Undriveable when cold

Can't find this problem listed in earlier posts. 2014 Passat with 75000 mi runs well, 41+ mpg overall. My problem is that the car is essentially undriveable for the first 1-2 miles when cold, ie, less than 30 F. The colder it gets (Minnesota cold), the worse the misfiring/slapping noise/stumbling. Dealer changed air and fuel filters and tested injectors, which were within spec but not ideal. They checked with VW and guessed replacing injectors might help ($1700 parts/labor), which I declined. Aside from extending warmup time before driving, is there a way to fix this without spending a fortune? I could sell it back to VW but wife and I both like the car.

a 2014 should have the latest software, its common for them to buck and fall on there face between 0 and 35mph as the ECU fires the #4 injector on the exhaust stroke sending 1,200F heat threw the DPF to get it up to EPA regulations as quick as possible. If its truly undividable and not just annoying yours may have a sticky exhaust throttle, this unit creates back pressure as needed, but if stuck will be a huge problem- its located about midway on the system and has a unmistakable electric motor attached, you can take it apart and clean the carbon and rust out of it for free. Do a search on here, many in salt belt have had to do this.
https://forums.tdiclub.com/showthread.php?t=431512

Modern high-tech diesels can not completely compensate for cold temps with perfect driveabilty. My engine makes some light 'nailing' noises on cold starts (25F or less). The noise and lack of driveability is a combination of improper combustion from a cold combustion chamber mixed with injectors that are way past new, but not worn out. Some things that reduce the noise and improve cold start drivability:

After starting the car wait at a bit (~30 seconds) before taking off. If you have more time to wait, then wait. A few minutes really helps a lot. You are already doing this. In a cold start case, patience is a virtue.

Add an all-in-one winter fuel additive (cetane boost, anti-gel, lubricity additive, and solvent). Cetane boost helps a lot for those cold starts. Winter fuel is blended for cold flow (more kerosene content), not for increased cetane which really helps cold weather starts. Use whatever brand is on sale. I pour in a lot, as much as 3x or 4x of the recommended dose. Typical 1 quart/liter bottle usually treats 100 gallons, so yes, I'm almost pouring in the whole bottle. I'm overdosing the fuel but all I'm doing is wasting some money for the cause of maximizing the effect (easier starts), it does no harm to the engine. This is a lot cheaper than replacing fuel injectors. It reduces the cold start noise a lot.

The CR TDIs have a very sophisticated injection cycle, up to 7 injection events per power stroke. The design works well regardless of temperature. I have never had my glow plug light stay on for more than 5 seconds and the engine starts immediately and idles smoothly. I don't hear the nailing until I drive off. The CR is a fabulous piece of technology that has stupid easy cold start capability compared to my last TDI, a 96 Passat with a 1Z engine. On that beast I would have to wait around 30 seconds or more for the glow plug light to go off, crank & crank the starter as the engine rebelled against starting, then it would chug, cough, shake, sputter, and fight combustion while copious amounts of acrid white smoke came out the exhaust. The old Passat always started, but it sure was a damn ugly process.

Your car is fine and running as designed. Physics dictates cold temps and starting a diesel do not get along, even with all this wonderful technology. Drive more and worry less.

jrm said:

a 2014 should have the latest software, its common for them to buck and fall on there face between 0 and 35mph as the ECU fires the #4 injector on the exhaust stroke sending 1,200F heat threw the DPF to get it up to EPA regulations as quick as possible. If its truly undividable and not just annoying yours may have a sticky exhaust throttle, this unit creates back pressure as needed, but if stuck will be a huge problem- its located about midway on the system and has a unmistakable electric motor attached, you can take it apart and clean the carbon and rust out of it for free. Do a search on here, many in salt belt have had to do this.
https://forums.tdiclub.com/showthread.php?t=431512

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Scangauge-II or an OBD-II bluetooth plug widget hooked up to a smartphone app is your friend. You will see and learn amazing things on how the engine works. I have a Scangauge-II hooked up and monitor turbo EGT, DPF temp, turbo boost, and coolant temp.

The 23N5 update was simply to let the engine warm up more before it went into the catalyst 'warm-up' mode. During warm-up mode the boost will go over 15psi. That is a lot of stress on a cold engine and turbocharger. To keep the turbocharger boost down and gain coolant temperature during this critical time I keep the RPM between 2.5k and 3k. I don't up-shift until I'm over 2.5k RPM. High gears and low revs makes the turbocharger produce high boost, not good when it's cold. It might seem counter-intuitive to let a cold engine rev high, but it actually reduces the stress on both the engine and turbocharger. During a cold start, with high gear and low RPM, I will see ~15PSI during the catalyst warm-up mode. Using a low gear with high RPM I'll see ~7PSI. The turbo is heating up the catalyst system at the same rate. I'll see as high as 1250F on the EGT and 800F on the DPF during warm-up mode.

Monitoring the Scangauge-II, the catalyst 'warm-up' mode doesn't start until the coolant temp is at least ~80F in winter on average. The catalyst warm-up mode follows a map that the colder the start, the longer the coolant has to warm up before warm-up mode starts. At -10F the ECU waits until my coolant temp was over ~115F. Way past the point of the cold engine noise. The warm up mode is usually no more that 1 minute. I read my coolant temps off the Scangauge because it's accurate. The coolant temp gauge in the car is so buffered it's giving you something like a rolling 3 minute average.

Nobody has suggested in this time that it's a glow plug? Because that's what I would guess first. The glow plug light turns off fairly quickly but it is just a reminder light, it does not actually indicate when the glow plugs are on. This has been the case with most consumer diesels for decades - my 2000 Ford F250 is the same way. You can visibly see the headlights brighten up when the glow plugs turn off.

My next suggestion would be stiction eliminator, this helps some 6.0 Powerstroke engines that idle rough in the morning

N4TECguy said:

Nobody has suggested in this time that it's a glow plug? Because that's what I would guess first. The glow plug light turns off fairly quickly but it is just a reminder light, it does not actually indicate when the glow plugs are on. This has been the case with most consumer diesels for decades - my 2000 Ford F250 is the same way. You can visibly see the headlights brighten up when the glow plugs turn off.

My next suggestion would be stiction eliminator, this helps some 6.0 Powerstroke engines that idle rough in the morning

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There would a trouble light on if something was wrong with the GP system. Yes, there is some post start glow plug time. Even the first generation TDIs had it.

A burned out GP or two would result in very hard starting. The OP never reports that, only about the loss of power and pinging that goes on when the engine is very cold.

Mine has been doing the same thing this winter. The poor drivability lasts for about 1/2 mile and starts in temperatures below 20 degrees for me. With the recent sub-zero temperatures it was quite bad. I do use the Power Service Fuel Supplement with Cetane Boost. I had the 23N5 update installed immediately when it came out with no adverse effects. I did have my second turbo go several months ago, so that is the biggest change that I am aware of. No re-programming was done during that service to my knowledge. I need to put my ScanGauge II on and I lent out my VCDS cable. My heater core is going, so I may talk to the dealer if I bring it in for the warranty work.

OldLarry, since mine seems to be better than yours, you could try some PowerService in it (the white bottle for winter). I always get mine at Fleet Farm. I usually use about double the recommended dose, but I may up it as a test per BKMetz's comments.

Change the fuel filter....Quick and cheap....And treat the fuel...You might have gotten a wet batch of perhaps some leftover summer fuel.....Yes...Bad fuel can fill a filter in Minutes....
I'm guessing the filter...If you swap it when cold will be partially plugged with waxes and water....As the hot fuel from the excess return is pumped to the filter as a preheat, the filters flow gradually improved, then the car runs fine.
Is possible to park it in a semi heated garage?....If you can...Do this once...then also drop the line for the intercooler after it sits to drain any water out....(read that is more Jetta SPECFIC, so maybe not, sorry).

For me, I just changed the fuel filter at 50,000 miles service (even though it was not required) just before the cold set it. I dried out the bowl and then used the VCDS cable and laptop to run the fuel transfer pump. I started to wonder if I used a different brand, but it looks like I used an OEM filter from IDParts. That doesn't rule out having gotten a bad batch of fuel after having changed the filter. I did install a coolant heater and I think the car runs better after having been plugged in. I have only plugged it in a couple of times and don't remember. If I get motivated, I might try changing the filter again.

N4TECguy said:

Nobody has suggested in this time that it's a glow plug? Because that's what I would guess first. The glow plug light turns off fairly quickly but it is just a reminder light, it does not actually indicate when the glow plugs are on. This has been the case with most consumer diesels for decades - my 2000 Ford F250 is the same way. You can visibly see the headlights brighten up when the glow plugs turn off.


My next suggestion would be stiction eliminator, this helps some 6.0 Powerstroke engines that idle rough in the morning

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Stiction would not be the cause in a tdi. Our injectors are not hydraulic and therefore cold gummed up oil doesn't affect our injectors like in the fords. I've had Ford diesel engines and the archoil products work wonders on stiction but won't help a tdi.

People have had similar issues with the JSW's. There was a TSB for icing in the intercooler on those cars.

BarryT82 said:

People have had similar issues with the JSW's. There was a TSB for icing in the intercooler on those cars.

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The NMS Passat has an engine coolant to intake air intercooler so intercooler icing is not an issue.

ZippyNH said:

<snip>.As the hot girl from the excess return is pumped I to the filter as a preheat, the filters flow gradually improved, then the car runs fine.
<snip<

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I only have one hot girl, and have had her going on 50 years— not using her for this!

BKmetz said:

The NMS Passat has an engine coolant to intake air intercooler so intercooler icing is not an issue.

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Even though the NMS uses the W2A intercooler, i wonder if after some time there should be an inspection for EGR build up in the intercooler pathways that may cause this.

The CJAA and CEBA are know for massive ammounts of goo/sludge due to excessively cold IC condensing and collecting and thus freezing. But every time I've opened the jettas system up I've still noticed EGR sludge build up.

It's a cheap inspection and just another thing to rule out.

You could check, but keep in mind computer can control the intercooler temp very closely, preventing it from getting too cold and forming condensation.

-J

Rico567 said:

I only have one hot girl, and have had her going on 50 years— not using her for this!

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Lol...Love auto correct...I must start reading it over...And be in less of a rush. Then again..I I hadn't nobody would have laughed.