I'm new to the forum but a long-time Touareg 4.2 V8 FSI owner with experience wrenching on these engines. I purchased a non-running 2008 Q7 4.2 V8 FSI with 122K miles that absolutely wouldn't start for the previous owner. I've exhausted forum searches and my own knowledge trying to fix it, so wanted to see if the community has any ideas.

New battery was installed and vehicle cranks but doesn't fire. A scan shows a P0322 (Engine Speed) code that's common on these 4.2s with failing Crank Speed Sensors. I swapped the engine speed sensor with a new Bosch unit and cleared DTCs, and the P0322 code immediately comes back and engine doesn't fire. Thinking it might be a bad sensor, I bought a second Chinese sensor from Autozone with the exact same results. I then tried wiggling the ESS wire at the connector to the main harness while a friend cranked the motor, and the engine periodically fired off briefly and abruptly died. Assuming the wiring harness connector itself was bad, I then cut and crimped a new female connector to the wiring harness, with exactly the same result (P0322 code and cranking).

Before I pull the passenger intake and start disassembling the main harness, are there any other known failure points on V8 Q7's that lead to a crank sensor DTC? Things like water ingress in ECU, the ESS wire in the harness getting pinched somewhere along the block, ETC? I'm just trying to run everything to ground before I take more of the car apart.

Thank you in advance for any ideas.

 

Check for power at the sensor plug.
Run a temporary earth strap from engine to chassis.
Get a look inside the hole for the sensor and look for anything unusual.
Check for fuel, spark and compression. Scrutinise colour of spark plugs.
Scroll slowly through measuring blocks for engine and look for any unusual readings such as temperatures that seem way off.
If it has an airflow meter, try unplugging it.
The ecu/modules rear right can get damaged by sunroof leaks.
The engine ecu can get flooded by a blocked plenum drain. Pour some water into that area and make sure water drains out underneath.
Reach out to Ross Tech.

 

Not claiming any special knowledge on the 4.2 V-8 motor, but I will say did you use VCDS to scan the car for faults or what exactly did you use to scan for fault codes; it needs to be a VAGCOM compatible scan tool, or you won't see anything besides the CEL linked hard codes, and so you are likely not really seeing the whole picture that could help you to diagnose the car.

Here's a link to Ross-Tech WIKI for that P0322 code, which is a generic, OBDII code, so that's why I am asking about your scan tool.

https://wiki.ross-tech.com/wiki/inde...6/P0322/000802