Hi all, 

 

After being in a workshop, the motor referred to above has developed a rough idle  once warmed up. I drove it to the dealer and on to the ramp. Once finished (cambelts), they test drove it and, surprised by the rough idle claimed to have run a diagnostic but found nothing. A Diagnostic check with a hand held scanner also shows no faults but the plugs look very different to normal, instead of the usual beige deposits I always see, the electrodes are coated with orange powder, the insulators completely white and the end of the plug body above the threads protruding into the cylinder itself a burnt black. The effect is identical on all four plugs. No fuel additives used. Driven on 95 octane petrol, occasionally 98. Fuel injectors all have c14.5 ohms resistance. An auto box and thus never driven hard. c110, 000 miles but consumes almost no oil. Oil changed 6 monthly but smelling quite strongly of petrol despite being  changed in March.

 

Once above 1000 rpm the unevenness smooths out and driving at speed is fine. No visible splits in any pipework around the engine bay and spraying brake cleaner round the engine (without effect) suggests that I'm not missing any. The dealer's staff have lost the rubber grommet that goes on the end of the pipe running from air filter to join the pipe from the brake servo to the manifold beneath the throttle body, however. The joint's obviously no longer airtight but I'm not sure how important that is, I assumed it's just intended to draw fresh filtered air in to the manifold at the point crankcase gases are introduced below the throttle body? That I've removed and there's no oil or carbon inside the manifold. I'm not able to see an EGR valve where there ought to be one but there's a PCV valve on the back of the block. No idea how that works. Coil packs were replaced as a group last year; ditto plugs. Lambda readings, though I'm not entirely conversant with their meaning, seemed low at idle: 0.97 something. Since I've owned it, fault codes for the manifold air pressure sensor have cropped up periodically describing an implausible reading though no change in performance correlates to them: they're cleared and don't appear for another 6 months or whatever.  

 

Apologies for the quality of the pictures. 

All suggestions received gratefully.

 

Martin.

23 minutes ago, gallaghermartinpaul said:

lost the rubber grommet that goes on the end of the pipe running from air filter to join the pipe from the brake servo to the manifold beneath the throttle body, however

Could you take and post a photo of this?  I'm not familiar with the breather arrangement on the automatic cars, so I'm not clear what exactly you mean, or what it does.

 

29 minutes ago, gallaghermartinpaul said:

Oil changed 6 monthly but smelling quite strongly of petrol despite being  changed in March.

 

That rings some alarm bells.  Has the coolant temperature sensor ever been changed to your knowledge? 

 

Later versions of the BKY engine had the EGR valve deleted from the design for some reason.  My recently acquired Polo has the same lack. Can't say I'm upset by the absence of something that seemed to cause a lot of problems on this engine family.

 

That spark plug does look odd, but I can't remember anything except additives causing weird colourations? 

Which oil does it get?

Hi, 

Thanks for the timely reply. I can only upload a couple of pics at a time it seems. These 2 should give an idea of where the pipe from the air filter box (the circled yellow end) runs to the manifold beneath the throttle body. As regards the rest: nope, coolant temp sensor was in place 5 years ago when I did the cambelts and not been touched since; the gauge sits dead on 90 and works quickly, coolant temp readings on a scanner are steady if about 5 degrees below what is shown on the gauge.

 

Oil is a 10-30 I recall, I'd used a 5 but it seemed to burn a little bit so I switched it. That was over 5 years ago, mind. Quality wise, I use a Liqui-Moly which here  (in Germany) is probably akin to the Halfords hi-end stuff, not the best but far from bargain-basement stuff. 

 

Thanks, 

Martin.

The air leak from the missing grommet is the problem, the spark plugs are a red herring.

That's annoying, no more uploads. The yellow circled end goes into the (standing looking over the engine) rear left-hand side of the engine cover/air filter box. From there it runs down a pipe internal to the box to emerge near the throttle plate. Apparently. 

So where isn't the grommet? At airbox end?

3 minutes ago, sepulchrave said:

The air leak from the missing grommet is the problem, the spark plugs are a red herring.

 

Thanks, it did kinda leap out at me when I spotted it today; mainly as it's the only tangible difference between now and when it went to the workshop. So it's allowing, what...too much unmetered air to the manifold? Weakening the mixture and raising the temp in the pots? Does that account for the funny colour? As I said, they've never looked like that before and I've had them out at least once a year since I owned it.

1 minute ago, Wino said:

So where isn't the grommet? At airbox end?

Yep. Other end is tight, sealed with an identical grommet.

6 minutes ago, gallaghermartinpaul said:

 

Thanks, it did kinda leap out at me when I spotted it today; mainly as it's the only tangible difference between now and when it went to the workshop. So it's allowing, what...too much unmetered air to the manifold? Weakening the mixture and raising the temp in the pots? Does that account for the funny colour? As I said, they've never looked like that before and I've had them out at least once a year since I owned it.

 

Yes, yes and yes.

 

Well, technically the air isn't unmetered it's just not under ECU control via the electronic throttle butterfly.

I still can't quite work out the function of that airbox hose. Is there a one-way valve in the airbox; to which it connects? Or a rather narrow orifice/jet?

Edited 25 June, 20205 yr by Wino

Looking at the photo it's the vacuum line running from the throttle body butterfly and it must be leaking horribly, there will be a non return valve downstream but that won't stop the engine sucking air when the butterfly is supposed to be almost shut at idle, hence the rough tickover.

Hi all, 

 

Having found and retrieved relevant grommet from where it was carelessly discarded in the wing, there's unfortunately no change.

 

Regarding temp sensor discussed yesterday, I assume it's working as unplugging it whilst running raises the rev range to c1000rpm and throws up a fault code.

Disconnecting the solenoid  for the purge line for the fuel vapours (which has an 11.7 volts feed) makes no difference and also generates a code. Removing fuse 7 which controls power steering and, in Haynes, 'engine electronics' makes no difference but no code thrown up.

 

I'm waiting 'til it cools down a bit and then thinking I'll check the first O2 sensor in the manifold and its connections. It has 4 wires going in, any idea off the top of your heads what the voltage should be? Also, whilst I remember, I noticed a couple of times that I couldn't get a good earth for the multimeter on the big earth points on the inner wings and had to go direct to the battery. Though there's no sign of other electrical problems, a clean surely can't harm them; would it affect the throttle body settings by cutting the power to them though?

 

Thanks, 

Martin.

I think if your car had an EGR valve, fuse 7 would be relevant to that.

Gotta walk the dog, do some work etc. but I'll come back to this later.

Are you sure the front oxygen sensor only has 4 wires, I'd expect 5?

 

 

Are you in Germany or Oxford at the moment?

Hi, 

In Germany, alas. Front Lambda removed there is, as you suggested, 5 wires: no. 6 black, no. 5: blue/black, no. 4: grey, no.3: yellow, no. 2 white. no. 1: blanked off. The plug at the end of the sensor's cable came apart with a gritty sound and was fairly grubby inside. Cleaned up, it now doesn't want to clip back together, the two halves join but there's a lot of resistance at the point you'd expect to hear it 'click' back together. There is also another smaller clip on the back of the main one (see pic). Oddly enough, running it in that state, i.e, sensor unplugged but me thinking it was connected, actually resulted in it running normally to operating temp. Thinking I'd sorted it, it was only walking round the back of the car that the smell of petrol alerted me to the fact that I hadn't. No dash warning light shown, but a code did come up when checked.

The ECU ignores the Lambda probe until the engine is up to temperature, only then will it attempt to run in closed loop mode.

 

Hence your accidental test results.

 

It is not possible to repair the probe, you should replace it if you suspect it is faulty.

I think actually sep, these wideband sensors start doing their job within a very few seconds of start-up (that's what my logging suggests anyhow).

The second sensor, after both cats, can compensate for duff/non-existent info from the first one, so will try to keep things on the straight and narrow as much as it can, which won't be enough for long in the complete absence of input from the first.

 

After getting the lambda connection to stay put, try running it without the cover/air filter fitted and see if symptoms change, there's a common fault that leads to the engine only being fed pre-heated air, which isn't good at this time of the year. Is the weather quite hot where you are Martin?

Thanks guys, 

 

Yeah, it's well into the 30's here. I have, however already tried what you suggest once the plug finally clicked into place: no luck. As everything's now a bit more accessible I thought about taking the (first) Lambda out and cleaning it. Is this likely to yield results, in your opinion(s)? I know from the almost-obsessively detailed service record that the car's first owner kept that neither have been changed. So at around 110,000 miles they're past the recommended interval. Much as I'm loath to start chucking parts at it randomly, having a dealer do something fairly similar will lead to a bill greater than the car's value in fairly short order. I'm assuming they're best done as a pair, the one just below the manifold and the other one downstream, beneath the car?

 

Thanks for your input thus far,

Martin. 

Its super-hot environment ought to be sufficient to keep it functionally clean.

No particular reason to replace as a pair, but I would hesitate to suggest replacement at all without much better evidence. You should see specific fault codes related to misbehaviours, and having just falsely thought I'd fixed one of our cars by doing just this, I am extra-wary. Expensive things too, usually. 

I thought you could check out the Lambda sensor with a voltmeter on the output signal wire.

 

I don't know which is which but think the wires would be - earth, 2 heater wires, power either 5v or 12v & signal output wire.

 

The voltage should swing around 0.5v ie 0.8v then 0.2v around once every 1 - 2 seconds.

 

If you give it throttle it should go high, then low on the overrun.

 

In your first post you mention Lambda 0.97 which would be rich, so the ECU will be trying to lean the mixture.

The plug certainly doesn't show a rich mixture.

Different for wideband sensors.

Every day is a school day 🙂

2 hours ago, Wino said:

I think actually sep, these wideband sensors start doing their job within a very few seconds of start-up (that's what my logging suggests anyhow).

 

Absolutely, I'm not suggesting the sensor isn't working, only that the ECU will ignore it until a certain temperature is reached because leaning the mixture cannot take place until fuel can no longer condense on the port walls, this isn't relevant on direct injection engines, only older port injection engines like ours.

I think - and this is based on older engines, with only 'narrowband' sensors - those voltages are wrong. There will be two wires for the heater (unless the heater gets its return through the exhaust). The heater wires could be of  a relatively heavy gauge, which should be a clue. Supply to the sensor will be via a resistor of maybe 1.6 to 2K Ohms back to the ECU. It is probably back to a 3.3 or 5 V supply. The two inputs to the ECU are possibly a little difficult to assess as the impedance is v. high, until the sensor is up to temperature (there will also be a resistor/current source which biases the voltage to somewhere defined, for fault detection purposes). 

 

Before the sensor is warmed up, measuring with a DVM is likely to lead to you measuring the fault biasing arrangements, rather than the sensor. What is sensed is the differential voltage across the sensor, and it should walk backwards and forwards either side of the set point.

A bit too technical for me, I have noticed that if the throttle is held down to a fast idle, say 1500 rpm, that oscillations of around 200 rpm occur. This is on a 2-3 second cycle and completely regular. No sign of obvious heater leads on the sensor, they're all the same gauge wire.

1 hour ago, PipH said:

Every day is a school day 🙂

 

You're not wrong. I wish I understood a hell of a lot more about how all this stuff works, in detail.

 

18 minutes ago, gallaghermartinpaul said:

A bit too technical for me, I have noticed that if the throttle is held down to a fast idle, say 1500 rpm, that oscillations of around 200 rpm occur. This is on a 2-3 second cycle and completely regular. No sign of obvious heater leads on the sensor, they're all the same gauge wire.

 

I can tell you the wiring details shortly, and some test info. Not sure there's much you can do beyond measuring heater resistance at ambient temperature (from memory of reading about it).

Here's the wiring:

 

Z19 is the integrated heater in the sensor G39. Continuous 12V goes onto one end of it at sensor pin 5 (blue/red), PWM controlled ground connection from ECU pin 5 to sensor pin 3 (brown wire) to heat as required to get desired temperature. 

I seem to remember the little external resistor (rectangle between pins 1 and 2) is some sort of 'select on test' tuning thing fitted as it's tested in the sensor factory. Lives under that cover that fell off yours I think.

Google will probably be able to tell you far more than I can about what the four thinner wires do.  Some current is varied by the ECU to keep something static, and the oxygen content can be inferred from the size of that current, is about the extent of what I remember.

 

Test instructions for heater resistance: -

 

At ambient temperature the resistance of the heating element
should be approx. 1...5 . The resistance increases
considerably even if the temperature rises only slightly

 

 

 

Edited 26 June, 20205 yr by Wino