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One to many tweaks?

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Just discovered the technical archives today for the first time! Spent about an hour trawling through a gold mine of info! But the topic that caught my eye was this;


From what I gather it seems like a fairly simple way to improve performance, and the inner boy racer in me is getting excited. So I searched around the forums to find out more and a lot of people who have done the modification are really pleased with the results. But before I start tweaking things I was wondering if there were any drawbacks to adjusting the injector pump, i.e If I were to adjust my injector pump diaphragm 90 degrees clockwise(nb.and not touch any other parts of the injector pump), will it have any negative effects such as engine damage? turbo damage? what are the effects on mpg? Is it worth it? common opinion online seems to suggest so. Has anyone done it and had problems? I hope this is not a labored topic, as always I searched around the forum before asking.



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Adjusting the diaphram by only 90 degrees should be absolutely fine.

make sure you are methodical and mark the position before and after so you can set it back to how it was. When you do it, take it for a drive and make sure there are no clouds of black smoke, a slight haze is fine. Too much smoke can indeed damage things such as exhaust valves, rings, turbos as the egt climbs but that is the extreme case. Also MPG will not be effected noticeably as long as the smoke is kept down.

No problems among anyone I know :)

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It would be very unusual for any engine damage to occur from just turning the diaphragm.

Problems can start after tweaking the max fuel setting. If the fuel is turned up too much, you can start burning valve seats.

If you want to quantify how far you have pushed it, then fit an EGT gauge. IIRC the maximum EGT should be 700 degrees C - but don't quote me on this.

If you adjust the star wheel also, you will probably see an improvement in MPG. Your engine should have considerably more low down torque meaning you don't need to change down so often = better MPG.

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Make small adjustments rather than go whole hog as fuel consumption can suffer badly!

Like 10mpg out of mine not to long ago...

As a start turn diaphram 10degrees star wheel 90 and smoke screw 1.5 turns clock wise

that will be a start.

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i went for the full ish monty,

1.5 on the smoke screw, transforms off boost pick up.

diaphram to full adjustment, approx 180 deg, max fuel as i was upping the boost.

didn't touch the star...no need tbh.didn't want to delve too deep.

and 5-6 turns on the turbo actuator to get more, again approx 1 - 1.1 bar boost.

1500 miles in and i love it!

i always warn up and cool down my vehicles properly so i would hope the head gasket etc willl be ok.

mines an auto so gets less stress than a manual but the differnce is quite noticeable, especially on launch!

stick to the guide, do one bit at a time and keep a note of what you have done.

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The smoke screw it great for pulling away

The star wheel is simple and gives more fuel for less boost as it lessens the pressure required to increase fuel flow.

you need to check the diaphragm though as you could go passed the full fuel point and actually make it worse

it is a concentric cone further the cone is away the more fuel.

also for good performance gains remove or reduce the plastic collar under the diaphragm

although an EGT gauge is really required as it has a steep effect on Temps

but goes very well.

wastegate 3 full turns equates to approx 1psi of extra boost, again go to far and you will most likely do a head gasket.

I ran at 21psi for a good while then settled on 18psi with a calibrated gauge also I have an EGT set up.

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So if you have an EGT sensor, what exactly does that do for you? What would be a good running temperature, and if it goes higher than that what do you do?

I am going to play with my pump today, but only to try to make it less gutless when cold. I don't have an EGT, and don't really want to get too far involved in that side of things. What would anyone recommend as a good change to make for just increasing cold engine pull?


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So if you have an EGT sensor, what exactly does that do for you? What would be a good running temperature, and if it goes higher than that what do you do?

It tells you if you have gone too far with your adjustments. Go too far beyind the reccomended temperatures and you screw up your engine properly so they are really quite useful for doing this. If you have one and the temps do rise too high say prolonged hi throttle on a motorway, you can back off of the throttle to bring the EGT back down again. I cant remember the actual upper limit, but it is something around 700ish degrees, like James says, and you need to start worrying about what you have done.

Having said all of this, i dont have an EGT gauge and i have adjusted my IP, but i would still say an EGT gauge would be useful. I have worked by the theory that as long as there are not huge plumes of black smoke i wont have done too much harm. I have to say that overall, i havent been that impressed by the IP/boost adjustments. Overall, i have an uprated standard size intercooler, boost up to 1bar (currently), on boost fuelling set to max via the cone, the nylon stop ring is removed from the cone rod completely and 1 1/2 clockwise turns oin the starwheel. I'm getting 25mpg no matter how i drive it and this hasnt changed since before the adjustments. Off boost performance is fine, but top speed in terms of holding the 110 at 70 easily with overdrive engaged is still not quite as relaxing as it should be.

The other thing i would mention is to check the IP timing is spot on as well. Mine is just about to get a good service as well, but i do that so regulary, i dont expect that to make a lot of difference.

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OK, that makes sense about the temperature. It's good to know that you have not got an EGT guage fitted though, and I would think that the majority of people who do this doesn't have one fitted either.

When you say to make sure the IP timing is spot on, do you mean doing a cam belt change and/or making sure the pump is not advanced or retarded?

As having your pump advanced is another way to liven up a Tdi, would tweaking your pump when it's advanced cause any ill effects?

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As having your pump advanced is another way to liven up a Tdi, would tweaking your pump when it's advanced cause any ill effects?

This is the first time I've heard this in the realms of car engines. On the engines that I work on (10MW is small for me) advanced timing will induce higher peak combustion temperatures and pressures. This will cause a greater power output, however the shock loading on the engine components is increased hugely. Think of it as smacking piston/conrod/crank/bearings with a 25lb sledge hammer rather than a 5lb lump hammer under normal operating conditions. Normally you can tell if an engine is too far advanced as it will knock horribly.

If you are running on a fuel with a lower cetane value (veg oil mostly), advancing the pump can be a good idea due to the lower flame velocity in the cylinder.

So, I wouldn't advance the timing beyond standard. But then I wouldn't trust the timing marks anyway and would end up setting the timing by ear anyhow. :rolleyes:

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