Running rich / emissions problem

[937carrera]

My Polo Gti is very thirsty and an emission test shows high HC, High CO (6%+) and lambda of 0.85. There is no Check or EPC light illuminated and no stored error codes except for one relating to alternator output and another relating to sensor G277 which is not fitted to a Polo

I believe the car is simply overfuelling, the nose of the plugs look fine but the outer perimeter does look black

I have done the following in an attempt to resolve the problem, you may recall I have a spare ARC engine so swapping bits is relatively easy

Fitted a new Bosch rear lambda sensor (heater wasn't working, this was done before the test, as was a s/h cat swap as I damaged the flexi pipe removing the old sensor)
Swapped front lambda sensor for one which shows 1.0 when running
Changed/ cleaned MAP sensor
Changed injectors
Ensured fuel return pipe is clear
Looked for vacuum leaks from the throttle body, in the process remaking the connection to the brake servo which was split
Cleaned the throttle body
Swapped the throttle body
Checked cylinder compressions, all are in 12-14 bar range
Checked valve timing

In addition I have spent hours looking at VAG-Com. The readings for water temperature seem consistent with reality with water temperature of 90 degrees and a cold start idle of 1000 rpm which drops to 864 RPM when warm. In other words I don't think it's running in cold start mode

I have run the tests on the lambda system and have achieved passes on 033 036 and 034. The test on 046 starts if I get the cat up to around 380 degrees before starting the test but does not seem to get to completion. Looking at measuring block 031 I have lambda readings of just over 1.0

The only readings that seem to be unusual is that in group 033 the O2 sensor regulation seems to be around 25%, the cat temperature seems to be lower than I seem to be reading elsewhere at something like 280-350 degrees when stationary, depending on revs, and the result of the cat aging test 034 is 3.9 when a new one is only supposed to be 1.99 according to http://forums.vwvortex.com/showthread.p ... -converter

I have an old Gunson gas tester which measures CO. That gives a CO reading similar to the MOT emission tester

I haven't changed the plugs, but they don't look in bad condition and there are no misfires recorded in the ECU either

I'm struggling to think where to look next and don't want to continue putting unburnt fuel into my cat................. any ideas anyone ?

[alexperkins]

Is the charcoal canister and egr system working properly?

[937carrera]

I don't know......... never had to deal with those type of systems before and yet to discover how they work

[alexperkins]

How many miles are you getting to a tank of fuel?

[937carrera]

I'm not sure as I haven't done a proper check, at a guess, maybe 250 miles / 25-30 mpg ?

I've been reading around a bit. I don't believe the 6N2 GTi has an EGR system does it, but I can check the charcoal cannister

[937carrera]

I have located and examined the evap valve and filter housing.

I ran the output tests in vagcom and the valve could be heard / felt to be opening and closing. I repeated the test with the pipe to the throttle body removed and blew down the valve to ensure that he valve was actually opening, it was.

I tried to test the valve further in block 070, typical values were

Load 0%.......... Lambda 17.0%.......... Lambda -2.3%.......... Test Off

I could not get the test to commence. blipping the throttle allowed it to change to Test On momentarily as the revs died back to idle. Coolant was at 90 degrees, intake air temperature at 49 degrees

I have looked at the readiness codes. EGR, Oxygen sensor heating, aircon and catalyst heating are all OK Oxygen sensors, secondary air injection, evaporative emissions and catalytic converter are all failed or incomplete even though blocks 034, 036, 037 and 043 all pass

The only other thing I have noticed this morning is that the Check light does not illuminate when switching the ignition on, should it ?

[alexperkins]

The check light on ignition was added in later AVY blocks and some of the run out ARC blocks. Was mainly due to an emissions change requirement

[937carrera]

Ah OK, that's good to know, that's one thing less to fix.

Any suggestions on the testing of the evap system or the other results

[alexperkins]

It all looks normal

My GTI is pretty thirsty to be fair, but it passed its MOT so cant be that bad lol

Got a photo of the spark ends?

[937carrera]

Try these



The car has been on idle for quite a while. After calibration of the gas tester in air at 2%, CO is up at 6% with the Polo, but drops to less than 1% on my '97 Clio. On my air cooled VW it's around 3%

[alexperkins]

The sparks dont look too bad from the colour they are

Perhaps a little sooty as should be more of a browny colour

There isnt much left that you havent changed, unless the ECU is causing the overfuelling but I would find that unlikely. Either that, or the fuel pump is pushing too much fuel in

Is it running rough at all? Does it misfire? Do the fumes smell rich?

[937carrera]

The sparks dont look too bad from the colour they are

Perhaps a little sooty as should be more of a browny colour

Yep, that's pretty much what i was thinking

There isnt much left that you havent changed, unless the ECU is causing the overfuelling but I would find that unlikely.

I know, that's what's got me really struggling with this problem. ECU's generally don't fail either. Is there any way I can confirm it's the right ECU ?

Is it possible to erase the learnt values so mixture adaptation can begin again, perhaps it has needed extra fuel in the past becuase of some issue and that adaption is making the car rich now ?

Either that, or the fuel pump is pushing too much fuel in

Is it running rough at all? Does it misfire? Do the fumes smell rich?

I thought I had it figured out and that the fuel pump regulator was the problem. I have been told they generally fail low, rather than high, but swapped the regulator anyway, followed by the injectors (hoping a previous owner had fitted higher flow items). Neither made any real change

The car ticks over sweet as a nut. Sometimes when on the road, usually after about 5 minutes the car appears to have a misfire, revs drop, and then the car continues but with slightly reduced performance. When this happens full throttle accelleration is generally not much better than part throttle so i suspect it is choking. Ignition off/on will get performance back so it appears to be falling back to a conservative map, but not what I would call limp home mode.

The tailpipe does smell rich

[alexperkins]

Hmm this is an odd one

Normally fuel usage is dynamically adapted. I'd have to check ELSA for adaptation procedures.

Any errors whatsoever on VCDS?

[937carrera]

Yeah, i'll agree it is an odd one

Stored error codes are as below, there is no EPC / Check light illuminated

18002 - Camshaft Adjustment Oil Temp Sensor (G277): Short to Plus
P1594 - 35-00 - -
17911 - Load Signal from Alternator Term. DF: Implausible Signal
P1503 - 35-00 - -

18002 is a strange one as G277 is only fitted to Passats, from reading around other Polo owners have had the same error

17911 is being looked at, I'm rechecking resistances from the connector back to the ECU and dash; 0.4 ohms to the ECU seems reasonable

[937carrera]

I removed the ECU from the car for a few hours yesterday while I was tracing error 17911.

This has had the benefit of clearing error 18002 and all the learnt values for the fuelling.

I have taken the car out for a run and got the car nice & hot before taking it for an emissions test, as much as anything to make sure i still had a problem and my Gunson was not giving me false readings.

It's still very rich, on idle typical values were

CO 6%
HC 500+
Lambda 0.8

On fast idle the CO level rose to 8-9% and lambda dropped to 0.7

I now have some additional errors and the (new Bosch) rear lambda sensor is no longer passing the self test "B1-S2 Not OK"

16514 - Oxygen (Lambda) Sensor B1 S1: Malfunction in Circuit
P0130 - 35-10 - - - Intermittent
17584 - Bank1: O2S (Lambda) Correction Behind Catalyst: Control Limit Reached
P1176 - 35-00 - -

Much though I hate to simply swap parts over I'm beginning to think I need to try another ECU - (I should be able to match that to the car myself with Vagcom, shouldn't I ?)

Thoughts anyone ?