WTF is going on with my car...

[muddyboots]

For a good few weeks now, my MPG has dropped quite dramatically (MFA is showing an average of 39.8mpg now ), and the engine performance feels different - feels flat at low revs then comes really alive as I get nearer 4k.
These are very noticeable differences.

On Friday, I drove somewhere local and noticed the car "felt different", it felt more eager again at lower revs. On Saturday we did the usual trip to the mother-in-laws, and my economy had perked up again almost back to previous levels (this is a route I've driven many times).

But today it felt flat again, mpg had dropped again, and to cap it all it there is now a noticeable amount of smoke under hard acceleration, which wasn't there before.

Puzzled now. For a long time it's made a hissing noise - audible from inside the cabin - as I accelerate and engine revs rise, but I'm buggered if I can find where it's coming from.

Wondering if it's a suspect MAP sensor or some other obscure problem...

 

[driveforward]

Is this since you started using the new Millers additive?

 

[EdButler]

It could be a dodgy MAF Muddy, thats what initially came to mind? Mine has seemed to dip quite a lot lately when it should be increasing due to the warmer weather, but it definitely still pulls like a train.

If its the MAP it should throw up an error or at least a quick log on Vag Com on your way to work could exclude it.

Id just log all the usuals - Boost, Boost temps, MAF, Injectors and pop them on here.

 

[Niall]

I would check all conections of the intercooler pipes, a dodgy o-ring can cause obscure problems.

Further check fault codes, possible injector wiring?

 

[muddyboots]

There have never been any fault codes.

I think the boost pipework connections are the next target. I've already replaced one metal clip that I found had one of it's lugs missing, and fitted a new O-ring at the same time, but that made no difference.

I did wonder if it was a vacuum leak somewhere, but I replaced all the original flexible vac pipes with silicon hose, and last week I pulled various hoses off and I could build up a reasonable amount of vacuum in them, which seemed to maintain OK.

Ian -> I started using the new additive after the problems started (not long after though). No harm in running a tankful or two without it though just to make sure.

 

[craig-pd130]

Just a thought -- I know your Passat's vac plumbing is a bit different to mine, but do you have a plastic sphere, about the size of a softball, somewhere on the system?

Mine's just in front of and under the turbo, it's supposed to be a "vac accumulator". Wonder if that's got a leak?

 

[muddyboots]

Yes they all have the vacuum accumulator somewhere. I did give it a good hard suck the other day, it maintain vacuum and I couldn't hear any leaks.
The VNT actuator valve is right next to it, both very hard to get to. Can see better from underneath with the engine tray off, but still hard to get hands to even from underneath.
Ours should be the same, except for my lack of EGR vac pipes
Just remembered - when I had the inlet pipe off the turbo the other day, I stuck the camera down to take some photos of the turbo inlet vanes, bit sad I know but I bet some would like to see them...

I reckon I must still have a boost leak somewhere. The hiss that it's always made definitely isn't normal...given that I can hear it from the cabin it must surely be around the plastic pipework running round the rear of the engine, coincidentally this is where the MAP sensor is.

 

[Red ibiza]

Yes lets see the pics Muddy!

Wouldn't do any harm would it to clean the MAP sensor, bet its got a good covering of oil on it.

 

[Topsey]

I had loss of power, mega dip in fuel ecomony and black smoke with my previous car - a Passat TDi (55 plate) - though it was a "Friday afternoon" car!
The first time it was a split turbo booster pipe, 2nd and 3rd times (yes, really) it was a faulty fuel temperature sensor. Every time the emissions light didn't come on for absolutely ages but I knew something was wrong.

 

[Nathanio]

Sounds like a poss leak to me! Have you tried a ECU reset? Tried replugging the MAF?>

 

[muddyboots]

I had loss of power, mega dip in fuel ecomony and black smoke with my previous car - a Passat TDi (55 plate) - though it was a "Friday afternoon" car!
The first time it was a split turbo booster pipe, 2nd and 3rd times (yes, really) it was a faulty fuel temperature sensor. Every time the emissions light didn't come on for absolutely ages but I knew something was wrong.

Thanks for that, hadn't considered the fuel temp sensor...can check that with vag-com.

Cheers (also from Derbyshire!)

 

[muddyboots]

BTW Topsey - do you know which pipe had split on yours ?

 

[muddyboots]

OK - this morning I logged engine blocks 003 and 007 over my whole 1 hour 10 minutes journey to work. I know there are plenty of other blocks to log as well, but this is a start.

Parameters logged:

Engine speed (rpm)
MAF (specified)
MAF (actual)
EGR duty cycle - ignore this though, EGR is disconnected
Fuel temp
Fuel cooling state (100% means ON, 0% means OFF)
Intake air temp
Coolant Temp

Logfile: http://www.seat-ibiza-mk4.co.uk/files/LOG-01-003-007-xxx-13-03-2007.csv

It's a whole mix of driving. It started logging within a few seconds of starting from stone cold, with the engine idling for a short while before moving off. It was approx 3-4º degrees outside.
There's a sustained 28-second full-power run through the gears between timestamps 1993 - 2021 (rows 2435-2471 looking in Excel).
(Ed, remember where you met me on the way to Awesome, well it's the dual carriageway section that starts about half a mile or so from there )

A few points:

Despite the car having sat all night and it being only 3-4º degrees ambient, the fuel temp sensor readings begin at 14.4º - IE about 10 degrees higher. I started logging less than a minute from starting the car, I don't think it warmed up 10 degrees in that time... I wonder if this is significant enough to cause any problems?
Has anyone else ever logged fuel temp from a cold start to see how closely it matches the ambient temps ?

On a similar note, I notice the coolant temp starts from 25º. However there was a small time between starting the engine and beginning logging, maybe the electrical coolant heater had already got it this warm in that time. Within the first two minutes of logging, it rose by a further 15º...
Think I need to try again tomorrow from cold, but start logging immediately the engine is running.

After a 28 second uphill full-power run in a remapped 130, I thought a max intake temp of 47.7º is pretty good going for a standard SMIC, lower than the Ibiza would have been. Obviously pretty cool outside but in warmer weather I've never seen it go above 60º.

Ignore the EGR duty cycle, EGR is disconnected.

Fuel cooler seems to switch on when fuel temp reaches 70º. On the Passat there is a separate water cooling circuit to cool the fuel, there's a small rad just behind the driver's side foglight.

 

[Wheely]

I am following this real closely Muddyboots............as you know my Leon Cupra TDi economy dropped off pretty much the same time as yours.

Now mine seemed to be on the weekend that I got all 4 tyres changed (for same brand) AND did my first single shot of millers additive.

Since then I have

1. Double-shotted Millers - no difference
2. Used a decent fuel - BP Ultimate Derv (or watever its called)
3. Replaced a grotty looking air filter
4. Had its 30K service (which includes a vagcom basic faultcode check)

But STILL seeing on average around 5 - 7 mpg less than it was before that weekend.

I have even wondered if the garage that fitted the tyres (and I left them alone for an hour) have swapped a part ?!?!?!?!?! (unlikely but u never know).
I also wondered whether the Millers has removed a bit of sludge/deposit pre-injector which has re-deposited around an injector ?!?!??

I havent verified this, but I believe my symptoms are more noticable the more I granny it. That means if I hoon it my mpg is more like it was, but when taking it easy I cannot reap those mpg rewards.

Car is still under warranty until July, so like to find something amiss.

Any ideas ??? (I havent got vagcom)

 

[Topsey]

BTW Topsey - do you know which pipe had split on yours ?

no, sorry - it was a company car and the dealer (in Burton on Trent) told me very little, only that it was a split turbo booster pipe. Model was 1.9TDI (100bhp) if that helps. The symptoms were poor fuel economy and inability to get up hills!

When then fuel temperature sensor went, it was like something went "pop". The mpg went through the roof at times and the revs were a lot higher. No lights came on until my dearly beloved put something on the engine to "make it go better or show up a fault". Then the emissions workshop light came on within about 20 miles.

Sorry can't be of more help.

 

[EdButler]

(Ed, remember where you met me on the way to Awesome, well it's the dual carriageway section that starts about half a mile or so from there )

Yup! Perfect peice of loggin' road!

Well your MAF looks pretty healthy - heres yours against mine... Yours does seem to die off a bit at 4250+ though although mine is a phase two. That dip at 2k seems a little more dramatic too.

Ill have a look at my fuel temps tonight for you mate. I reckon you should log boost tomorrow though, those fuel temps dont look too suspect as the compression of the pump should effect them pretty instansaneously.

 

[muddyboots]

Thanks Ed.

Ill have a look at my fuel temps tonight for you mate. I reckon you should log boost tomorrow though, those fuel temps dont look too suspect as the compression of the pump should effect them pretty instansaneously.

Ta - best if you can log from a stone-cold startup (ie first startup in the morning) if that's possible !

 

[muddyboots]

Actually - just thought, you should be able to log the fuel temp before the engine is actually started up.

 

[thebeno]

I am following this real closely Muddyboots............as you know my Leon Cupra TDi economy dropped off pretty much the same time as yours.

Now mine seemed to be on the weekend that I got all 4 tyres changed (for same brand) AND did my first single shot of millers additive.

Since then I have

1. Double-shotted Millers - no difference
2. Used a decent fuel - BP Ultimate Derv (or watever its called)
3. Replaced a grotty looking air filter
4. Had its 30K service (which includes a vagcom basic faultcode check)

But STILL seeing on average around 5 - 7 mpg less than it was before that weekend.

I have even wondered if the garage that fitted the tyres (and I left them alone for an hour) have swapped a part ?!?!?!?!?! (unlikely but u never know).
I also wondered whether the Millers has removed a bit of sludge/deposit pre-injector which has re-deposited around an injector ?!?!??

I havent verified this, but I believe my symptoms are more noticable the more I granny it. That means if I hoon it my mpg is more like it was, but when taking it easy I cannot reap those mpg rewards.

Car is still under warranty until July, so like to find something amiss.

Any ideas ??? (I havent got vagcom)

Would I be completely stupid to suggest that your new tyres could be so good ie so much stick that they actually increase friction?

 

[EdButler]

Actually - just thought, you should be able to log the fuel temp before the engine is actually started up.

Yep! Ill do that. Need to clear the airbag light off anyways