VAG PD owners: some experiences with the "resistor mod"
20 April 2006, 03:28 PM
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VAG PD owners: some experiences with the "resistor mod"
As I'm possibly the last VAG PD diesel owner in the UK to try one of the 'resistor mod' tuning boxes I thought I'd report on my initial findings over the last 600 miles or so.
Car is a 2002 model Passat PD130 sport, bog standard apart from an £18 tuning box on the fuel temperature sender, bought from a German supplier. I don't know what value resistor is in the box. Car has 42,000 miles up, owned from brand new.
On fitting, extra torque was immediately noticeable from 1500rpm upward.
Tickover is a tiny bit lumpier when engine is hot but certainly not a problem, and most of the time not really noticeable. Cold tickover and starting is no different to standard.
Throttle response is more abrupt than normal, a little finesse is required to stop lurching when going on and off the throttle but you soon get used to it.
There is no more smoke / soot than normal (as observed by my dad, following me for 20-odd miles ... although mine has never been sooty anyway).
No check engine light or fault codes after 600+ miles of mixed driving, including sustained high speeds and long periods in traffic jams (the pre-2003 PDs are supposed to be better than post-2003 for not giving fault codes with this mod, apparently).
Figures:
On my private test track, 40-60mph acceleration in 4th gear is a repeatable 7% quicker (now 4.6 seconds average, compared with just under 5.0 seconds average without the box). Other in-gear times show a similar 6-7% improvement.
Actual brim-to-brim fuel consumption has increased by about 3-4% (down from my usual 46-47mpg to 44.5) over the same type of driving.
The fuel computer is waaaaaayyyyyy off -- it's now about 25% optimistic overall, where before it was just 5% optimistic. However, it's more optimistic at light throttle / low load than it is at motorway speeds.
Overall -- a good bit of fun for pocket money costs
Car is a 2002 model Passat PD130 sport, bog standard apart from an £18 tuning box on the fuel temperature sender, bought from a German supplier. I don't know what value resistor is in the box. Car has 42,000 miles up, owned from brand new.
On fitting, extra torque was immediately noticeable from 1500rpm upward.
Tickover is a tiny bit lumpier when engine is hot but certainly not a problem, and most of the time not really noticeable. Cold tickover and starting is no different to standard.
Throttle response is more abrupt than normal, a little finesse is required to stop lurching when going on and off the throttle but you soon get used to it.
There is no more smoke / soot than normal (as observed by my dad, following me for 20-odd miles ... although mine has never been sooty anyway).
No check engine light or fault codes after 600+ miles of mixed driving, including sustained high speeds and long periods in traffic jams (the pre-2003 PDs are supposed to be better than post-2003 for not giving fault codes with this mod, apparently).
Figures:
On my private test track, 40-60mph acceleration in 4th gear is a repeatable 7% quicker (now 4.6 seconds average, compared with just under 5.0 seconds average without the box). Other in-gear times show a similar 6-7% improvement.
Actual brim-to-brim fuel consumption has increased by about 3-4% (down from my usual 46-47mpg to 44.5) over the same type of driving.
The fuel computer is waaaaaayyyyyy off -- it's now about 25% optimistic overall, where before it was just 5% optimistic. However, it's more optimistic at light throttle / low load than it is at motorway speeds.
Overall -- a good bit of fun for pocket money costs
20 April 2006, 03:35 PM
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Originally Posted by brickboy
No check engine light or fault codes after 600+ miles of mixed driving, including sustained high speeds and long periods in traffic jams (the pre-2003 PDs are supposed to be better than post-2003 for not giving fault codes with this mod, apparently).
Resetting the fault light requires a trip to the dealers or someone with VAG-COM.
Owners with cars in warranty need to be very carefull.
Cheers
Lee
20 April 2006, 03:44 PM
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@Joey: it's like one of these http://cgi.ebay.co.uk/Diesel-Tuning-...QQcmdZViewItem
Essentially, the VAG PD motors make the diesel fuel hot (sometimes up to 90C) because of the high injection pressures. As diesel gets hotter, it gets less dense, which means less energy can be got from a given volume of fuel.
The PD engines have a fuel temp sensor. The tuning box plugs into this and has a resistor in it. The resistor reading fools the ECU into thinking the diesel is hot. The ECU compensates by extending the duration of injection = more fuel per cycle = a bit more grunt.
Lee is absolutely right, it's reckoned that the ECU maps changed in 2003 making them more sensitive to this mod. Pre 2003 cars don't seem to have a problem.
Essentially, the VAG PD motors make the diesel fuel hot (sometimes up to 90C) because of the high injection pressures. As diesel gets hotter, it gets less dense, which means less energy can be got from a given volume of fuel.
The PD engines have a fuel temp sensor. The tuning box plugs into this and has a resistor in it. The resistor reading fools the ECU into thinking the diesel is hot. The ECU compensates by extending the duration of injection = more fuel per cycle = a bit more grunt.
Lee is absolutely right, it's reckoned that the ECU maps changed in 2003 making them more sensitive to this mod. Pre 2003 cars don't seem to have a problem.
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