VR6 poor fuel economy & performance

[ismith 0]

My 10 mile commute to work is only getting 25mpg (UK). I'd expect 30mpg from past experience of 10 years of being together now. Long distance is down some too.

 

The plugs are black but there are no ECU error codes logged.

 

The blue sensor was replaced a couple of years ago. With logging on VAG COM, it warms up beautifully in a sensible ramp from cold to 85C. The lamda readings start changing at 60.

 

The lambda was faulty once before and replaced and appears fine now - 0.95-1.05 on VAG COM when idling. The adaptation values seem to be weird though and change a lot: 0.626, 0.735, 0.891.

 

The injectors have been overhauled and I've tried a new MAF.

The fuel pressure is spot on (3.5 bar idling, 4.0 bar on throttle blip.)

 

My last track day left me behind a standard 2.0 litre mk2, so performance is way off.

 

Help!!!!!!!

[AlgarveVR6 0]

Know this might sound daft, but are you still getting your petrol from the same garage.

Sometimes from experience can make a hell of a difference. Other than this pearl of wisdom, I'm a bit stuffed to think what it might be

Dic

[martyjmcfly 0]

Hi there - next port of call is the G40 sensor, its only 20 odd quid.

 

I had poor performance, changed it and all fixed.

 

How recently was your lambda sensor changed. I had a new one fitted approx 1 year ago but due to a bodged plug repair emphasised by steam clean it knackered it. I was getting mid 25 mpg. Now shes back to normal :)

[zak 0]

i have similar issues with my vr, fuel consumption has gradually decreased in the 18 months ive had my car.

 

Whats the G40 sensor?

[martyjmcfly 0]

i think from memory its on the top of the engine and hidden by the plastics on the chains side, can't remember the part number but will have a look tomo if needed.

 

you loose about 30 bhp if its knackered. Crap fuel economy i reckon is lambda related

[boost monkey 0]

My last track day left me behind a standard 2.0 litre mk2, so performance is way off.

 

 

A mk2 golf? They didn't come with a 2.0l. Plus if they are 9A'd they're probably cammed too, and have a fair weight advantage (100-150kg)

[zak 0]

i think from memory its on the top of the engine and hidden by the plastics on the chains side, can't remember the part number but will have a look tomo if needed.

 

you loose about 30 bhp if its knackered. Crap fuel economy i reckon is lambda related

 

 

thanks i just had a search, i assume you are reffering to theCamshaft position (hall) sensor,i think i'll scan my car on vag com and see what it says

[dr_mat 0]

You did, of course, try an ECU reset and relearn?

[paul20v 0]

My 10 mile commute to work is only getting 25mpg (UK). I'd expect 30mpg from past experience of 10 years of being together now. Long distance is down some too.

 

The plugs are black but there are no ECU error codes logged.

 

The blue sensor was replaced a couple of years ago. With logging on VAG COM, it warms up beautifully in a sensible ramp from cold to 85C. The lamda readings start changing at 60.

 

The lambda was faulty once before and replaced and appears fine now - 0.95-1.05 on VAG COM when idling. The adaptation values seem to be weird though and change a lot: 0.626, 0.735, 0.891.

 

The injectors have been overhauled and I've tried a new MAF.

The fuel pressure is spot on (3.5 bar idling, 4.0 bar on throttle blip.)

 

My last track day left me behind a standard 2.0 litre mk2, so performance is way off.

 

 

lambda readings should fluctuate up and down the fact its .95 - 1.05 this should be going up and down from anything from .3 - 1v if on a graph the graph pattern goes up and down nearly a full 1volt in a regular pattern so if it is not moving as an actual value reading this would be your problem

[ismith 0]

lambda readings should fluctuate up and down the fact its .95 - 1.05 this should be going up and down from anything from .3 - 1v if on a graph the graph pattern goes up and down nearly a full 1volt in a regular pattern so if it is not moving as an actual value reading this would be your problem

 

Yes, the lambda readings fluctuate correctly. The ECU values go from 0.95-1.05, which corresponds to a sensible voltage. The weird thing is the range of ADAPTATION values for idle, mid and full throttle. This previously was 0.9xx-1.0xx, but now anything from 0.6 to 1.4.

 

What upsets this? Bad ECU, bad MAF wiring?

[dr_mat 0]

What upsets this? Bad ECU, bad MAF wiring?

 

Adaptation from bad components can cause this. So did you do the ECU reset and relearn or not?

[ismith 0]

Yes I did the reset and relearn.

[Tekara 0]

I've had the same problem for the last few months, mine has really struggled to achieve 25mpg, on long runs that can creep up slowly. Before i used to average 30+mpg with ease, and quite quickly from setting off. I've recently bought a brand new MAF which helped slightly, but hasn't returned the car back to its forma eco running.

 

I've spent ages looking at the settings in VAGCOM and performed numerous resets. I've noticed two slight oddities with the Lambda, one fault about "exceeding adaptation limit" was logged, then on another occasion i noticed the O2 values at idle were really erratic fluctuated from 0.85 - 1.2XX. After performing another reset and replacing the MAF the Lambda now seems to behaving its self reporting 0.95 - 1.08 at idle, but yet the poor fuel economy persists. I have tried driving around with the Lambda unplugged and the car behaved about the same the fuel wise, prehaps a smidge worse, but when reving the car felt so smooth.

 

Another observation with the fuel economy is it struggles to reach a high mpg no matter how carefully you drive it, but when having some fun with the right foot the MPG drops really quickly. Now before all my issues it used to be the opposite really quick to reach a good MPG, and quite slow to drop when booting it. So as not to rely on the MFA i used my old manual rule of thumb by looking at the needle, i used to be able to get about 200 miles per half tank, now that's down to around 170-180.

 

I should also note the temperature sensors have been replaced and the ECU water temp is about the same as the gauge, bar 1-3 degrees.

 

Can anyone offer any more incite before i go wasting money on replacing more parts. Could this all simply be Lambda related?

[zak 0]

where in vag com are people able to read the lambda sensor values? do you need a registered copy of vag com to access this info?

 

I bought a brand new lambda and blue temp sensor fromvw, should be fitting it over the weekend and i'll see if that makes a difference

[Tekara 0]

where in vag com are people able to read the lambda sensor values? do you need a registered copy of vag com to access this info?

 

I bought a brand new lambda and blue temp sensor fromvw, should be fitting it over the weekend and i'll see if that makes a difference

 

Cant say for definite, but im pretty sure you can view the values in the demo version of VAGCOM. You need to access the engine section, then go to measuring blocks, use the "up, down" buttons to select group 6, this displays all the learnt and live O2 values from the Lambda.

[dr_mat 0]

It's funny, we have threads like this every year around spring time... I wonder if it's not just the enormous cold start enrichment required for a 6-pot 2.9 in temperatures right down near freezing?

 

Stick the MFA in instantaneous mode (ignition on, press and hold button, ignition off, ignition on again, iirc) and see if it's *really* any different from normal once it's warmed up. The MFA's normal rolling average is taken over a long time, getting on to an hour or so.

 

Also bear in mind that with cold dense air you're getting more performance out of it, and that means.. using more fuel..

[zak 0]

i changed my temp sensor and done an ecu reset and there is no chnage, im going to try and change my lambda tommorow.

[zak 0]

vw gave me the wrong lambda so will have to wait untill next week untill i get it sorted

[ismith 0]

Anybody any updates?

[zak 0]

well i changed my lambda for a new genuine vag part and there has been no change to my fuel economy. But i still have not been able to do a proper ecu reset as i do not have a working version of vag com, pm me if anyon can help.

[ismith 0]

Just disconnecting the power for a few minutes and then doing the training sequence will get you close enough. The basic settings mode of the pay version of VAG-COM didn't seem to affect my economy, just ran things a bit smoother.

 

Even if you don't do a reset, the ECU will re-learn most of the way within a few hundred miles. If you're not seeing an improvement, we could be in the same boat!

[zak 0]

ive disconneced my battery after i changed the lambda but there was no difference, car is smooth and is pulling really well just the economy that is still an ongoing issue.

 

Ive never been able to get in to the basic settings in vag com, ive got another copy now so will give it a try and see if it makes make a difference.