Timing the TDI

This applies to 2.5 TDI models, 88, 102 and 151 hp models 1996 - 2003.

This is not a how to, this is not a blow by blow account, just a page of notes on some pitfalls that you are likely to encounter.

Chances are your garage will do this work for you, after reading this you should have a pretty good idea of what is involved and what to quiz your garage about to gain confidence in them, and, more to the point for you, the owner/driver to feel like you know whats involved so it feels like your getting your monies worth when you get your bill!

The engine is TDI, Turbo Direct Injection. This IS NOT for 2.4D

To achieve lower exhaust emissions, good economy and good power output these engines are completely computer controlled.
There is no throttle cable (known as fly or drive by wire) and the Diesel injection pump is controlled by an electronic governor. This system is designed by Bosch and carries the Bosch trade mark name of EDC, or Electronic Diesel Control.

The electronic governor is an output of the ECU (Engine Control Unit, basically a computer) and it's output is determined from several inputs into the ECU including throttle position, air flow into the engine, engine temp, ambient air temp, boost pressure and temp etc...
Basically there are loads of sensors to get the Diesel pump to make the best of what is available using the parameters supplied.

Obviously, this precise computer control requires an above average level of service when it comes to cam belt change or pump replacement.

The service interval for the cam belt (timing belt) is 80 000 miles. Although it is prudent to change them early as if they do fail chances are it will destroy the top end of the engine and you risk piston damage.
Please also take into account that it is often not the fault of the belt itself when failure occurs, water pumps, belt tensioners and idler pulleys can all kill an engine.

When replacing the timing belt it is recommended that you change both timing belts (the injection pump has it's own drive belt, separate to the main cam belt) all the tensioners, the idler pulleys, the water pump and the crank shaft pulley bolt as well as the rocker cover gasket.
You will also need some coolant as when the water pump is removed you will loose some and chances are it will be contaminated when it runs off the engine block.

Shopping list.

  • Timing belt.
  • Injection pump belt.
  • Crank shaft pulley bolt.
  • Water pump.
  • Rocker cover gasket.
  • Timing belt tensioner.
  • Timing belt idler pulley.
  • Injection pump belt tensioner.
  • Injection pump belt idler pulley.
  • Coolant (G12+)
  • Auxiliary drive belt (fan belt to you and me)

That lot above will set you back around £200 from a VW main dealer.

The timing belt.

As per just about every other VW Diesel, the cam pulley is wedge mated, it is infinitely adjustable.
You really need to set the engine to number 1 TDC before starting work.
This end is fairly much nuts and bolts, TDC is found marked on the flywheel, it's a bit of a swine to see but it is there, there is an inspection hatch (rubber bung) on top of the bell housing, with a pointer that, er, points to a mark on the flywheel.
Rocker cover off.
Okay, now on the injection pump is a 10mm bolt, near the pulley end of the pump, it has a little fork shaped wedge/plate thats it holds in.
If you slacken this bolt, remove the plate and keep it safe, nip the bolt up, this will hold the injection pump in the right sort of position.
Remove injection pump pulley cam sprocket bolt  and fit the timing bar to the back of the cam.
Change the cam belt in the time honoured fashion.
Rattle the cam belt back together.
Ignore the injection pump end for the minute and make sure you ain't cocked up by turning the engine over twice to make sure nowt touches.
Once you are satisfied all is well at the timing belt end, switch you attentions to the pump belt end.
make sure the engine is bang on, 100% on TDC #1

Okay, there are a few ways of setting this up.

On the pump pulley, should be a mark that corresponds with a mark on the pump body, or bracket, thats number one, make sure it is.

Fit your belt, tensioner and idlers.

Nip up the cam sprocket.
Undo the 10mm lock nut on the pump, slide the plate back in.

**Never, ever turn the engine with the belt connected with the wedge/plate removed from the pump, you will break very expensive... er... things)**


You should be somewhere near now, and it will probably run but...

The injection pump needs to be set into such a position so that one of the actuators in the injection pump has enough leeway to adjust the timing backwards and forwards to achieve economy, smooth running, low emissions and power. This means a "basic  setting" has to be carried out.

The old school way.

If you have messed around with VW Diesels before chances are that you will be familiar with a DTI (Dial Test Indicator)
This precise piece of equipment measures linear movement down to 0.01 of a mm.

You fit the DTI to the back of the injection pump through the timing port via a threaded adaptor that fits between the injector pipes in the pump head.

  • Pre load the DTI
  • Wind the engine backwards till the DTI needle stops moving.
  • Zero the gauge.
  • Wind the engine back up to TDC.
  • measure the reading on the DTI
  • The measurement you are expecting (or aiming for) is .55mm

If the measurement in more than .55mm the timing is too far advanced.

If the measurement is less than .55mm the timing is retarded.

To adjust the timing you do the following.

  • Slacken the pump lock bolt via the 10mm headed bolt, remove wedge and nip up.
  • Slacken injection pump timing belt at the cam pulley.
  • Hold spanner on the injection pump sprocket pulley and slowly undo the pump lock.
  • Set the DTI to desired position.
  • lock pump by tightening the bolt.
  • Tighten cam pulley.
  • undo pump lock and refit wedge.
  • Recheck timing.

Once you are happy that the basic position is set, make sure all pulleys are tight, and the pump lock set to unlocked.

Test engine.

Now this works, to a degree, this figure [.55mm] was set on a new engine, but using this method I have found that the pump has had to be set as far as .7mm lift @TDC to achieve what I am meant to when diagnostic equipment is used.

A few ways of checking with diagnostic equipment.


VagCom timing checker.

If you have VagCom, there is a plug in (supplied with latest versions of the software)

  • Connect VagCom.
  • Go to engine.
  • Go to "Measuring block"
  • Select "Switch to basic settings"
  • press the " TDI Timing checker"
  • You will now get a pop up window with the timing checker app.
  • Select your chassis and engine from the drop down menu.
  • The timing will be displayed on the chart, or as digits towards the bottom of the page.
  • You are aiming to achieve "55"

Just reading off what VagCom says.

  • Connect VagCom
  • Engine
  • Measuring block.
  • Switch to basic settings
  • Group 0

You will now get a list of numbers, in the second box should be 55, or there abouts, thats your pump timing.

If it's not, over 55 is advanced, below 55 is retarded.

The proper VW way.

  • Connect Vag Com
  • Engine
  • Measuring block
  • Switch to basic settings
  • Again, a list of boxes with numbers.
    Write down boxes 2 and 9.
  • Now, in the factory repair manual there is a chart, you plot the figures you gleaned from VagCom onto the chart to see if the timing you have is within factory limits.


Another way

  • Vag Com
  • Engine
  • Measuring block
  • scroll one of the lines to group 004

This shows.

  1. Requested ignition timing
  2. Actual ignition timing
  3. Duty cycle

Now, I need to check these parameters but, from what I have read..

If the actual timing is between .5° and 2° and the duty cycle on or below 10%, everything is cool.
Duty cycle over 10% then the ECU is doing too much to correct what is going on and timing adjustment are to be made.

I will update this method when I can find out a bit more about it.

Adjusting the timing.

It's properly hard to get it bang on, it takes a fine hand and a bit of practise, again, make adjustments by tiny movements on the cam pulley for the injection pump.

You can either undo the bolt and move the pulley in relation to the cam to get it near or use the idler pulley and the tensioner pulley for smaller adjustments.
By this I mean, use more tension on the lower idler, then back off the tensioner to make sure the pointers are in line, or vise versa, tighten the tensioner then back off the idler to retard the timing.

It is imperative that the pointers on the injection pump belt tensioner are EXACTLY in line, or things are going to go really, really wrong for you, mind you, the same can be said for the cam belt tensioner too!

Link to VagCom from Ross Tech

Other pages worth a visit.


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