the past, so that's a good steer that VCDS is 'working'.
Fuel economy is good, so that's why I wondered if this combination of symptoms was an easy result - I've never had a rising RPM on a car before, but then I usually choose older cars with cables and less emission-preventing pipework!
Edited by Orangecurry on Monday 29th March 09:33
I did VW to death before I moved upmarket to sporty beetles.
Campaigns I had a Lhasa green one, and a Helios blue one
Mk2 16 valves I had a monza blue four headrest black leather interior one
And also a 1990 Scott’s of Sloane Square Oettinger in black,
I bought a 1987 caddy, and put an 1800 kjet mk1 running gear and brakes into it.
Vr6. Blackberry mulberry
And a Taro.
Nerrr.
Campaigns I had a Lhasa green one, and a Helios blue one
Mk2 16 valves I had a monza blue four headrest black leather interior one
And also a 1990 Scott’s of Sloane Square Oettinger in black,
I bought a 1987 caddy, and put an 1800 kjet mk1 running gear and brakes into it.
Vr6. Blackberry mulberry
And a Taro.
Nerrr.
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