Lupo: Won't Start? VW TDI Troubleshooting Guide

Hi everyone,

I've been a long-time reader and now I need your help with a Lupo 1.4 pump-injector TDI, 75 hp, with 230,000 km on the clock.

Error occurrence / Error description:
He started as usual after the first lap. I drove for 800 meters, and then suddenly he started sputtering, and the engine almost stalled. I then made it to a friend's place (another 200 meters) and was able to turn him off there. Starting him again only worked after a very long cranking, and even then he wasn't running at full power, but it was enough to drive the 1000 meters back home.

It remained the case that it only started playing music after about 30 seconds, and very reluctantly at that.

Eventually, it wouldn't start at all, and even a jump-start and a cranking speed of over 300 RPM didn't make any difference.

That's the current situation.
Please provide the German text you would like me to translate into English.


I've been researching in this forum for days, but so far without success.

What I have already checked (the classics):

-Relay 109: I'm getting a signal from the glow plug relay and can communicate with the engine control unit via VCDS, so it's ruled out for now.
-Pre-lift pump: When I turn on the ignition, I can hear it humming behind me in the tank. Fuel quickly reaches the fuel filter in the engine compartment, so that also seems to be working correctly.
-Knackfrosch: I have already replaced the K-filters and the Knackfrosch unit, but the problem persists.
- Tandem pump: It was leaking oil from the bottom. I then re-sealed it, cleaned it thoroughly, and carefully reassembled it, but this didn't solve the problem.
-Diagnosis revealed: All temperature sensors provided plausible values.
Once upon a time, in the FSP of MSTG...
P1570... Immobilizer fault, but likely caused by a very weak battery.
and once.
P0321: Crankshaft speed sensor (G28) - implausible signal. However, this code did not reappear after being cleared, and I was able to read its values through the measurement blocks. It also showed plausible values during startup, so it's actually okay.

What I have done so far:

"Once, just for fun, I let the Lupo pull me along, reaching speeds of about 20-30 km/h, and then I put it in second gear, released the clutch, and suddenly it came to life and started running."
At first, it was completely normal as I expected, but after driving about 500 meters, it felt like it wasn't running on all cylinders. It jerked, sputtered, and vibrated very strongly.
I could press the accelerator pedal, but the engine speed wouldn't go above 1000 RPM, and then it eventually stalled and wouldn't start again.

After sealing the tandem pump and filling the entire system with fresh fuel by repeatedly activating the ignition, I attempted to start the engine again.
"The organ cleaner didn't work. So, I used the good old Star Pilot and sprayed it in front of the throttle body, where the EGR valve is located. The Star Pilot caused the engine to rev up, and after spraying for 2 seconds, it started."

It idled smoothly and responded very well to the throttle. I really thought that problem was fixed, and that the tandem pump was the issue. It ran so well that I decided to take it for a test drive.
This time, I managed to go about 2 kilometers before it started stuttering and jerking again, and eventually cut out completely.

In my opinion, there's an air leak somewhere, which is why I got a clear hose. When I disconnected the return line from the fuel pump, I got drenched in diesel; it was spraying everywhere. I had turned on the ignition a few times before, which activated the pre-lift pump, but I didn't expect there to be so much pressure built up.

The transparent hose connecting the metal pipe on the engine to the "Knackfrosch" (presumably a fuel filter or similar component) showed that when the pre-pump is activated, air bubbles measuring 2cm in length originate from the engine. When starting the engine, foam appears. After removing the "Knackfrosch," the filter is completely full and pressurized, causing diesel to spray out.


I'm starting to run out of ideas, so here are some questions:

"How can it be that the engine starts when jump-started and with starting fluid, but not when using the starter?"

Do you think a bypass around the "Knackfrosch" (presumably a component or device) might help it start, since that would allow all the air to be vented and prevent it from being reintroduced into the system?

What else would you check?

"What could be the reason why it simply won't start, despite everything? I mean, it's a diesel engine; there's air and fuel, and the thing should run, right? I always assumed that these engines weren't very sensitive and would actually always work..."

This is my first post, and I've tried to cover the topic as thoroughly as possible.

Thank you very much to everyone who takes the time to read everything.

Best regards,
Peter.

Does the timing belt fit?

Quote:

Does the timing belt fit?

The timing belt was replaced about 60,000 km ago; it's unlikely that it would suddenly skip a tooth, right?

So, I had already removed the top cover, and everything appeared to be normal from what I could see.
Unfortunately, I don't have any tools to check the timing belt right now, but it probably isn't coming from the timing belt itself, because it was running at a completely normal idle with the starter motor engaged, and otherwise it seemed to be working normally until it started sputtering again after about 2 kilometers.

Greetings.
Peter.

Hi there,
This is a diesel engine, so please don't use starting fluid or anything similar. The ignition with that stuff will happen somewhere early in the cycle, but not necessarily within the top dead center (TDC) range. This can cause a shock to the mechanical components and the belt drive.
An engine scan would be helpful as always, especially since this involves diagnostics.
It seems the fuel injection system is not properly bled. It's possible that the lift pump is also drawing in air. The tank vent is clear, and the filter in the tank as well? Run the lift pump for a while until no more air comes out.
hg
Herbert.

Quote:

It seems the fuel injection system is not properly bled. Possibly, the lift pump is also drawing in air. Is the tank vent clear, and is the strainer in the tank also clean? Run the lift pump for a while until no more air comes out.

.

Worn-out pressure discs or guide rails in the transmission are also not uncommon with high mileage and can cause similar symptoms.

Karasa wrote:

Quote: Does the timing belt fit? The timing belt was replaced about 60,000 km ago; it's unlikely that it would suddenly skip a tooth, right?

Okay, I suspect it's the AMF engine; to my knowledge, there wasn't another 1.4 TDI offered in the Lupo. The AMF has a maintenance interval of 60,000 km... so it would definitely be worth checking and potentially replacing it!

Best regards.
Pretzelmann01