TDi75 VS TDi90

nimz365

New Member
I have recently purchased a Tdi90 in addition to my beloved TDi75. I have noticed a marked difference in the diesel consumption!!! The 90 is loads more thirsty than the 75.

Is this normal?

How can i make the Tdi 90 more economical i.e. engine remapping, gear ratios, reduce the power?? can this even be done?

Anyone know where I can do it, if its possible ?

Also the 90 is making a hissing noise when I accelerate. Is this the turbo or air suction? its worrying as the 75 does not do this, is it normal?
 
i have a 90 and a 75 sport. havent noticed much difference in mpg tho. the 90 is doing 55.5 now the weather has warmed up a bit. thats with me trying my best.

iv always envied those who say they get 60+ perhaps i need economy lessons or A2 driving lessons!

not used my 75 much as im intending selling the 90 soon but it was doing around the same mpg 52 -53 a few weeks back.

perhaps yr 90 needs a service? what mpg are you getting from both cars?
 
The 90 is more thirsty than the 75 in the real world although Audi's predicted figures were very similar at the time of production. I feel the main reason is that the 90 encourages you to accelerate harder as it's more lively so it will be revving higher most of the time especially when you are pulling away through the gears which obviously in turn uses more fuel.

Regarding the hissing sound it could be a leaking boost hose leaking out air, that is if it's not just the normal sound of the turbo boosting?
 
...
iv always envied those who say they get 60+ perhaps i need economy lessons or A2 driving lessons!
...

A lot of the factors to do with the MPG you receive are to do with your journey - i.e., short journeys to the shops etc really kill the mpg because the engine is still cold throughout the journey. Similarly high cruising speed on the motorway also reduces your MPG significantly (because aero drag is proportional to the square of speed). So the ideal journey for MPG is a long motorway at a relaxed pace.
 
The 90 is loads more thirsty than the 75. Is this normal?

Also the 90 is making a hissing noise when I accelerate. Is this the turbo or air suction? its worrying as the 75 does not do this, is it normal?

No - my experience is that the 75 and 90 have very similar efficiencies.

No - I imagine plugging the car in to a VAG-COM machine should tell of any air leaks and may resolve your first question
 
I'm willing to bet the hissing noise is causing the poor MPG. check the intercooler
 
i have owned 8 75 tdi and got between 60 to 70 mpg . I have owned a 90 tdi for the last 3 years and just managed to get mpg up to 60 mpg but it is shealthed and got 16" tt alloys with 205/50/16 , mpg is better with 15" winter wheels .But i think 90 does a bit less to the gallon but a lot more fun
 
As to your 90 noise is it the viable vane turbo which make a noise when pulling from low revs . All 90s do this all part of the fun of a 90
 
the 75 gives me 620 miles to the full tank (42litres). average of 67mpg. I never take it over 2000 rmp before changing gears, I do a mixture of motorway and city driving, (probably more motorway 60:40 city). The 75 in my opinion is miles better in terms of efficiency. I have the original stats from the Audi order book. You will be amazed to hear that they predicted the 90 to be better than the 75 in economy.


here we go:

1.4tdi sport 90ps urban 50.4 extra-urban 80.7 combined 65.7 mpg

i will try to take a scanned image of the stats from the A2 price list june 2004.

I will check intercooler and hose leaks today. what is a vag-com machine. will most mechanics have one?
 
There's a distinct difference between the usual turbo induction noise and a sucking hissing air noise though, and in my experience, the latter is descriptive of a boost leak - boost leaks are not uncommon on the A2 and they cause all manner of economy and performance issues.

VAGCOM is diagnostic software which you can buy and run off your own computer. However, all mechanics and garages worth their salt will have diagnostic facilities so they can pull the error codes.

Where abouts in London are you? If you're in SW London, I would highly recommend Wak at VAGCheck for any diagnostics and turbo performance repairs -he sorted out mine and my cousin's A2s which both had boost issues last year.
 
Part of the reason the 90 is capable in theory of better MPG is that it actually has a longer 5th gear ratio than the 75.
The 90 responds very nicely to remapping as well, 125BHP is possible, although it can also kick out more torque than the clutch can handle if mapped too far!
Again if you wanted a remap, Wak can do them, or you could pop up to Stealth who seem to be doing more A2 work than anybody else these days!
You can also fit an aerodynamics package which will help a little - it includes front lip spoilers, a front subframe floor spoiler, and an exhaust tunnel cover. All available as a kit from Stoke Audi Parts.
 
Since changing from 17" Sport wheels to 15" pepperpot wheels my fuel consumption has improved by at least 3 MPG overall.
 
Resurrecting this informative thread to see the updated opinion (based on experience and expertise) about 75ps Vs 90ps, DMF Vs SMF
cheers guys
 
No change from me.

My slight preference is still for a well maintained 90 over a 75. But it is only a slight preference.

The renowned Dual Mass Flywheel (on the 90 only), lasts for years once done and costs around £600 or so (including a new clutch) so that is not enough to put me off. The other difference being that the 90 s turbo, being more complicated due to the moving vanes just SEEMS to be a weaker part due to the moving parts, but in reality I still VERY rarely hear of any turbo failures, and even when this happens it is as likely to be a 75 too.

I just like the extra torque and the nice little chirp you seem to get from the turbo and the thought of a remapped 90 is very appealing. (Ask Murdo and others that have one).

Steve B
 
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