Passat 2.0tdi dsg 170 starting problems from cold

[scanny1]

Can anyone help,I have a Passat. 07 2.0tdi dsg sport 170 and when the car is left over night it hesitates to starts and engine sometimes judders when it starts up,the car drives as it should and would start up ok throughout the day ,I've had the battery replaced as the old one was no good ,also the glowplugs replaced as 2 were no good ,also the Intank fuel pump replaced because the pump had packed in ,and the tandem pump was changed because the it was mixing oil with deisel and finally fuel filter ,I've taken the car to a vw specialist even they can't put there finger on the fault they linked it up with the vag software and they said everything seems fine ,so any ideas please

[DMitch16]

Dirty or partially blocked injector.
Injector lash adjustment incorrect.
Sticky or untrue valve.
Timing adjustment needed (there is scope to alter the timing to ease hard cold starts).
Dual Mass Flywheel worn, partially seized or failing - DSG boxes are harder on DMFs than manual gearboxes.

A few things for thought

Scans for fault codes just reveal that and that only.

What you want is for the VW specialist to monitor certain measuring blocks in the ECU to see what the engine is doing upon cold start, how it runs thereafter, to monitor fuel delivery, fuel trim quantities (highlights bad or inefficient injectors) and check things like the fuel tank pump voltages / resistances. If they are truly a VW Specialist they should know this already.

The rest is basic mechanical knowledge and experience of engines in general. After all no matter what you bolt to it there's always a block, crank, cylinders, pistons, head, valves, carbs / injectors, camshafts and they have all worked pretty much in the same way give or take for donkeys (unless you have a good Wankel of course!).

[scanny1]

The car doesn't misfire so I didn't think it was anything to do with the injectors ?also what do you mean lash adjustment on the injectors ,the gearbox seems fine no vibrations to say the flywheel has gone ,When I took the car he did all the checks you said and told me all within tolerances

[DMitch16]

It doesn't have to misfire to still have a partially blocked injector (I am referring to the delivery holes in the nozzle which spray the diesel in an atomised pattern). If one or two holes are blocked the diesel delivery is reduced and the optimum spray pattern disrupted. The idle becomes lumpy, more so if more than one injector is fouled in the same way but bear in mind these engines have a reputation for lumpy idling.

Injector lash is the gap by which you back off the injector strike from full stop (piston plunger bottoms out inside injector). The adjustment is 180° before full injector piston plunger stop at the lowest point of the injector strike cycle. This is an involved procedure, involves removing the cam cover (fit new gasket) and is not for novices. Setting this correctly reduces noise and should make for a smoother idle.

You don't always get vibration when a DMF starts to fail and when I mean fail the two plates that are bonded together start to move excessively against the internal springs and therefore may cause harder starts but still function in a seemingly normal way. Eventually noise would be heard as the plates of the DMF loosen further with the excess travel creating movement not only rotationally but also laterally.

Other reasons for harder starts are a stiff starter motor, excess fuel or oil in cylinders (leaking seals or injectors overnight) and car resting against the Park setting - always stop the car with the foot brake, select neutral, apply the parking brake, release the foot brake so the car fully rests on the parking brake only and THEN engage Park with the gear selector lever. This also helps to preserve the condition of the DMF and gearbox as starting a car resting on the Parking gate puts harsh forces on connected parts.

These are only suggestions based on my own experiences and there may be other reasons why you are experiencing hard starts and shuddering on cold starts.

[scanny1]

Cheers I'll try that first by pressing hand brake then placing it in park ,but with the injector spray pattern would that of been picked up on a vag scan or vcds scan but to be fair the car runs mint can't fault it that's why I didn't think it was the injector as I've had that before on an old hdi where the injector was partially blocked and it ran like it was on 3 cylinders .im trying a method of clamping the supply fuel hose from the filter to the tandem pump in case its air that's being purged out when I'm trying to start it up ,so tomorrow morning I'll unclamp it and see what happens ,if it's ok maybe a double check valve

[DMitch16]

You do sometimes get a seepage / cross contamination under the tandem pump due to the less than perfect gasket between the head and the tandem pump especially if the bottom bolt is not tightened correctly or abrasives used to clean the respective faces which should be clean and dry before fitting the gasket. Often people mistake the fuel in oil / oil in fuel cross contamination as an internal fault in the tandem pump but in reality 6 out of 10 cases are the gasket gives and the fuel and oil gets pushed into the wrong holes in the head. There is an internal seal kit to repair the tandem pump saving over £150 if it does fail internally.

Group 013 of the engine measuring blocks gives the idle fuel trim figures with tolerances between 1 and -1 ok but better the closer to 0.00 you get. Your specialist should be able to review these and any injector out of this range may not be working efficiently or is leaking. Since changing my seals and tandem pump gasket mine run at an average of -0.42; +0.20; -0.03 and +0.47 which is very good for the age of the injectors / engine. Before they were all over 1.00 / -1.00.

[scanny1]

I changed the tandem pump and I did recall tightening issue with the bottom bolt on the pump can't remember weather it was awkward to get to ,so might be worth looking at that again ,do you think I could buy the gasket between the head and the pump if needed thanks

[DMitch16]

It's awkward - there is a coolant pipe flange connected to the head at exactly the point you'd want straight access to the bolt. I use a ball end Allen key and a ring spanner (locked onto the short part of the Allen key for leverage). The important thing is to get the surfaces clean and as dry as possible - a bit more difficult when there's oil and diesel traces seeping out of the holes in the head. I use a cloth (not paper towel) soaked in brake cleaner as it evaporates quickly. Wipe the two faces, apply the gasket to the pump face, quickly engage the pump (having pre-aligned the drive pegs with the cam slot) and bolt evenly to the head pinch tight then tighten the bottom bolt further (almost impossible to torque this one so I have to gauge when it is tight enough - pretty tight is my setting as you can't really get too much purchase on the Allen key ball due to the angle). Then torque the upper bolts to 23Nm (3Nm above requirement which seems to do the trick and holds it tightly).

New gasket is available online for sub £15 or around £20, more or less, from the dealer. Reject any that have been squeezed into a plastic bag as the parts idiots keep doing this which renders them bent and therefore unusable.

[scanny1]

I released the clamp from the fuel pipe this morning but the car just started up the same as before .if that gasket had gone again would there be oil in the diesel ? I've checked the oil level and its not increased incase diesel was leaking in

[scanny1]

The gasket I meant the tandem gasket .
ive read threads saying it could be a cracked head but there's no loss of oil or water and the performance is faultless surely a good specialist would sort this out been like it a year now