Fuel is consumption on 6N2 GTi is worse than I expected and I have recently replaced the rear lambda sensor with a new Bosch one because the heating element was not working and the cat with a s/h cat because the flexi pipe was weak..

The only error codes in VAGcom relate to an "implausible" voltage from D+ on the alternator (cables check out fine) and a ghost error that relates to a sensor that is only fitted to a Passat.

I got an emissions test done at the weekend which showed a full house of high CO, HC and lambda at around 0.85. Not good.

Since then i have been spending lots of time looking at VAGcom readings and settings, swapped the lambda sensor and checked the vacuum pipes to the throttle body. The plastic pipe to the servo was split on one side at the connector so I cut and refitted that.

I dug out my old Gunson CO analyser to use as a diagnostic tool, if it reads within 0.5% that's good enough for observing improvement. I calibrated it to read 2% in air and then stuck it up the tailpipe and it read 5.6%. That was consistent with the garage tester at the weekend.

Here's some results from VAGcom

Anyone any suggestions as to what the different measuring blocks really mean or may be wrong ?

Temp 45 c ?? the engines not up to temp so the system wont be in full control, or the temp sensor is giving duff readings??

Cancel above !!

45c is the intake air temp. Lambda 0.8% is the altitude correction

have a look at group 007 and see if the MAP values are changing as you boot it?

I think the gauge was at 90 c, or perhaps I took the snap just after I had reassembled the car after checking the vacuum hoses.

Is item 3 of block 6 definitely water temp ? The fans had been coming on full speed for short periods and the lambda readings were consistent with the readings earlier anyway

Edited 15 July, 201412 yr by 937carrera

Have a look at www.ross-tech.com/vag-com/m_blocks/ it gives all the measuring block groups, If you can use the newer VCDS I'm sure it gives the value ranges below each block item, but I haven't used mine in a while to be sure of that fact

I have just fired up the car again. I have no values for measuring block 7.

Block 2 shows 296mbar absolute pressure on tickover which increases when the engine is accelerating and drops when the higher revs are achieved, i.e higher vacuum

Block 001 gives the water temp

Have a look at www.ross-tech.com/vag-com/m_blocks/ it gives all the measuring block groups, If you can use the newer VCDS I'm sure it gives the value ranges below each block item, but I haven't used mine in a while to be sure of that fact

Great link that Nige. I have now looked at block 31 and if I understand correctly that shows actual lambda of 1.24 against a specified value of 1.0039 at tickover. That lambda value is the inverse of what I expected to see though ??

Block 31 looks confusing ! it can show ether the voltage from each sensor or the actual & specified values?

I haven't done anything further on the car tonight, except for a bit of thinking, and you're right we don't know if the data being given is volts or lambda.

Trying to think what could be wrong and I had a thought that it might be a faulty MAP sensor. I feel a bit of a numpty for asking, but where is it located. I removed the throttle body from my spare engine and had a look around the intake but couldn't see anything that looked like it could be a MAP sensor ?

Do they go wrong often ? .

The MAP sensor is on the drivers side end of the inlet manifold (two torx screws) don't loose the "O" ring!! they do get gummed up with oil, so a spray with carb cleaner wont hurt! and it's also the inlet air temp sensor, and looking at your previous post it was showing 45c which does seem a bit high??

When my MAP sensor was playing up it didn't throw up any codes but it put the EPC light on !! removed it and sprayed it clean and it's been OK since :)

I've just been and run VCDS on my Ibiza I know it's not the same engine as yours but the control sensors are the same. Here's the log file of all the different measuring blocks, they start with the engine cold then I re-run them for the lambda etc when the engine had been running for 35 mins

You'll see the VCDS gives the suggested values for the different parameters unlike Vagcom

Log-X144RJC-152341.text

Thanks very much for taking the time to record & post that information, it was a great help.

I managed to find & swap the map sensor , AKA thrust sensor - no change (by the way what's the big thing on top of the cam cover on the right of the engine looking from the rear)

The main differences I found seemed to be related to lambda and voltages in blocks 31 and 33 so i swapped the front lambda sensor. The first points in measuring block 31 then changed from 1.23 to 1.00/1.01, and the second block in 33 from 2.04v to 1.58v, much closer to yours, so I think there was a lambda sensor problem. However, testing the exhaust gases showed CO still at over 5%,%2

That bit on the cam cover sounds like the VVT actuator

That second block in 33 has a normal voltage range of 0.000 to 1.500 so like mine (1.520) your at the top end of the range, but I'm getting an average of 51MPG on a steady 65 mph trip I don't know what my emissions are like as last month when it had the MOT they didn't bother to test it :) !!

hmmm, the %2 above was supposed to say something like

"so I don't think I have got to the primary issue yet.

If the lambda readings are to be believed, then is would seem that the oxygen content of the exhaust is about right, but with high CO (and presumably HC) then the car is still running rich. Could that perhaps be the the fuel pressure regulator providing higher pressure and hence more fuel than is required ?"

Well done on 51mpg by the way, I'll be happy if I get 40 !

A further update:

Today I have swapped out the fuel pressure regulator, throttle body and all 4 injectors. None of the changes made any difference. I have stared at VAGcom screens until I am the same colour as the screen and run the various tests, all of which passed except measuring block 046 which Icould not get to complete.

That doesn't leave very much else to check, save for the valve timing, which was suggested to me over the weekend as a possible cause. I have just removed the timing belt covers and turned the engine to TDC. Conveniently there are paint marks on the cam covers and crank toothed belt pulley which line up and are also aligned with the notch on the ancilliary drive belt pulley against the cam cover.

However, I don't think that the cam timing for the front camshaft is correct having looked in my Haynes manual (dangerous I know). It seems to be almost 180 degrees out of alignment

Could someone check the pictures below and confirm that the cam timing is either correct, or not, before I start further disassembly, ordering of parts and deciding how to make the special timing tool

Here's the camshafts

and a shot down to the crankshaft - not great I know, but you should be able to make out the white paint mark and perhaps the crank pulley notch

Here's some info

6N2 GTi Cambelt timing.doc

6N2 GTi Cam adjuster test.doc

Thanks, I was just looking for some more timing belt info and it seems there is a difference between the 1.4 DOHC and 1.6 GTi installations, which is why Haynes has a different image. At this stage mine still looks wrong though so I'll need to look in more detail when it's light again and double check I'm at TDC

Edited 21 July, 201412 yr by 937carrera

The Haynes doesn't cover the GTi engine, that's why I highlighted the GTi engine codes and the .doc files are from the dealer manual for the ARC/AVY/AJV

Looks like my looking in the Haynes manual for the 1.4 DOHC sent me down the wrong path. For the 1.4 the two timing holes are positioned at the closest point to each other. For the 1.6 GTi both timing holes are positioned to the left.

I rechecked the position of the crank and moved from TDC for number 4 to TDC for number 1, using a long screwdriver to confirm piston movement and the holes lined up correctly including the notch on the bottom pulley.

So the cam timing is fine and I'm still searching for the cause of the rich running

Here's what it should look like, note the use of an 8mm drill bit to replace special tool T10074

Edited 22 July, 201412 yr by 937carrera

A further update:

I was talking to a VW specialist recommended to me earlier today and he asked if I had done a compression test. When I said that I had and the cylinders 1-3 were 14 bar but number 4 was 12.5bar he suggested that it could be a poor seal on one of the valves and I should carry out a leak test. I did that, and because it had to be done cold the readings were worse than I was expecting, but most importantly were consistent across all 4 cylinders at 40-45%.

I have also replaced my crank sensor because there were intermittent problems being reported and the car was cutting out. The car seemed better with the new crank sensor and so I checked the CO readings again and was disappointed that they had not dropped.

As a random thought I decided to fit the original pre-cat lambda sensor which showed a lambda of 1.29 instead of 1.0. It still showed 1.29, but a CO check showed that it was down to zero.

I'm now getting error 16555 - Fuel Trim: System Too Lean: Bank 1 P0171 - 35-00 - - and the engine does not seem to tick over as smoothly and there seem to be minor pops/misfires when listening to the exhaust

I'll going to try and get another emissions check done tomorrow, could be interesting

In block 001 third window what is that reading, with the engine just started and then 20+ mins later when it should be closed loop

I have just popped outside & started the car - it's showing 25% lambda after 30 seconds running

I'll get the warmed up value in the morning

Just taken the car out for a run, box 3 is showing 0.0% on idle, I assume that means it's now operating closed loop ?

Block 030 shows 110 and 110

Block 031 shows 1.25-1.2930 actual against target 1.0039

Block 033 shows 0.0% and 2.06 voltage

Block 036 shows a steady 0.78v which increases to 0.82v on fast idle

I expected to see the voltage for s1 bouncing up and down around 1.5v and for s2 varying around 0.45v, is that correct ?

After taking the readings and being on idle for 10 minutes the cat temperature is 192 degrees

Edited 2 August, 201412 yr by 937carrera

Box 3 in 001 should be +/- 10% at all times mine went from +2.5% cold to -2.5% in closed loop

Have you checked ( I'm sure you have ) for any unmetered air leaks on the intake system? carbon canister valve leaking?

What was block 032 figures?

Block 031 should be 111 first 1 = probe heating ON second 1 = probe operationally ready Third 1 = 1 probe regulation active 0 = not active ???

Block 033 the voltage should be 1.4 ~ 1.6V and should be fluctuating around 0% but if its constant the lambda regulation has switched from regulation to control because there is a fault in the lambda regulation Voltage above 1.5V means a lean mixture detected

Cat temp should be at least 340 c

I have just come back from the emission check. Values are better, but it is still running rich !

CO ~ 2.5%

HC around 230

Lambda varying between 0.9 and 1.0, typical 0.96

Taking your points in turn

I seem to have either 25% or 0%, nothing inbetween

I have checked for air leaks and having fixed a dodgy connection to the servo cannot find any more. I have done the test on the Evap valve and it is pulsing correctly. If I disconnect the electrical connection, then that will simply seal closed won't it and eliminate the evap system from the engine breathing?

Block 032 is showing 0.0% for idle in box 1 and 9.8% when on fast tickover in box 2

Thanks for explaining the bit values. With the previous lambda sensor box 1 normally showed 111, the rear almost always 110, and that's a new Bosch lambda sensor

So block 033 is not giving anything like expected values. Can you explain what you mean by "regulation" and "control". I assume that is not the same as closed loop and open loop but another device through which attempts at providing lambda adjustment is aborther because of "out of norm" signals ??

I'm really struggling in reconciling the 2.06v / lean warning data from the ECU with the emissions test results. I've done around 50 miles today and i would say that my impression is that the car is running more economically than before, but probably not as good as it should be

Neither of the cats I have put on the car have ever seemed to run at 340 c unless I get the revs up to around 3500 rpm. Even when it's up ther if I let the car idle the temperature drops down to sub 200 c

I am going to swap over the S1 lambda sensor again and see what values i get. At least that's only a 10 minute job