VR6 fuelling & lambda issues

[Serial 0]

I've got a few issues with my VR6, hopefully someone may be able to shed some light on what may be the problem.

 

In general it runs pretty well - starts on the button, pulls well throughout the rev range. However recently the mileage dropped off quite a bit (was getting ~36mpg indicated on steady motorway runs, now it's more like 32-33 at the very best) and it's developed a noticeable pinking between 3000-4000rpm under load.

 

So, I went for a drive at the weekend, hooked up to VAG-COM and logged a few bits of data.

 

Three things seem wrong to me:

 

Firstly, the lambda adapted values look wrong, shouldn't they be closer to 1.000?

 

O2    Idle            Part Throttle   Full Throttle
Active  Adapted Value   Adapted Value   Adapted Value

1.195   1.109           1.055           1.203

 

So I plotted the O2 Active reading and it basically never goes below 1.000:

 

[ATTACH=CONFIG]49064[/ATTACH]

 

If I'm right, that value should be fluctuating either side of 1.000, and should average about 1.000. It averages 1.065,and only 85 out of 1128 readings are below 1.000.

 

Finally, I got this error code:

 

00537 -  Lambda (Oxygen Sensor) Regulation


       08-10 -  Control Limit Surpassed - Intermittent

 

So I guess the question is, is that the lambda probe that's at fault, or could something else be preventing the reading going below 1? Maf?

[Serial 0]

Hi, I wonder if anyone can tell me what the lambda readings above might mean? Does O2 Active > 1 mean lean or rich mixture?

 

I started the car today and it was really lumpy, definitely firing on only 5 cylinders, then after 30 seconds or so it was running fine... Possibly a sticky injector??

 

Thanks

[RW1 0]

If Lambda is greater than 1.0, then there is a surplus of air and the engine is running lean. If Lambda is less than 1.0, then there is a surplus of fuel and the engine is running rich.

 

Look for an intake air leak after the MAF. Extra air getting in.

 

Or sticking closed injector. Not sticking open.

 

Those 2nd, 3rd & 4th stored values suggest it is more than just at start up issue, so air leak. Good place to start with is the curving duct after the MAF, ahead of the throttle body, hairline split.

 

.

Edited September 17, 2011 by RW1

[Serial 0]

Thanks RW1 - I'll take a look at the intake as you suggest. Looking at the graph of the 02 Active reading, intermittently it has good readings so I'm thinking it might be dodgy injector or injector wiring. Looks like a loom refurb and injector servicing is on the cards as well.

 

Cheers

[RW1 0]

it's developed a noticeable pinking between 3000-4000rpm under load.

Under load suggests the engine moving to open up a leak, that why I wrote look at the curved duct ahead of the throttle body.

 

Don't think injectors. Look at the plugs and their colour. Generally all the same?

 

Also if no airleak in the intake post the MAF to the engine, it maybe the Lambda is on the way out. They don't last for ever.

 

I'd check the Lambda cable loom from the rear engine mount to the cat. Particulalry at the cat end where the wires enter the probe for a possible wire almost broken. Again under loaf the cat will move, and so the probe relative to its wiring loom.

 

.

[toyotec 0]

The adaptation ( long term) occurs over a certain amount of cycles and operate in addtional mode for idle, muliplicative for part load.

You also have general lambda regualtion that would wobble the fuel mixture between 0.97 to 1.05 lambda for best cat efficiency. If a disruption to lambda 1 occurs, like an air leak or dodgy injector, the lambda controller will add or remove fuel.

 

You car seems to be running lean as the lambda controller is adding fuel by up to 20% in the long term. 25% is usually the clip for both the short term and long term items hence the fault. The 02 reading relates to general lambda control. Nominal values are +/- 3%.

I would look at items such as the purge valve as with age these can stop sealing or seating leading to a throttle bypass and messing up the aircharge calculation.