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My 1.9 tdi 100 bhp averaging 30mpg? need advice


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#1 Regyboy

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Posted 09 January 2017 - 07:06 PM

Hi all, 3 days ago I bought a mk4 golf 1.9 tdi pd engine. I done a diagnostic and said coolant sensor, so replaced that and that's done, also I changed the fuel filter. I think it probably needs air filter, oil and oil filter done soon. took it to a mate who does m.o.t's he done the exhaust test and came up great passed emission test.

 

Do you think its just the dash giving me a wrong reading. or something else?

 

 




#2 Rob136

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Posted 09 January 2017 - 08:09 PM

a faulty coolant sensor would potentially cause poor mpg (real world and or indicated). Id get it serviced then see how far it goes on a tank, depending on driving style you should be seeing between 500and 600 miles to a tank with mixed driving. Also did you use a VW or at least a know brand temp sensor? Vws are known to be fussy with them and the cheap ones often don't last 5 mins.



#3 Regyboy

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Posted 09 January 2017 - 08:31 PM

a faulty coolant sensor would potentially cause poor mpg (real world and or indicated). Id get it serviced then see how far it goes on a tank, depending on driving style you should be seeing between 500and 600 miles to a tank with mixed driving. Also did you use a VW or at least a know brand temp sensor? Vws are known to be fussy with them and the cheap ones often don't last 5 mins.

 

its got a green end. its meant to be a good branded one I got from car spares. I did replace that and it didn't come back up on diagnostics. but don't understands why mpg isn't a lot better. hoping a service will show better mpg.



#4 gerrywac

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Posted 09 January 2017 - 10:26 PM

The dash mpg displays aren't renowned for their accuracy so unless you've had a chance to compare the gauge with the range over a few tankfuls range between fills is a better indication.

 

Suggest you follow Rob's guidelines on the range and if you haven't used an OEM (Bosch) sensor. You might keep an eye on temp gauge to see how long it takes to warm up. If the thermostat is stuck open the engine will take a long time to warm up and until it does mpg will take a battering.

 

You don't say what sort of driving your doing but although 30 is low if your doing short local journeys it's not going to get stellar mpg in the winter months.

 

I've a 1.9 Mk5 Tdi 105PS (had it 6 years) and know my display mpg is pretty accurate.On short local trips round town it takes a while to get to 30 (whilst the engine warms) and at the weekend on a 35mile round trip (couple of hour break)  of mixed town/urban A+B roads got 42mpg

 

Summer on long A+motorway high 50-mid 60



#5 Regyboy

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Posted 09 January 2017 - 10:47 PM

The dash mpg displays aren't renowned for their accuracy so unless you've had a chance to compare the gauge with the range over a few tankfuls range between fills is a better indication.

 

Suggest you follow Rob's guidelines on the range and if you haven't used an OEM (Bosch) sensor. You might keep an eye on temp gauge to see how long it takes to warm up. If the thermostat is stuck open the engine will take a long time to warm up and until it does mpg will take a battering.

 

You don't say what sort of driving your doing but although 30 is low if your doing short local journeys it's not going to get stellar mpg in the winter months.

 

I've a 1.9 Mk5 Tdi 105PS (had it 6 years) and know my display mpg is pretty accurate.On short local trips round town it takes a while to get to 30 (whilst the engine warms) and at the weekend on a 35mile round trip (couple of hour break)  of mixed town/urban A+B roads got 42mpg

 

Summer on long A+motorway high 50-mid 60

 

Hi, this is with me driving normal not even putting my foot down. I did find out the bush has gone on the wishbone so thinking is it down to that?



#6 Adam_Jonezy

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Posted 10 January 2017 - 07:26 AM

How many miles do you get to a tank full? Or even £20 worth? That will give you an idea on whether it is the display that is wrong or if your actually getting really pour mpg. 



#7 adam-

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Posted 10 January 2017 - 07:53 AM

Are you reading the right setting? Does it reset when you get into the car in the morning or does it say 30 straight away?

Are you driving around town? Start stop? Short journey? Engine up to temp? Motorway run? Thermostat failed? Did you buy a new genuine sensor?

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#8 TomasLT

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Posted 10 January 2017 - 08:23 AM

Do you idle for more than 5 min? When car idles, computer still counts mpg and it's hard to get miles when standing still burning fuel. Fill a tank, drive, count, it's the only true way.


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Edited by TomasLT, 10 January 2017 - 08:24 AM.


#9 szs

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Posted 10 January 2017 - 12:24 PM

I have had the same issue for a little while on my PD 130 and I am still learning about this issue so before you take my wordfir it, re-evaluate what I said.

Do you have access to VCDS? what coolant temperature does VCDS show?

Check for long term fuel trim on VCDS if it is anything above 5%, your car is running on additional fuel to keep the stoichiometric air/fuel ratio. This means you may have a vacuum leak and as such un-metered air is entering the engine and additional fuel is being added to compensate for the additional air hence poor mpg.

Do a smoke test for vacuum leaks.
Do check the exhaust for leaks before the oxygen sensor.

I am making my own smoke machine to test for vacuum leaks so haven't got to the bottom of it yet.

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#10 TomasLT

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Posted 10 January 2017 - 01:28 PM

Good points, except it's diesel, so pretty much they don't count, maybe vacuum leak, but not really, since it won't boost properly, that's noticable.


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#11 szs

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Posted 10 January 2017 - 01:47 PM

Good points, except it's diesel, so pretty much they don't count, maybe vacuum leak, but not really, since it won't boost properly, that's noticable.


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Which points? I thought these were applicable to both petrol and diesel? 😕

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#12 Regyboy

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Posted 10 January 2017 - 03:53 PM

Thanks for all the info guys, I've only had the car for 4 days. I've put £20 fuel in will see what I get to i. Be been driving it around town type of driving. So I expect Atleast 40mpg will service it soon see if it makes much of a difference.



#13 Regyboy

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Posted 10 January 2017 - 08:03 PM

I have had the same issue for a little while on my PD 130 and I am still learning about this issue so before you take my wordfir it, re-evaluate what I said.

Do you have access to VCDS? what coolant temperature does VCDS show?

Check for long term fuel trim on VCDS if it is anything above 5%, your car is running on additional fuel to keep the stoichiometric air/fuel ratio. This means you may have a vacuum leak and as such un-metered air is entering the engine and additional fuel is being added to compensate for the additional air hence poor mpg.

Do a smoke test for vacuum leaks.
Do check the exhaust for leaks before the oxygen sensor.

I am making my own smoke machine to test for vacuum leaks so haven't got to the bottom of it yet.

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How do I do a smoke test? And what is that? 



#14 szs

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Posted 10 January 2017 - 08:30 PM

How do I do a smoke test? And what is that?

In layman's terms, Stuff is burnt or heated in a container making smoke. Inlet of container is connected to an air source such as air compressor, outlet is connected to the car. The air forces the smoke through the car and the smoke comes out of any deteriorated piping, equipment etc. Which in turn highlights equipment that needs attention.

Google vacuum leak smoke machine. Loads of information on it including YouTube videos and you can make your own. I have almost finished mine. Can send you some pics once it's finished.

Important things to note is that you don't want the air pressure to exceed 2psi as this may destroy your pipes and you want to block the air filter/MAF so smoke can't reach it.

Hope this makes sense.

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#15 TomasLT

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Posted 10 January 2017 - 10:08 PM

Change all vacuum pipes to new ones, silicone or similar 5€ and 20min of work. Easier than smoke testing vacuum lines, which mostly isn't doable.

Szs, I mean what you described is for petrol engines, diesels doesn't have those parts or work the same way. So all of your tips doesn't apply.


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Edited by TomasLT, 10 January 2017 - 10:08 PM.


#16 adam-

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Posted 10 January 2017 - 10:14 PM

Important things to note is that you don't want the air pressure to exceed 2psi as this may destroy your pipes and you want to block the air filter/MAF so smoke can't reach it.


Good advice except that line. Pressure test it; so up to 30psi.

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#17 Airone

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Posted 10 January 2017 - 10:22 PM

Its winter all diesels use more fuel as the air is colder/more dense sor the ecu introduces more derv to balance, on a lighter note the car will be quicker...

 

 

 

Also the factor computer cannot be trusted for reliabe econamy results..

 

Tank drive tank is the only way.....



#18 Regyboy

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Posted 11 January 2017 - 08:56 PM

cheers all, well I put £20 of fuel in done 50 miles and plenty still to get. I think I had 16 litres to the £20 of diesel. so see what I get to ruffle 3 half gallons.



#19 Gti Fly

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Posted 11 January 2017 - 09:04 PM

Roughly speaking, u should get around 10 miles per litre ,

So 16 litres = 160 miles (give or take)


With just town driving it can be lower of course, but 30mpg is about worse as it'll go for town stop start crap

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#20 Regyboy

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Posted 11 January 2017 - 09:08 PM

Roughly speaking, u should get around 10 miles per litre ,

So 16 litres = 160 miles (give or take)


With just town driving it can be lower of course, but 30mpg is about worse as it'll go for town stop start crap

 

cheers, I'm mainly doing town stop start. hopefully I get better mpg than what the display says.



#21 Gti Fly

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Posted 11 January 2017 - 09:19 PM

Put it another way,

My fabia 1.9tdi 100bhp {remapped to 130bhp}

I've owned it for 8 years , it's now got 146000 miles , I bought it when it had 70,000 miles .


Best ever I got like 550-600 miles on a tank (40-45 litres)

The worse I got was 350miles to a tank , when all I did was use the car for 1.5 mile commute to work and home (so 3 miles a day) which involves about 30+ speed humps and give ways so the car barely goes into 3rd gear let alone past 30mph.

So 350 miles from 40 litres of the worse kind of driving , isn't far off 30mpg

<a href="http://uk-mkivs.net/...d-0-60-569secs/">Click for pics of my car</a>
Shoulda got a 150 tdi - everyone knows they are best..

 


#22 Regyboy

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Posted 11 January 2017 - 09:28 PM

Put it another way,

My fabia 1.9tdi 100bhp {remapped to 130bhp}

I've owned it for 8 years , it's now got 146000 miles , I bought it when it had 70,000 miles .


Best ever I got like 550-600 miles on a tank (40-45 litres)

The worse I got was 350miles to a tank , when all I did was use the car for 1.5 mile commute to work and home (so 3 miles a day) which involves about 30+ speed humps and give ways so the car barely goes into 3rd gear let alone past 30mph.

So 350 miles from 40 litres of the worse kind of driving , isn't far off 30mpg

 

how much did you have to pay for a remap? hoping to get one this year but don't want to go far from Birmingham to get it.



#23 Gti Fly

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Posted 11 January 2017 - 09:39 PM

R tech in hinkley is where I got mine done . I think it was 250 7 years ago

Rtech is the best man !

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Shoulda got a 150 tdi - everyone knows they are best..

 


#24 adam-

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Posted 11 January 2017 - 09:47 PM

Not for diesels he's not. He gets a sore head.

Also, fill the bloody tank. You've just bought a new car and you're doing start stop town driving. You'll be driving it harder than usual.

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#25 TomasLT

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Posted 11 January 2017 - 09:57 PM

My tank is 56l ?


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#26 Gti Fly

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Posted 11 January 2017 - 10:16 PM

Mine is 62

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Shoulda got a 150 tdi - everyone knows they are best..

 





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