AHF ignition coil motor control unit failure - no start (solved)

I'm having another new problem with my A3 AHF.
Yesterday, I was driving on the highway and at 130 km/h, the fuse 29 (engine control) blew, and the car shut off.
"New fuses were installed, but it immediately tripped again when attempting to start. After about 30 minutes, the fuse was fine again. It would briefly start for 10 seconds and then shut off, and it hasn't started since."

The fuse is fine now, but the engine won't start.

The vehicle is currently still at the rest stop (hopefully ).
I'm going to read the error codes.
"Does anyone have any ideas about what might be causing this problem, so I can at least make it the 70km home?"

Regards,

EDIT: Relay 109 is new.
EDIT 2: If the valve is stuck in a fully closed position due to a malfunction, could the fuse blow due to excessive current draw?

Hello,

Okay, regarding your problem, it would be interesting to know if you can still access the engine control unit (ECU) at all. I doubt the fuse blows due to the fuel injection pump. Please read the error codes and report back.

Best regards.

Error code indicates: Upper limit sensor fault.
It doesn't really spray, even when connected to diesel lines; it only drips slightly.
The actuator is energized and switches.
"The diesel fuel is being drawn in well. I removed the ESP cover twice, and it ran correctly both times."
Rsw is at 0.760V, as expected, when the ignition is turned on.
Towing is not working, and the ESP lines appear to be okay.

Edit: The Rsw knob turns easily all the way to the stop and returns.

Instructions for finding a short circuit:
- Disconnect all sensors, senders (NHG), fuel injection pump, etc.
- Turn the ignition on and see if the fuse remains intact.
- Reconnect them one by one and observe the fuse.

Based on the error code, I suspect chafing or rodent damage to the wiring harness leading to the fuel injection pump.

Best regards, Rainer.

Yes, I suspect so too.
Problem: Unfortunately, the fuse is now completely blown.

Prior to the problem occurring, the screw on the high-pressure fuel pump (NHG) for the return line was loose, causing diesel fuel to leak through the connectors of the pump and the NHG.
After briefly drying the connectors, I replaced the fuse and started the device. It ran for about 10 seconds and then shut off again (blowing the fuse).
"The problem persists: the fuse keeps blowing, and nothing starts."

When measuring the resistance between pin 1 and pin 2, and between pin 2 and pin 3, I also got 0 ohms instead of the expected 5-7 ohms.
Could there be an error here?

Hi,
What exactly did you measure there? The needle valve actuator only has two contacts, and 7 ohms is not the resistance you'll find there.
hg
Herbert.

Oh sorry, I'm at the gas pump.
"Pins 1 and 2, and 2 and 3 on the pump connector should measure between 5 and 7 ohms, but I only read that somewhere once and measured it out of boredom at the rest stop."

Fuel injector connector = where? On the fuel injection pump? Round multi-socket outlet on the injection molding machine?
hg
Herbert.

Yes, of course, the connector on the fuel injection pump.
Slightly oval shape with 10 pins.

Error likely found.
While assembling the MSW, I was probably too rough, and now the first connection (the one near the pump wheel) no longer makes contact.
According to the search results, this appears to be either the power supply or the sensor for the quantity adjuster.
Unfortunately, the pump now needs to be replaced .

Hi Klaui!

I sincerely hope that the power amplifiers for the ESP (Electronic Stability Program) weren't disabled by the MStG (Motor Vehicle Act).
Because eventually, there will always be another, weaker link in the chain that gives way if the predetermined breaking point is repeatedly reinforced - of course.
This isn't criticism, just a suggestion: before replacing the pump or continuing troubleshooting, it might be a good idea to test the MStG (presumably a diagnostic tool or system) on a comparable vehicle.

Best regards from Munich!

Thanks for the tip. Before installing them, I would have at least briefly connected them and checked if the error memory could be cleared.
I hope this issue is resolved, but if not, I'll need to consider further repairs.

The vehicle is running again.

Hi Klaui!

klahaui wrote:

The vehicle is running again.

...well, it's still better than no answer at all, ABär.

Just don't be so terse. (Otherwise, something will always leak out of you everywhere ).
What exactly was the reason for that?
Did you replace the entire pump, or just a part of it? And did it start working right away, or did you have any issues?

Best regards from Munich!

Excuse me .
Yes, it was the pump, it has been completely replaced.
After bleeding the brakes and making a rough adjustment to the master cylinder, the system started working immediately.

Set to warm-up mode and everything is perfect.
The only drawback: the new pump injects 6mg/h in the lowest setting, while my old one injected 2.5mg/h. As a result, the engine feels a bit sluggish, at least to me.

The pump is a refurbished unit with a 1-year warranty, and the price is €350 for an exchange.

The change took approximately 2 hours.

"As I mentioned, a pin on the STG (likely referring to a specific component) was broken on the old pump, and I didn't want to try repairing it, so I got the 'new' one."

The fuel injection amount is now correct; after it had warmed up properly, it also read 3-3.5 mg/h.
The performance issue was due to slightly misaligned timing (crankshaft to camshaft), which happened because I didn't have a ruler when I changed the pump, so it was rotated just a little bit.
Now, it feels like it's performing just as well as it did before the exchange.
Going uphill, he shifts back into 4th gear as usual. Okay.

Best regards,