2.5 TDi cold starting

[oh_superb]

I have posted on this before by hijacking another similar thread, so here we go again.

Cold starts are lumpy and shaky, it's as if it misfires on 1-2 cylinders.

Resistance of glow plugs was checked, all identical, around 0.8 Ohm cold.

Voltage feed to all the glow plugs was checked when the glow plug relay was on.

Last few mornings the cold starts were worse, so not just say 1-2 s worth of shaky smokey TDI lump, but worse, 5-8 s required to stabilise idle, and to fire on all.  That is enough to induce sufficient diesel smell in the street to start being the tea time discussion subject of my neighbours :-))

This morning I also heard like tappety/diesely/knocky combustion coming in and out, a bit like when I had the injection pump failure 13k miles ago :-(((  But much less severe of course.  Like the advance servo was hunting a bit.

I started thinking.  And got more and more concerned...

Then I decided to pop the bonnet and have a good look.  Spotted a bubble in the clear diesel line.  After parking the car for 20 min after another 170 mile round trip I decided to open the bonnet and have a good look at the "bubble".

OK, now, on a restart, as the engine picks up (faultlessly when warm/warmish) I spotted around 5 "glugs" of air in the fuel line within the first 3-4 seconds of idle, and then was clear, they were sucked through the injection pump and gone.

So, if that much air is dragged in in only 20 minutes, how much could there be sucked in overnight??  Yet to be checked on the next cold start….

Could this be giving me cold start problems, i.e. air in the system and effectively I might also be giving the IP a hard time as it has to pull all that air through every morning?

Where could the air be coming from?

One of the fuel lines attached to the thermostat valve on the fuel filter seems to be perished a bit.

I also read somewhere that the gasket underneath it could be leaking air in also.

What about the injector spill lines? The whole area around there is damp, not sure if engine oil or diesel or a combination of the two.

 

Where shall I start??? 

Edited 16 January, 2015 by oh_superb

[dieselV6]

Check fuel lines in engine bay, fuel filter - has it been replaced recently? Could be that the fuel filter has been there for a while and got partly stuffed with wax now that winter is here. "air" in lines that you see could be vacuum/vapour.

 

The o-ring on fuel filter tee is another point to check, although usually I get fuel on the filter if the "tee" is not properly seated.

 

Next would be fuel pickup in the cabin, behind rear seats, undo the cover and see if connections are OK.

If you do not find anything in engine bay nor at fuel tank, underbody inspection might be in order, I have RRP so fuel lines covered, but I'd imagine it's possible to snag them.

 

But I'd start with installing a new fuel filter and checking if the problem goes away.

[oh_superb]

When I had the fuel pump overhaul (at 121k, now 133k) the garage said they would change the fuel filter.  Not sure they did, nothing of such was on the receipt and if they didn't then the filter is 30k miles old (I have just checked the records) having last been changed at 103k.

Even if they had changed it, it would now be 12k miles old.  But I suspect they didn't.

 

Do you mean electrical connections under the cover?  I do not remember seeing any fuel lines there, but it's been a while since I last poked my head in there.

[dieselV6]

There are fuel line quick-connect couplers on top of fuel pickup behind the rear seats. But as I had stated already, I'd replace the fuel filter in the engine bay first and see if the bubbles disappear. BTW, if they do, there is a certain probability that the partial fuel filter blockage killed your last IP (if fuel filter was not replaced around IP replacement).

[oh_superb]

At the time of the last IP replacement the fuel filter was 17k miles old and the connection had not been disturbed for months prior to the IP failure/replacement.

OK, I'll get a new fuel filter installed.  Is advice for OEM?  Or Champion?

 

ECP are out of MANN ones otherwise I'd get that, though I'll ring the local ECP shop and see if they may stock one.

[dieselV6]

I have used Mann, Bosch, Mahle and VAG in the past, the important thing to check nowadays is that the "T" o-ring is intact, I had recently a Mahle which was leaking due to pinched o-ring, otherwise very good.

Best to moisten the o-ring with fuel before replacing the "T". As I have said, it is a starting point, at least in this way you make sure the air leak (or vacuum due to blockage) is not related to the fuel filter.

 

The fact that engine works better/unchanged after a while supports the theory of fuel filter partially blocked, as waxes tend to melt when fuel heats up and fuel flow through the filter improves.

 

I only now noticed the comment on spill lines, they go back to the tee. I'd clean up the area under them with brake cleaner first, and then try to smell the difference :p  after the next engine start.

But when engine is running, these lines are under positive fuel pressure, as most fuel from IP goes into them (injectors only take a fraction of the feed, depending on power demand).

Edited 16 January, 2015 by dieselV6

[jimbof]

So do you 2.5'ers only get one O-ring on the thermostatic tee?  I knew there was a reason the 1.9 was superior...!  We get a pair of crazy colour coded rings

[oh_superb]

I lent my vacuum oil extractor to a friend this weekend… previously I used it to suck fuel through.  Is it too risky to approach the fuel filter change without the vacuum TP69?  What I meant was pinch the feed from tank and pinch the feed to IP and fill the new fuel filter with fresh diesel, and pray?

Or foolish?

Don't want to have to revert to the Jazz for the rest of the weekend :(((

[dieselV6]

I guess if you fill the filter fully with diesel, you should be OK. Suction pump gives a guarantee of instant start afterwards, you might need to crank it. You might need to wait a while afterwards for air to exit the fuel system.

[oh_superb]

Decided not to gamble, so bought a genuine diesel filter and had it fitted at a garage.  All inc cost 48 pounds, I'll see what happens in terms of cold starts, but it was due anyway.

If still lumpy will see what to do.

However, something that is obvious now that I had my first cold start since brimming the tank with Shell fuel is that it is not as lumpy on Shell as it was on supermarket branded fuel.  Either different waxing characteristics, or the glow plugs are not that hot any more and there is an increased sensitivity to cetane.

But I did check the fuel line this morning on the cold start at 0 deg C and no air was getting pulled through (contrast to warm start observed yesterday where I could see bubbles).

[Gaz]

So do you 2.5'ers only get one O-ring on the thermostatic tee?  I knew there was a reason the 1.9 was superior...!  We get a pair of crazy colour coded rings

 

Quality over quantity Jim, quality over quantity.

 

Gaz

[iob]

Funny thing, although I have changed 4 out of 6 GPs, after filling the tank with winter super diesel, I got smoother cold starts... Maybe the GPs are not the main or were not the sole culprit for the shaky cold starts?

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Edited 17 January, 2015 by iob

[oh_superb]

I was going to try Shell Super diesel, but the pump where I stopped to fill up had none.  

So less shaky on Shell than supermarket.

Now I have a new filter too, so I shall see tomorrow if any further improvements...

Ageing glow plugs is the other option… they are all 58000 miles old (5 years).

[iob]

In my case, the GPs were the original ones, 7 years old (130 k km)...

I retrofitted the pump's hydraulics some 40 k km ago and not had any issues since. I do remember that before it failed, the tell-tale signs (shakes and hiccups), were happening at idle as well as under load, as opposed to now. At least I hope I can rule out the IP as cause for the rough cold starts, since except for the first 3-4 seconds, running is smooth. I will also follow up on the last tank fill and see if the improvement will last. Otherwise, it's back to the drawing board...

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[oh_superb]

OK, so cold start this morning, exactly the same as yesterday, shaky, smoke, for 5 seconds.  Therefore, the new fuel filter did not improve it.

I still have the temptation to replace the glow plugs.

But tempting to unplug a glow plug a day and see when the start does not get worse.  That would point me to the cylinder(s) with the issue and it would take me a week to identify which ones still work and which ones don't.

Then target the specific glow plugs.

Or just replace the lot.  It's just that I am not convinced it would get better, all had exactly the same resistance and they are not that old.

And I read on an Audi forum that another owner had similar symptoms and they did not improve with new GPs.

I'm dreading worn cams on the left bank :-((((  The lobe through the oil filler cap seems OK though.  The right hand cylinder head is definitely OK, as I it's the fresh one installed at 74000 miles when the glow plugs snapped, and I had a good look when I changed the needle lift injector a year ago and all was immaculate.

Is the tank pump supposed to kick in during cranking or just when the idle picks up?  What if the injection pump gets into cavitation due to not enough feed pressure?

[iob]

As far as I know (please don't stone me if I'm wrong [emoji15]), the 2,5 tdi doesn't have a lift/tank pump... But could still be an issue of air in the system from several points along the way.

Mine started smooth this morning (no shakes, maybe a slight idle cough for 1-2 secs), but on the other hand today was not as cold as usual (4 deg C), so I'm waiting for some minus to see if the diesel made any difference...

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[oh_superb]

Not sure about tank pump any more.  Read somewhere that as far as A6 is concerned only the Quattro version had a lift pump, so perhaps you are right as there are no 4wd Superbs.

I have also tried Millers EcoMax. It gave me an extra 2mpg at any given speed. But cold start was unchanged.

I have some more ideas, will keep you posted.

[dieselV6]

AYM might have lift pump, BDG has just large fuel pickup.

[iob]

@oh_superb: Speaking about additives, I am using the 2 stroke oil mix in 1:250 ratio, as recommended (off the record) by the Bosch pump specialist, after fixing my VP44 hydraulics which failed due to the low lubricity of the Euro5 diesel fuel; but this has nothing to do with these symptoms, as the ratio is low and this would the 3rd winter using it and first time with the symptoms;

On other forums I read that changing the o-rings of the "Tee" valve on top of the fuel filter might help against false air intake... I might check that as well and keep you posted on the progress.

@dV6: my engine is the BDG, but I thought all the 2,5 with VP44 are without the lift pump...as I said, not sure about it, just that mine doesn't have it.

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[oh_superb]

@oh_superb: Speaking about additives, I am using the 2 stroke oil mix in 1:250 ratio, as recommended (off the record) by the Bosch pump specialist, after fixing my VP44 hydraulics which failed due to the low lubricity of the Euro5 diesel fuel; but this has nothing to do with these symptoms, as the ratio is low and this would the 3rd winter using it and first time with the symptoms;

On other forums I read that changing the o-rings of the "Tee" valve on top of the fuel filter might help against false air intake... I might check that as well and keep you posted on the progress.

@dV6: my engine is the BDG, but I thought all the 2,5 with VP44 are without the lift pump...as I said, not sure about it, just that mine doesn't have it.

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Hi mate.

I was contemplating starting the 2T oil treatment too… there is evidence that they help keep the injectors clean and make pump last longer.  It is not cheap though over time, and one had to remember to carry it around...

I am also thinking of changing the nozzles on my injectors.  I have previously read somewhere that at this mileage the spray pattern is likely to be all over the place, which won't help performance or cold start behaviour.  Do you know the standard hole size?  I keep finding 0.216 nozzles, but have a gut feeling these are oversized, which is not necessarily a problem but the idle would need to be re-calibrated I think for the reduced pulse width.  I don't know if it is worth going to a Bosch specialist to check other injector parameters, like crack off pressure and flow rate etc, not sure if this is required when you re-build an injector DIY to save cash.  Local bosch agent quoted GBP12 to check an injector and if it requires a rebuild around GBP 70 each.  So with 6 of them (well one is a year old so could skip that one) it soon adds up to some cash, so if I could do it myself for half price or less, then I would.  Otherwise I don't think I will bother on an old car.

I had a new genuine VAG filter installed two days ago, and presumably they would have changed the O ring on the Tee, all filters come with this O ring (I did not open the package but previously Mann supply it and I am sure VAG will also.

One problem I had before was that the O ring was not seated properly, it had a fold on one side (again I paid someone to install it incorrectly - sad face) and the car was drawing in air overnight and would not start in the morning.

Main reason I was putting off installing a new filter was that every single time there was some sort of a scene/problem with it.  I must say it is the most idiotic design, compared to all the previous diesel cars I have owned - Nissans, Peugeots, Citroens… not a single time did I have a problem replacing the fuel filter and re-priming the system.  But on these cars…. ahem.

My next port of call is checking the regulating valve on the IP in case it is stuck open the giving too low a casing pressure inside the VP44.  Timing regulation would be affected which sort of shows my symptoms - possibly.

I just need to pull off the top branch of the inlet manifold for access.  Now where's that tool box again? 

Edited 19 January, 2015 by oh_superb

[iob]

Hi,

 

Re 2T oil treatment, I am using the Mobil Extra 2T since almost 3 years and 40 k km as a preemptive measure recommended by the Bosch specialist and read few materials which praised it...I wouldn't say it's too expensive, since I can get 1 bottle of 1L for ~ 4 quid and will last for ~ 4 fill-ups (roughly 2 quid/month for my peace of mind is not that much)...The drawback is to remember to pour it in at every fill, especially if you are in a hurry - carrying it around is simple, I always have 2 bottles stowed in the trunk  

Re nozzles, sorry m8, I have no idea on the size as I didn't research the subject, apart from hearing about fitting oversized ones as part of higher stage tuning projects... I understand the logic behind the spray pattern over time, but wouldn't be on the safe side to stay with the original size, in order to avoid further complications? Depending on how much longer you would like to keep the car, it might worth at least checking them by the Bosch specialist.

Re filters, the last 2 I changed were Mahle, previously I have used only Mann, but for whatever reason I cannot find it anymore on the local market. I don't think that there is any difference in quality between the 2, but I don't like coincidences so I think I will change the fuel filter soon as well with either VAG or Mann if I can find one...

Good luck with your endeavours and please do report on your findings, I will do the same...

Cheers,

[oh_superb]

Ok mate will consider 2T oil for the future feeding of the beast.

Today I borrowed a Fluke 365 current clamp meter from work and checked the glow plugs.

The total draw is maxing out at 120A then settles to around 50A.

Individually tested they all draw a peak of 20A.

So that seems OK.

However, on first key on the total draw time today after 5 hours of siting outside in 1-2 deg C above freezing is 3 seconds before the feed dies.

Then on next key on it is 6 seconds! Double the first one!

Incidentally this morning I tried double cycling the glow plugs and the quality of the start was much improved.

I wonder if I have a problem with the relay or ECU or something else. I do not understand why the glow time would change from 3s to 6a unless the heat that's already in the glow plugs is affecting the resistance and hence something else. But the peak current was still the same in both cycles around 110-120A. The screen refresh was only about 2Hz so I cannot be 100% on exact peak. But I videoed the whole spectacle and kept watching it for entertainment purposes as it's quite interesting.

If I do renozzle my preference would be stock.

Edited 19 January, 2015 by oh_superb

[dieselV6]

Glow plug time sounds a bit on the short side, mine took about 5s for the GP light to go out and likely double that in total glow time, at ~3deg C. Could it be a dodgy GP relay or one of temperature sensors is faulty? (Coolant, fuel, ambient air, IAT and so on) Perhaps it would be good to check various temp values with VCDS on a cold engine to see if the readings are plausible. If double cycling GPs improves the start markedly, and the glow time looks short, fuelling issues are unlikely IMHO (unless fuelling would also be related eg to faulty temp sensor reading).

[iob]

A commonly reported cause for the inconsistent glow time (also related to outside temperature) is the failure of the G62 coolant temperature sensor. If you have a VCDS, you can check the difference between the temperature shown in the instrument cluster and the one in measuring blocks. Higher than 5 deg C difference means the sensor should be changed, lots of people had this issue on our local VW forums...

 

@dV6 - Just when I was about to post the above, yours just popped up   

[oh_superb]

Yes, guys, I was thinking along those lines too…  VCDS laptop tomorrow morning then :-)

This evening I left work around 7 and it was -1 outside, the car having sat still all day, and again first GP cycle around 3s, the second around 6s, and fired up pretty much OK, not dead smooth, but absolutely fine.

The CTS is a year old.  I had issues with them before, some sent the wrong signal to dash, but OK to the ECU, some the other way around.  In fact the last one I had was giving me cold start problems, easily diagnosed in VCDS with temp discrepancy between ambient and displayed.

I then fitted a Topran made one and has been OK.

Will check in the morning.

 

The other thing I was going to say is that I can hear clicking after a cold start while the engine is idling/car moving/whatever for around a minute, I reckon around 1 Hz.

Is the the GP relay cycling to maintain glow without burning them, in the absence of PWM control of some later vehicles?

Just wondered if anyone else has been hearing this.  It comes from the fish box area, I guess the relays are there too, including the GP relay?

Edited 19 January, 2015 by oh_superb