Seat Altea 1.9TDI BLS - very strange case - the engine does not start

[yarowsc]

Hi all mates.
Altea 1.9TDI BLS 2007 year of production. a very strange case, not everyday, I have never encountered such a situation. namely;
the starter turns, the engine does not start, when trying to start the starter, VCDS is connected to the OBD (no errors in the ECU, the fuel system is working properly), the ECU loses communication with the vehicle and the rest of the modules, immediately after which the radiator fans start. I turn the ignition off, turn it on again, the communication is correct, there are no errors in the ECU.
it's like that; three elements have a weird connection
- crankshaft sensor
- camshaft sensor
- unit injectors

and the situation is this;
VCDS connected to OBD, we shoot the starter and;
1. how to disconnect the crankshaft sensor, the reading of the parameters when trying to start the engine is correct, the measuring blocks show the rotation of the G40 camshaft.
2. how to disconnect the camshaft sensor, reading the parameters when trying to start the engine is correct, the measuring blocks show the rotation of the G28 crankshaft.
3. how do I disconnect the round connector from the unit injectors, the reading of the parameters during the attempt to start the engine is correct, the measuring blocks show the rotations of the G40 camshaft and the rotations of the G28 crankshaft.
of course, the engine does not start

replaced, almost all of the electrical parts on the engine have been replaced, sensors, throttle, EGR valve, starter, the entire complete electrical installation of the engine, ECU and still the same.

as soon as I disconnect one of these three things, is communication with the ECU when turning the starter and visible parameters and measuring blocks. like everything connected, when turning the starter, the ECU loses communication with the car, the radiator fans and VCDS will turn on also no communication with the ECU

I fix a lot of electrics and electronics, but I haven't had such a case yet
can someone suggest something? because my ideas are slowly coming to an end

[Mooti]

EDC knives are dead?

[yarowsc]

as I wrote in the post above - ECU already exchanged for a second, cloned, adapted next - various options were
still the same

[sebage]

It sounds to me the problem of imperfect contacts at high power consumption. Or loss of power / ground. I would try to separate the larger electricity consumer (the starter), to give him the necessary energy from elsewhere, not from the car network. This would be a first step, that is, a 12V from another source (there may be another battery), through thick cables, directly on the starter. Attention, directly on starters (do not use neither ground nor + 12V to pass through other components of the car, I mean, connect and + and - directly on starter). Try and say what ...

[Mooti]

just, and does the starter have 250-300rpm?
Or a stupid question, did you check the compression?
Did you open the valve cover?

[sebage]

Don't give him too many homework at once. He says that when the starter turns the engine on, it loses its connection to the ECU. So, for now, we don't have a "hotstart problem" or compression problem, it doesn't reach that stage yet. Remain at the idea of removing from the circuit of the largest consumer (the starter), which can influence in two ways: 1. introduce noise into the circuit, 2. create potentially differences unwanted .

[PSAcars]

Hello to all. Can you ( yarowsc ) measure the voltage on power pins on ecu during the key position start, one time I had problem with vw ignition barrel losing acc contact when rotating key to starter position.

[sebage]

The idea of PSAcars is a good one and to consider, the problem can be from there. So you (yarowsc) first do what he wrote because it's easier.

[yarowsc]

when I disconnect the control cable from the starter solenoid, turn on the ignition, the key in the "starter" position, communication with the ECU is correct (nothing breaks), in BCM I have a preview of all contacts 15, 30, 50.75 in the measuring blocks
it's already checked sooner

[PSAcars]

Hello to all. Did you try to put extra ( thick ) wire from battery to main fuse box of car, may be voltage drop?

[sebage]

What I wrote the first time, you tried. You mean to give 12V for starter from another source? Just for starter...

[yarowsc]

What I wrote the first time, you tried. You mean to give 12V for starter from another source? Just for starter...

I tried, another separate battery, two separate thick starter cables (ground, 12V)
no changes - still the same

[yarowsc]

everything checked, power supply at the ECU approx. (three thick 12V cables, three thick cables - ground, 12V pin 18)
at the moment, my conclusion is that the ECU does not allow the engine to start if three basic conditions are met, i.e.
- crankshaft signal
- camshaft signal
- signal to the injector pump
if I disconnect the circular connector from the injector pump, communication is when attempting to spin the starter.
and this is not the fault of the injector pump, outside the engine the original PD electrical harness is connected (same as in the engine head), the PD set connected to it and the situation returns. I will disconnect PD, it's ok (communication with the ECU is).
it is enough to connect one PD and the communication during turning on the starter is gone and the radiator fans turn on.

[DiegoStud]

681057
...you don't need G40 connected to start up one of these engines.

Some wires somewhere have chafed or shorted, or one of the supply relays is dying.

[Meat-Head]

Has anybody suggested that you go and push off!

[sebage]

I hope you did not fall into the trap of measuring voltages on the ECU without the load in the circuit. These would be irrelevant measurements. I would make the proposal to connect a long or short beam bulb between GND and pin 18 and on one of pins 3, 5, 6 of the K jack.
This would simulate enough consumption to find out if you have imperfect contact on the ECU power circuits. (none of the problems listed by you would have any reason to reset or inhibit the ECU).
Sorry if I put you to work extra, but from a distance, to get an idea as accurate as possible, you had to. Once again, sorry.

[Meat-Head]

If you short starter to battery with a piece of wire can you still commicate to ecu

[yarowsc]

I changed almost everything (sensors, ecu x3, starter, bordnetz, steering wheel module, ignition switch, relays - good that I have a stock of used parts in place). the last element to replace for tomorrow - a fuse box in the engine compartment. from this box the ECU is powered by a relay, which is controlled by the ground signal from the ECU

[Meat-Head]

ON TOPIC:-

get another car, jump cables battery + to + engine block to engine block
isolate using dk thanks

[Dunker]

Like PSAcars and Meaty said. I'd scope all powers and grounds at the ECU using battery earth for scope GND when ign off, ign on then cranking. Also scooe diag lines. If Comms is dropping and ECU locks for a short while with a new ECU it has to be power issue. Like meaty asked, does it bump off? I've had usual relay and wiring issues with these and also bad ign switches.

[autoden]

I had this some time ago but on a golf 1.9. The ECT sensor was shorted out. It then dragged the 5v system down.