Passat TDI: Slow Start, Troubleshooting Guide

Someone from my circle of friends bought a 1995 TDI Passat with the 1Z engine. The plan is to use it as a commuter car during the winter and then, starting in the spring, it will be used for a year-long study abroad program in Moscow. It's on track to reach 700,000 kilometers (approximately 435,000 miles).

The vehicle appears to be in good condition for its age and mileage, and the technical inspection is less than eight weeks old. It was purchased from a private seller for what I consider to be a rather high price.

I was asked to describe the starting problem here and I hope to get some ideas. The 90 hp TDI engine starts well when warm, but the sound is rough, although it runs smoothly. It feels a bit sluggish and the response to the accelerator is somewhat slow, but noticeable. The maximum speed, according to the speedometer, is not quite reached; it's about 10 km/h short. This could also be due to the age of the car, and it wouldn't be a problem for the owner. There's a cloud of black smoke during startup, followed by about 10 seconds of blue smoke (which smells strongly of diesel exhaust) and then it doesn't reappear. When starting with full throttle when warm, there's a cloud of black smoke that disappears again from around 2500 rpm.

The cold start is quite poor, even though (according to measurements) all the glow plugs are working. The engine only starts after about 10 seconds of cranking, and initially, it barely responds to the accelerator. You need to let it run for at least 20 seconds before it starts to run properly. During this time, there is significant blue smoke, which decreases after about a minute. The oil consumption is approximately 1 liter every 2500-3000 kilometers, and the fuel consumption is between 5.5 and 6.5 liters per 100 kilometers, with a 50/50 mix of city driving in Berlin and highway driving.

What I find strange is that when I open the fuel cap, a noticeable vacuum is released from the tank with a distinct hissing sound. If I only open the fuel cap a few turns, the engine starts after about half the time it usually takes, and the blue smoke disappears after 10-20 seconds.

The fuel cap appears to be original and is not lockable. Does this tank have another fuel vent, or is it integrated into the cap? How can I free it up? And how many engine revolutions does it normally take for it to start? I seem to recall that these engines often need a few revolutions to start when cold.

"700,000 km is making me jealous; my 1Z only has 430,000 km."
The vacuum in the tank is not normal. The ventilation should go through the tank cap with a check valve, and there is also a separate vent with a gravity valve.
The starting behavior is likely also influenced by the engine's mileage, but I would still check the turbocharger settings and the injection timing. If the injection timing is too late, it can also cause blue smoke and reduced power. The turbocharger needs to be checked mechanically. For the injection timing, connect your VCDS diagnostic tool.
Sure, here's the translation:

"Best regards," or "Sincerely,".
Herbert.

I don't have VCDS. However, we are confident enough to check the timing using the timing marks (which ones, where?). The previous owner of the Passat used to drive a Seat Terra with the 1.4 VW diesel engine, and he did almost everything on that car himself. Eventually, he broke the engine mount, which had rotted away. Fortunately, this happened at home with 2 months left on the vehicle's inspection.

Regarding the fuel tank: Is it possible to disassemble the fuel cap or clean it somehow? Or would it be better to buy a new fuel cap? Where is the second vent valve located? The cold start performance has significantly improved with the fuel cap loosened by 1/2 a turn. He drove it back home about 20 minutes ago after dinner. Stopwatch: 8 seconds to engine start, and then it ran. By feeling the cylinder head, it was still slightly warm after 2.5 hours of standstill.

Hi,
Even the 1Z TDI is already high-tech. Nothing works without a special tool. You need a wrench for the belt tensioner, a ruler for the timing, torque wrenches, and VCDS for adjusting the ESP (Electronic Stability Program), and a dial indicator for the mechanical assembly of the engine.
The fuel tank cap must be able to be vented from the inside.
hg
Herbert.

If you are interested:
I think I still have the tools for setting up the scooter somewhere in the moving boxes (they should be thrown away anyway, since no one in the family rides a scooter anymore).

Also, my mom also has an ESP (Electronic Stability Program) module from a 1Z/AHU engine (a "dead" engine with a piston failure). It had around 120-130,000 km on it, but it's been sitting around for about 5 years now.

You should be able to find VCDS in the Berlin area.

Greetings.
Guste.

Hi!

As I mentioned before, the vacuum in the tank is not normal.
Let's start with that.

I have a 1998 TDI, ALH model, and it always starts immediately, or rather, in about 1 second, even with 300,000 kilometers on it.
Even if it spends the night outdoors in temperatures as low as -15°C.
It might have a slight tendency to stall, and the idle speed might be a bit high, but it's absolutely reliable.

The glow plugs are not as important at the current temperatures.
"With mine, several also broke over the years, and I didn't even notice."
It was just by chance, a few years ago when it was really freezing cold, and my wife had to work late at night, so I checked them just to be safe: 3 were defective.

Well, in that case, I would also use VCDS to check what the cranking speed is.
and what temperature values the temperature sensors provide to the engine control unit.

If things get really bad, you should have the engine's compression tested.
700,000 is a really extreme number.

I received an update via SMS: The gas cap had been removed, cleaned in an ultrasonic bath, and reattached.

Steffen G wrote:

Well, in that case, I would also use VCDS to check what the cranking speed is. and what values the temperature sensors provide to the engine control unit.

The temperature sensors often fail.

At 700,000 km, everything is suspect, at the very least...

Hi,

If you know someone who has a VCDS in Berlin, you know .

Right now, timing is just a minor issue, but if needed, we can certainly discuss it further via email.

Best regards,

Jan.

Quote:

The tank cap was removed, cleaned in an ultrasonic bath, and reattached.

Does the fuel vent work now? There are holes at the bottom of the screw cap that allow air to be drawn in.
The starting speed is not evaluated in the 1Z engine, as the engine and electronics are from a bygone era.
hg
Herbert.

I don't know if it made any difference. The Passat has been on its way to Sweden via Fehmarn since yesterday. I also don't know when I'll see it again.

But I find it remarkable and courageous at the same time, to drive such an old car, with so many miles on it, so carelessly over long distances.

When dealing with issues like misfires (1Z) or starting problems, it's important to also consider the possibility of problems with the crankshaft sprocket. This involves checking the timing, for example, using a TDI timing checker, and paying attention to the idle speed and sensor values.

Is anything changing here? Is the injection timing starting to drift in the default setting mode? Engine off, repair the crankshaft sprocket.

Best regards, Rainer.

Air in the system could also be an issue, although given the mileage, I would first perform a compression test before trying to diagnose any other problems.

As I wrote, the owner is on his way to Sweden. He probably doesn't see it as a big deal.

Hutfahrer wrote:

I don't know if it helped. The Passat has been traveling from Fehmarn to Sweden since yesterday. I also don't know when I will see it again. But I find it remarkable and courageous at the same time, to drive such an old car with so many kilometers on the odometer so carelessly over long distances.

In other countries, this is normal. Even crossing the Sahara, there is no cell phone reception, and there is very little traffic at night. I arrived safely in a completely rusted-out /8 Mercedes with 2 million kilometers on it. Here, many people worry too much, despite having the best cell phone network to get help, and there is also the "yellow angel" (emergency service).

Here's another tip: Carefully inspect the return lines of the ESD (Electronic Stability Device) and ESP (Electronic Stability Program). Even the smallest, barely visible cracks can cause fuel to slowly leak back into the tank overnight. They are relatively easy and inexpensive to replace.
Similarly, the ESP input shaft seal, which appears to be diesel-resistant, can still draw in air when stationary! I wouldn't be surprised if this happened after a certain amount of mileage.
Is there any visible air in the hoses of the DIFI-ESP system?