Engine (SDI) Won't Start After Tuning!

Hello!

First of all: I'm not a novice; I learned the trade as a car mechanic and have only been away from it for a year! The engine was running without any problems until then!

I need help from professionals!!!!

Seat Ibiza 1.9L SDI (Engine Code: AQM, 50kW - 68HP), Year: 2000.

I've experimented with powerbox tuning myself, and it worked well (approximately 1 kOhm resistance between pump connector pins 2 and 3).
However, since the engine control light was flashing on my car and the error code 'upper limit value of quantity control' was stored, and I didn't want to revert the modifications that were providing extra power, I had to come up with a way to trick the electronics during startup (because that's when it performs the self-test and detects the manipulation).
Since I had a used device at home, I opened it and saw a cable connecting pin 4 and pin 5, and I measured the resistance value.
I adopted this value for my own design/creation!
Bei eingeschalteter Zündung montierte ich die Box und es zog einen Kurzschluss (ein richtiger Lichtbogen war das) wo ich den Widerstand eingebaut habe (zw. Pin 4 and 5).

From now on, the car would no longer start, and there were 6 error messages that could not be cleared.
After that, I found a blown fuse (fuse number 3 in the fuse box located in the footwell, 15 amps for the motor).
Now, all but 3 errors can be deleted. The remaining error numbers are:
01282 Solenoid valve for throttle control flap N239 - Short circuit to ground.
17849 Exhaust gas recirculation valve N18 - Short circuit to ground.
Quantity setting, upper limit value!

We had the car towed to a repair shop.
The inspection revealed (as it did for me, I used the VAG diagnostic program) that the fuel injection pump is defective.
So, we exchanged them, but the car still didn't work, and the error messages remained.
After that, we also installed a new engine control unit and programmed it.
Now, the error related to the quantifier could be deleted, but the other two errors remained.
Even now, the car wouldn't start, even though:

new fuel injection pump
New control unit.
Mechanical faults have been ruled out.
Fuel reaches the fuel injectors.
and the throttle valve is open.

'That is, the engine is receiving air and fuel (the engine's valve timing and the fuel injection pump's injection time are correct), but it still won't start. All the fuses are okay (both inside the car and in the engine compartment)!'
Despite the other two errors, the engine should still run, right?

What else could it be? HHHHHIIIIIIILLLLLLLLLLLFFFFFFEEEEEE!!!!!!!!!!!!!!!!!!!!!

Injection start verified?
If so, how?

Best regards, Rainer.

It's possible that you damaged more than just the fuse; you might have also damaged some wires.
Please check all cables and components that are connected to pins 4 and 5, where you converted the resistance into light.

Injection start verified?
If so, how?

Greetings, Rainer

Hello.

No, the start of injection was not 'dynamically' checked because the engine is not running.
However, as mentioned, the basic settings and therefore the diesel pump are correct (at least they are set in a way that it should run). They are mechanically adjusted using a setting pin (which is also needed when replacing the timing belt to ensure the diesel pump is properly aligned).

It's possible that you damaged more than just the fuse; you might have also damaged some wires.
Please check all cables and components that are connected to pins 4 and 5, where you converted the resistance into light. }

Hello!

Yes, I had also considered that, but such a cable should be able to handle that current for a short time (since it's only fractions of a second until the fuse blows).
But I was thinking more about the crankshaft position sensor, as it has very fine windings and is normally used for determining the injection timing. But how should I test it? Perhaps a resistance measurement (continuity test)?
Now the question arises: if this component were to fail (resulting in engine stall), how would it cause the engine to stop (through a shut-off valve? or by throttling the diesel supply so much that the engine dies and won't restart?), because diesel fuel is being supplied, but is enough fuel actually being supplied?

Hi!
Based on my experience, he should definitely check the crankshaft speed sensor in the error memory. Otherwise, try to establish a stable voltage and start the engine with the diagnostic tool connected. Or simply try jump-starting it. Then, when the engine is running, it should become clear whether the crankshaft speed sensor is working or not. However, I don't think it's related to that...
I suspect there's actually a fault in the wiring, or perhaps a fuse is still defective (F23?!). Have you measured all the fuses, preferably under load? If things go really wrong, a defective fuse can be hard to spot with the naked eye. And what about the larger fuses on the battery? As far as I know, one of them is responsible for the entire control unit. However, if that's the case, you would likely see many more failures.

Good luck.

Hi!
Based on my experience, he should definitely check the crankshaft speed sensor in the error memory. Otherwise, try to establish a stable voltage and start the engine with the diagnostic tool connected. Or simply try jump-starting it. Then, when the engine is running, you should be able to see if the crankshaft speed sensor is working or not. However, I don't think it's related to that...
I suspect there's actually a fault in the wiring, or perhaps a fuse is still defective (F23?!). Have you measured all the fuses, preferably under load? If things go really wrong, a defective fuse can be hard to spot with the naked eye. And what about the larger fuses on the battery? As far as I know, one of them is responsible for the entire control unit. However, if that's the case, you would likely see many more failures.

Good luck.

Hello!

Thank you for your reply!

The diagnostic tool does not communicate with the control units during the startup process. I believe the crankshaft sensor would only be logged in the error memory if the engine is running, but I'm not entirely sure, and I'll check it as you suggested.
As mentioned, the fuses (for the motor) are all in good condition, as I replaced them as a precaution because, as you already wrote, a hairline crack could occur.

Hi,

To the best of our knowledge, in VP-TDIs, when the ignition is turned on, the pump control unit moves once to its maximum travel and back, which can be heard as a "click-clack" sound from the pump.
I'm just assuming that the same applies to SDI.

If you're not hearing anything like that anymore, you probably have a cable that's burned out: specifically, the positive wire at the output of relay 109, which connects to things like the volume control and the two magnetic valves mentioned, for which you're still seeing the error message "no power."

Solution: Run a temporary cable from the output of the 109 to pin 5 of the fuel pump connector (at least, that's where it should be on an AFN engine).

Or the pass-through test under load:
Turn the ignition on and hold a 21W indicator bulb between pin 5 of the pump connector and ground. The bulb must glow brightly – if it doesn't, the cable in question is broken.

Good luck with your further search. . .

Perhaps the cables first started to melt, and then the fuse blew.
Possibly, that's why the error is a short circuit to ground.

Hi,

To the best of our knowledge, in VP-TDIs, when the ignition is turned on, the pump control unit moves once to its maximum position and then back, which can be heard as a 'click-clack' sound from the pump.
I'm just assuming that the same applies to SDI.

If you're not hearing anything like that anymore, you probably have a cable that's burned out: specifically, the positive wire at the output of relay 109, which supplies power to things like the volume control and the two magnetic valves mentioned, for which you're still seeing the error message 'no power.'

Solution: Run a temporary cable from the output of the 109 to pin 5 of the fuel pump connector (which would be pin 5 on an AFN engine, at least).

Or the pass-through test under load:
Turn the ignition on and hold a 21W indicator bulb between pin 5 of the pump connector and ground. The bulb must glow brightly – if it doesn't, the cable in question is broken.

Good luck with your further search . . .

Hello!

Thank you for your tip!
I will work through all the tips mentioned here, bit by bit, next weekend, and I hope to have some success.