Poor fuel economy.

[Zaac]

My average fuel consumption reads a eye watering 33.2mpg over 388 miles which was a full tank.... It's a 1.9 130PD A4 B6

I've had the EGR valve off and cleaned that out and surrounding pipework but it's still shocking... On a run I can barely hit 42mpg on the onboard computer.

Fault codes are 0 there is none...

Now what!? Im stuck as to what to do next.

 

[S4_dan]

Get VCDS or find someone close to you that has it and run some logs and do some monitoring. It could be numerous thing affecting the mpg.

What are you tyre conditions and pressures like?

 

[Zaac]

Tyres are all near enough brand new..

Having looked around the forum I might have just made myself a few jobs...

The temp gauge never goes above 65 Degrees I did the temp sensor but no good so will try thermo..

Also in the engine bay on the left hand side theres a gap in the air box from the rad to about half way up the left hand side of the engine bay like a piece is missing so I bet the MAF sensor is all over the place.

 

[S4_dan]

Did you fit a genuine temp sensor? Non-genuine can cause all sorts of problems, including poor mpg!

The gap is possibly the air intake pipe to the air filter box that's missing. Shouldn't have much affect if any on the MAF other than warmer air being drawn in from the engine. Would need a pic to clarify.

Check tyre pressures, even if new. If over/under inflated this will affect mpg and handling but usually only by a few mpg at most. But worth checking and monitoring.

 

[Zaac]

Yeah it was a genuine one

The power delivery also is poor. It's a 130 remapped to 170 sometimes it's like a dart off the line and then when you want the power further up the gears its good but rarely... Most of the time its lumpy and slow.... Feels like it's got flat spots from 2-3.5k under acceleration that's why I had the EGR off and cleaned out when I had the cambelt done 2 weeks ago, also serviced etc.

 

[Mike.M]

Possible MAF issue or boost leak

 

[Zaac]

Does sometimes sound like a dump valve if I don't accelerate hard and left off at 2.5k ish

 

[S4_dan]

You need to get vcds on it in that case, monitor the maf and boost in some logs. I've just replaced my maf on my 2.5 but my symptoms weren't as bad as yours and my mpg was still pretty good. But the logs showed differently and was getting low readings from the maf.

You could try unplugging the maf and see how it drives then. I ran mine for a few months with it unplugged.

 

[Zaac]

Will unplugging the maf sensor cause any further damage? what will it do? will I see anything on my visual display like errors etc?

 

[Jimmy TDI]

If you unplug the MAF and it runs worse than it does now, then you know the MAF is fine.

 

[S4_dan]

As Jimmy said. But if it runs better then the maf is a likely culprit. No damage will be caused. The ecu will log a fault code but that is all. It won't affect anything even when the maf is reconnected.

 

[pauldazzle]

Don't think the unplugging the MAF trick works on Audi TDI's. Unlike VW & Skoda TDI's with the MAF unplugged Audi TDI's usually go into limp.
Logging on VCDS is the best way to check the MAF.
Sounds like you have a stuck open stat though.

 

[DieselJake]

Could always get it mapped out, one less thing to go wrong.

 

[AudiLeon]

Genuine Thermostat replacement is the obvious fix so far.

 

[Zaac]

I'm going to get the thermostat on later today fill up and run it empty and see what the results are after that (if obvcourse the engine temperature sorts itself out.)

 

[Icarus83]

I bit the bullet after seeing 72-74 degrees on my temp gauge since I bought the car last July, went to Audi and got OEM temp sender, thermostat, new rubber seals and temp sender clip (£68 from Audi for the lot). Fitted yesterday with new coolant, 90 degrees on the gauge now, spot on. Yet to notice a massive difference in economy, but mine is also a 130 mapped to 170 on the Revo Stage 1 map. Need a long run to see the difference I think. Will be replacing MAF next as its probably the original one on my car.......202k miles old.......

 

[Springer*]

Sounds like you may have solved your problem but one other thing that may be of concern is the dump valve type noise that you hear.

I used to have a VW Golf GTI PD150 that made exactly the same noise and shortly afterwards developed turbo problems. It turned out that the turbo was pretty sooted up and the vanes were sticking. The turbo spines were somehow rubbing against the turbo housing and this was causing a howling type noise that often sounded like a dump valve. There were also some boost leaks that caused the same sound.

Could be nothing in your case but worth investigating if the noise persists.

J

 

[Zaac]

I bit the bullet after seeing 72-74 degrees on my temp gauge since I bought the car last July, went to Audi and got OEM temp sender, thermostat, new rubber seals and temp sender clip (£68 from Audi for the lot). Fitted yesterday with new coolant, 90 degrees on the gauge now, spot on. Yet to notice a massive difference in economy, but mine is also a 130 mapped to 170 on the Revo Stage 1 map. Need a long run to see the difference I think. Will be replacing MAF next as its probably the original one on my car.......202k miles old.......

Mine's the same, 130 mapped up to 170. Waiting for thermo to be fitted then going to go from there

Sounds like you may have solved your problem but one other thing that may be of concern is the dump valve type noise that you hear.

I used to have a VW Golf GTI PD150 that made exactly the same noise and shortly afterwards developed turbo problems. It turned out that the turbo was pretty sooted up and the vanes were sticking. The turbo spines were somehow rubbing against the turbo housing and this was causing a howling type noise that often sounded like a dump valve. There were also some boost leaks that caused the same sound.

Could be nothing in your case but worth investigating if the noise persists.

J

Yeah thanks for that, it's not bad at all just when you ive it like minimal throttle and let off as the boost has spooled up but not given you any boost then you can hear it a little bit its the same on other cars so nothing to worry about also the past few days it's just been performing a lot better no nasty flat spots so going to do the sensors and then log some data on VAG COM and see what's happening.

 

[Greeny233]

Does sometimes sound like a dump valve if I don't accelerate hard and left off at 2.5k ish

Mine did this a while back and it was a split boost pipe. Pulled ok but just lacked that extra punch and sounded like a dump valve when i lifted off.

 

[DieselJake]

It's a sensitive engine and the real question about mpg is how fast do you drive and how long do you drive for, if it's short trips and/or like a rocket that's the problem.