My MPG has dropped low, on my usual trek down the M4, I can get 34+ @70+ MPH

It's now struggling to reach 30 MPG at 60 mph. At the same time it's still not boosting right with a pressure drop at peak of about 5 psi. Could the two be related ??

Boost has been on the blink for months, but hasn't really bothered me.

I'm now lucky if I can 28 mpg, rolling downhill in to Cardiff city centre, On a good run I could 35 before.

The maf was changed in about May IIRC, and the figure looks good when logged, CTS figures look good as does AIT both rising and falling as they should according to engine speed etc. Fuel trims are a bit wild though STFT +/- 10%, LTFT sat at -4.7% which indicates somethings not right. I've had a look at the O2 sensor readings but I'm not too sure what I should be seeing !!

Anyone got any input regarding O2 sensors ?? Or any other thoughts ??

Edit. No codes showing !!

Cheers

My MPG has dropped low, on my usual trek down the M4, I can get 34+ @70+ MPH

It's now struggling to reach 30 MPG at 60 mph. At the same time it's still not boosting right with a pressure drop at peak of about 5 psi. Could the two be related ??

Boost has been on the blink for months, but hasn't really bothered me.

I'm now lucky if I can 28 mpg, rolling downhill in to Cardiff city centre, On a good run I could 35 before.

The maf was changed in about May IIRC, and the figure looks good when logged, CTS figures look good as does AIT both rising and falling as they should according to engine speed etc. Fuel trims are a bit wild though STFT +/- 10%, LTFT sat at -4.7% which indicates somethings not right. I've had a look at the O2 sensor readings but I'm not too sure what I should be seeing !!

Anyone got any input regarding O2 sensors ?? Or any other thoughts ??

#

Edit, No codes showing !!

Cheers

On dual carriageway (with some hills) driving @ 60mph I have seen 38mpg, every year when it gets cold it drops down to about 34-35mpg,

"Fuel trims are a bit wild though STFT +/- 10%, LTFT sat at -4.7% which indicates somethings not right". Sorry thats beyond me.

Assuming you have checked all charge hoses / no manifold leaks, injectors ok?, airfilter is fairly clear?.

i automatically think map sensor

Air filter is OE replaced with MAF, the panckae pipe seems a little oily around the joints but looks ok to me. Dunno how to check injectors !!

Pipes aaround manifold look goos to, done S and Y pipes a few years back.

i automatically think map sensor

Any idea how too test it though ??

apart from replacement im not too sure,

the other boosting culprit is n75 valve

also the sensor in the inlet mani next to throttle body, gets just as dirty as throttle body itself, may be worth cleaning this very gently with something

also the sensor in the inlet mani next to throttle body, gets just as dirty as throttle body itself, may be worth cleaning this very gently with something

Figures are nice and steady though, rise and fall as expected, but got to be worth a try I guess as it takes seconds.

im back to n75 or map, in my mind tbh

also the wiring to each of these, there may be a break or a short causing the intermittent nature and getting worse.

Checked throroughly for boost leaks? Dump valve could also be to blame, the list never ends. With no codes it cooouuulllddd be likes of a leak or dump valve

Edited 16 January, 201313 yr by Lofty79

Any idea how too test it though ??

Ive had mine (maf sensor) apart to clean, its one of these "use it till it fails", you cant ajust anything. I would try unplugging the lead to it and giving it a squirt of electrical contact cleaner. Might be some crap on a electrical contact.

You mention oil on the pancake pipe hose, if you mean where it goes from s/steel to rubber hose held together by a spring clip, if there is a lot it might be worth changing the seal for the upgraded one. Last time I looked in that area there was'nt any oil residue.

To be honest you shouldnt really see any oil residue around any hose connections, unless you have taken it apart. Try tweaking all hose clips up a bit tighter (if you can).

Ive had mine (maf sensor) apart to clean, its one of these "use it till it fails", you cant ajust anything. I would try unplugging the lead to it and giving it a squirt of electrical contact cleaner. Might be some crap on a electrical contact.

You mention oil on the pancake pipe hose, if you mean where it goes from s/steel to rubber hose held together by a spring clip, if there is a lot it might be worth changing the seal for the upgraded one. Last time I looked in that area there was'nt any oil residue.

MAF or map, we are talking map here, yeah a little oil

See it around the join, not fresh looking though

your side plastics have snapped and dropped. Mines now gone from driving into a flood i didnt see.

I assume map as your maf was replaced

"To be honest you shouldnt really see any oil residue around any hose connections, unless you have taken it apart. Try tweaking all hose clips up a bit tighter (if you can)" (I was updating when you quoted lol). Looking at your pic cant really tell if its old or fresh.

Without error codes logged its going to be difficult to track down, I would do the inexpensive work first, checking electrical connections, as was mentioned earlier, wiring and hose connections, exhaust pipe leaking ?.

The N75 and its connections are worth investigating, is it the original and how many miles has car done?.

Finally how old are the exhaust sensors, I know they arnt cheap, but as a last resort if all else fails.

I did one O2 sensor a few years back, not sure which though, I think it was pre cat, when that went it popped the EML though, I've tried another N75 back in the summer(ish) whilst looking for the boost issue, You're right though I do need to check that boost hose.

Log your coolant temp sensor figure from cold to hot

Log your coolant temp sensor figure from cold to hot

I just watched it on the torque app, on the way home, stone cold start, climbs steadily up to 90, what am I looking for Clive ??

Vacuum hose split?

Checked the one under the mainfold at the front?

I would say an air leak,probably one of the pipes under the inlet manifold,seen in numerous times on 1.8 t,s.

yeah thats fine the if sits on 90 but i ould use vag com as im not sure ho accurate the torque app is

next up get it smoke tested for leaks

Cheers Clive, your up early lol

https://docs.google.com/file/d/0B1eiYmXOY7f0SnR5eTFYcHg0SGc/edit

Theres a link to the cold start log there, it's a biggie, how does lambda function look to you, if I got it right its doing an awful lot of correcting.

I think your right about torque too, the fuel trims swing widly in torque but in VCDS they are solid as you can see in the log, looks like its fine on idle but somethings not right throught the revs. To quote Rosstech

"The second field tells the fuel trim at elevated engine speeds (Multiplicative). Negative values indicate that the engine is running too rich and oxygen sensor control is therefore making it more lean by reducing the amount of time that the injectors are open."

So what causes the engine to run rich ???

work nights lol

need to look for leaks lots of correction going on!! will have a think when i get to work and will look at the log

Nice one clive.

Anything else I can log to look for clues. I'm thinking boost leak after the turbo

Just thinking out loud here.

I did some logs before xmas of the boost. Actual and specifed were all equal so I guess that means a leak would be after the turbo as the turbo is doing what it's asked.

Am I right ?