After a customer had destroyed his engine(wrong fuel), the engine was replaced by my colleague with a 2nd hand one from a running car. However, it won't inject or spark when starting. It concerns a 1996 Volvo 960 with the 3.0l 24V inline-6 engine, with the Motronic 4.4 system. The original wiring loom and ECU are used, both of which were doing well before.
There are no fault codes stored, and the CEL is off during prolonged starting.
There is no immobilizer on the ECU.
It is constantly on the charger and booster during starting, so low voltage is not an issue.
It is an automatic, but the P switch is not used and wired as 'always P'.
The injectors inject a few times when turning on the ignition, so the ECU is able to operate them. I can also operate each injector individually with the Bosch ESI tronic OBD reader. They don't inject after that anymore when trying to start. All ignition coils are provided with system voltage as soon as i'm trying to start, they are just not connected to mass by the ECU.
During starting, the RPM gauge does not seem to move at all, but it does work when operating it via OBD. On OBD the RPM is sometimes 90, sometimes 100 or 60 when starting. It does not vary during starting, though.
I have tried:
-Naturally, my first suspect was the crank sensor, but the flywheel is completely intact, and the (new)sensor gives a (good?) signal. (450mV triangle wave visible on the scope)
-The camshaft sensor(also new) also gives a good signal, being a clean square wave of several volts. I have measured both at the ECU with the ECU connected.
-I have used a new ignition module.
-I have used another ECU. (also without immobilizer)
Since there are no fault codes and no CEL, there should also be no NoStartCondition. There is a camshaft and crank signal at the ECU, so the ECU should know the engine's position and speed. The ECU is able to operate the injectors, but chooses not to do so. It is unlikely that the ECU is not able to operate the ignition, since the injectors are also not operated. It is likely that the engine's speed/position is not correctly received. It's likely something mechanically is amiss, since there are no fault codes.
Things I haven't tried yet:
Operating the ignition coils manually. I can't do that via OBD, and I don't know the signal that should come out of the ECU. Hence, I don't know what signal to give to the ignition module. If anyone knows, please tell. This would rule out the entire ignition system, leaving only the ECU and crank/cam sensor.
Here is the wiring loom of the concerning systems. It's in dutch, so if you have a question about a component, i'll translate. I've marked the most important ones already. I hope it's visible.
So my question is: What could be causing that the ECU does not fire the injectors, and does/can not fire the ignition?
I hope i'm overlooking the obvious here...