1.4tdi Cambelt change - mpg drop...

747tech

Member
Hello all, looking for some pointers here....recently changed cam belt/tensioner and all is ok apart from an increase in fuel consumption of close on 10mpg. (I record fuel use so not just guestimate).

All was ok during belt change re. alignment tools etc. so I'm thinking inj. timing has changed slightly due to incremental difference in belt lengths.

My question is what is needed to check this. I have a bluetooth module which works in diagnostic port but I'm clueless as regards software required etc?

Any help much appreciated.
 
My best assumption is that the crank locking tool has a small manufacturing tolerance fault in it. As you lock the crank, it is a little off TDC, and cam has been locked to this timing.

I expect your cam timing to be retarded, which will result in reduced VE (volumetric efficiency).

I have not had a look at my 1.4TDI yet. I am familiar with VW Passat 90hp and 110hp 1.9TDI Bosch VE-pump engines. 1.9 VW Passat engines have a little window in the tranny bellhousing where to check the TDC (top dead center) on the flywheel.

Basically one can check the cam timing by rotating the engine to it's TDC mark, and trying out does the camshaft locking tool easily glide into it's locking recess. That's all there is to it.

It's an another question whether the factory TDC marking can be trusted. I have always checked whether my engine has the marking in the correct location.
Try google on how to find engine TDC. Keep on searching until you find working description on using stop bolt -method.

Here's my short "how-to" instruction.

On petrol engines this stop bolt tool is inserted into the engine through spark plug hole/threads.
I modified an old glow plug to make similar type of tool. NOTE - make some kinda recess on the tool so it will let out compressed air from the cylinder. This will make engine turning easier (also, remove all other glow plugs while doing this).

Adjust the tool in a manner that upcoming piston will get stopped maybe about 1/4 inch (i.e. 6mm) before TDC. Turn the engine forwards until piston will contact the stop bolt. Make a mark on the flywheel.
Turn the engine other way round (backwards) until piston will stop. Make a mark on the flywheel.

Remove stop tool.

Rotate engine until you can see both of your markings on the flywheel. Exact TDC of your engine is precisely in the middle of these two freshly done markings.

If your markings are too far apart to fit in the inspection window, you have the stop tool inserted too deep into the cylinder. Back up the stop tool a little bit and start over.

If the factory has done a good job, factory TDC marking would need to be precisely in the middle of your two fresh markings.

In case the factory marking noticeably is not in the middle, and is indeed towards either of your fresh marking, the factory has done a poor job in TCD marking and you need to do your own mark down there.

In my old 1.9TDI workshop manual instructed user to turn the engine until TDC marking was visible but kind of "touching" the inspection window edge. TDC marking was a round circle.

After my measurements I noticed that factory tolerances are off by a small margin. I had to adobt a way where I turned the engine far enough that only half of the TDC marking was visible - that's where the true TDC for my engine was.
 
Back
Top