Passat 1.9 TDI: Hard Starting Problems & Fixes

Hello!

I'm reaching out to you because I'm at my wit's end.
My Passat is very difficult to start when it has been sitting for a longer period. Often, I have to crank it for 10 seconds or longer before it sputters and reluctantly comes to life. However, if I try to start it again immediately, it starts up as if it were brand new.
The problem is not temperature-dependent!
When it finally runs, it runs smoothly, quietly, and exactly as it should.

About the vehicle:
Passat B5.
115 hp, 1.9 AJM PD (one of the first common rail diesel engines).
Approximately 385,000 km.

What I have tested/done so far:
1) Anlasser/Batterie überprüft: Beim Start 2. Fahrzeug dazugehängt, sowie Temperaturfühler G62 abgesteckt (Kaltstart simuliert). KeiA refinement.

2) Disconnected the dual temperature sensor and had it checked at the workshop - the values are normal.

3) Have the error memory read - It was empty, except for the error code related to the disconnected sensor. That error code has been cleared.

4) Have the idle correction values checked, starting from cylinder 1 and decreasing to cylinder 4.
-1.13
-0.66
0.59
1.18
I'm not sure exactly what those values mean, but the mechanic from the workshop said that values below plus or minus 2 are normal.

5) Return line before the diesel filter, clamped off with a grip pliers.
I think he'll arrive faster.

6) Run the engine and, after stopping it, smell the oil filler cap: There is no smell of diesel.


I suspect that air is getting into the diesel system somewhere. There are no visible leaks under the car, and the tandem pump and diesel filter appear dry.
What's wrong with my Passat? The only thing that comes to mind is the seals of the PD injectors, but that seems unlikely given the correction values and the lack of diesel smell. Besides, I'm a bit afraid of disassembling the PD injectors.

Does anyone have a suggestion?

Sure, here is the translation of the text from German to English:

"Best regards,
bonsai"

If you're looking for air leaks or faulty zero-point sensors on the injectors, you shouldn't just have the idle speed control read out; you need to access a different set of data. Don't simply replace the PDE (positive displacement element) based on suspicion alone.
Unfortunately, this is a topic that is relevant to the diagnosis, and that brings us back to the point:

Quote:

We cordially invite you to participate. The requirement for posting in topics related to diagnostics (everything for which a vehicle diagnostic system is needed) is... a diagnostic tool from a diesel mechanic's shop, or... our software, including KDataScope, KPower, or the Diesel Mechanic license. a vehicle diagnostic support key. Diesel mechanic customers receive enhanced support (expert assistance) and full access. "The quick brown fox jumps over the lazy dog."

Here's a tip for an alternative method that doesn't require VCDS. However, this method requires a different specialized tool:
If you're looking for air leaks or leaks in the fuel line of such a motor, check the fuel pressure of the tandem pump using a suitable pressure gauge (VAS 5187) according to the instructions. You can also use the search function in the forum for more information (e.g., target values). We have discussed this topic occasionally in the past.

Hello Steffen,

Thank you for your help.

To stick to troubleshooting without a diagnosis:
If I understand correctly from the various threads, you need to remove the intake manifold, connect the pressure gauge to the tandem pump, then start the car and rev it up to 4000 RPM.
The required pressure should be at least 10.5 bar.
If not -> disconnect the return line.
As pressure increases, the PDE may leak.
If the pressure remains high, the tandem pump will break.

I also read in another thread that the early PD engines, like my AJM, have a sealing ring between the tandem pump and the cylinder head that tends to become porous and leak with mileage, and this can then cause air to be drawn in.

Wouldn't this then cause the same symptoms as defective PDE seals?

Sure, here is the translation of the text from German to English:

"LG" is an abbreviation for "Liebe Grüße," which means "Best regards" or "Best wishes" in English.

Oh, kids...
"3.5 bar at 1500 RPM and 7.5 bar at 4000 RPM for that model. Yes, the intercooler piping needs to be removed for lengthwise installation."
That must be a proper pressure gauge. For example, a glycerin-dampened model, or the original. Otherwise, the needle will just jump around wildly, and after the measurement, you'll know just as much as you did before.
If the target value is not reached, during the measurement, check the return line. If that doesn't solve the problem, it's either the pump or a blockage in the fuel line. If the gauge jumps high, then there's a leak before the point where you disconnect. Since the AJM Passat doesn't have a fuel pressure relief valve, the O-rings or the injector itself are likely the problem. This brings us back to using VCDS, which might help you pinpoint the specific injector. Use the BIP function for searching.
In this case, you're faced with the question of whether to reinstall the worn-out injector bodies (referring to things like spray patterns and pump pistons) or to buy new ones. However, the cost of new ones adds up to about the price of a used Passat AJM. Plus, you'll also need to replace some stretched screws.
If the target value is reached, you already know that you don't need to look any further.
Then we'll move on to engine mechanics...
There are AJM engines that have a rubber gasket like the one you described. Later models have a metal gasket. If you actually need to replace the pump, you will only be able to get the newer version. For example, Pierburg only offers the newer version, and it will fit without any problems.
Elring, for example, offers both metal and rubber gaskets individually.
Have you understood the basics? I'm talking about the crankshaft speed, which is the relatively accurate number of revolutions per minute, and not, for example, swapped car batteries. And that brings us back to VCDS...

Hello Steffen,
Thank you again.

The workshop where I had my car checked is a VW workshop, so they should have the pressure gauge there. I hope I can get by with a small donation to the coffee fund and borrow the gauge.

If the pump doesn't reach the minimum pressures that you corrected, does the entire pump need to be replaced, or can a seal kit solve the problem?

I only managed to start the engine by using jump leads and disconnecting the G62 connector. Even then, it struggles to start (with a noticeably higher starter motor speed).


I have noted all the information relevant for diagnosis (e.g., MWB23, starter speed).

Sure, here is the translation of the text from German to English:

"LG" is an abbreviation for "Liebe Grüße," which means "Best regards" or "Best wishes" in English.

I would still like to remove the starter motor, disassemble it, clean it, lubricate it with grease that doesn't harden, and then reassemble and reinstall it.

Hello!

I was at my mechanic's shop today, but unfortunately, they couldn't fix the pressure gauge.
For that, he hooked my Passat up to the testing machine again (just for information).

MWB 23 delivers very good readings. The maximum deviation is +32 on cylinder 1 at approximately 3500 RPM, while at idle, the values are more in the range of -17 to +5.
The starting speed is 210 RPM - This is the measured motor speed at which the starter motor rotates the engine when the connector for the PD control is disconnected.

I believe that a minimum speed of 280 RPM is essential, so I tried to remove the starter.

BUT HOW THE HELL DO I GET IT OUT???

I managed to remove the two screws from the starter motor myself, and also one screw from the motor mount (at the bottom). However, I can't get the nut off for the positive terminal on the starter motor, and I can't seem to do it with anything. Do I really have to disassemble even more parts to get to it?

Sure, here is the translation of the text from German to English:

"Lg" is a German abbreviation that stands for "Liebe Grüße," which means "Best regards" or "Warm greetings" in English.

If you see the mother, you can usually find the offspring. With VEP TDI engines, there's no problem, but I unfortunately don't have the specifications for PD engines in mind.

I'll try again later, I'll get under the car and give it another shot. Yesterday, I gave up after 30 minutes of trying without success.

What's still puzzling me is that my Passat also starts poorly, even with a jump start and the temperature sensor disconnected.

Could it be that the connection points for the body mass and the starter cables are already so corroded that they have too high a resistance? Or is the problem with the soldered cable on the starter itself?

For the return flow, I will get a transparent hose today.

Does it always need to have diesel in it, even when the engine is turned off? Also, what is a normal amount of air in the return line?

Sure, here is the translation of the text from German to English:

"LG" is an abbreviation for "Liebe Grüße," which means "Best regards" or "Best wishes" in English.

Okay, I managed to get the starter out with the help of a knee and a long extension.

I disassembled and cleaned it, sanded the friction surface of the collector, scraped out the grooves, and lubricated everything.
It still has the original VW markings and numbers. The starter is from Bosch, and the production date is 08/99.

Then it was reinstalled, and the grounding points between the engine and the body, as well as between the body and the battery, were cleaned.

In the workshop: 210 RPM. No rotation was faster than it was before being removed.
It looks like we'll need a new starter.

Hello!

I just wanted to quickly post the solution to my problem here, so that the next person who encounters it doesn't have to spend ages searching and potentially replace expensive parts.

After replacing the starter, which didn't improve the situation, I replaced the two O-rings on the tandem pump and then had the fuel pressure checked at a VW service center.
7.8 bar at 4000 rpm.
4.2 bar at 1500 rpm.
No change when the return line is blocked.

I then installed a transparent hose on the return line from the tandem pump and the diesel filter.
When the engine was running, the hose was milky white, meaning it was full of air. When the engine was stopped, there was an air bubble approximately 10cm long in the system.

So, I removed the diesel filter, and lo and behold, the internal seal of the diesel filter was completely damaged.
Okay, I quickly drove it around to bleed the diesel filter, reassembled everything - and now there's no more air in the return line.

And the Passat is running again!

Thank you for your help!