3.4 C2 turns over but wont fire

Hi All, I have recently acquired a 996 which I was enjoying very much but i parked it up the other day and it was running fine and now it won't start. It turns over strongly and all the lights/electrics work fine. I have checked the fuse box and nothing is amiss there that i can see. From my research it would appear to be either fuel pump or the CPS (crank position sensor) is there any way to trouble shoot or other suggestions i have missed? The rev counter/tacho doesn't move at all which i believe is a clue also. Thanks in advance.

Does it have an after market immobiliser on? Can you smell fuel from the exhaust after you've been turning it over? Need to establish whether it's a fuel issue or ignition issue. At a guess, if it's turning over rather quickly, then it's an ignition problem. Only my guess though.

Need to narrow down the fault by using diagnostics tool. I would check condition of a spark plug. Any wiff of fuel? Check fuel filter. List goes on.

As said, best to get a code reader on it. But if it's cranking without firing, and the rev counter isn't moving I would suspect the CPS. You can test it with an ohm meter to be sure.

Fuel, air, spark but modern stuff had far too many sensors for that principal to work easily. I'd agree crank position sensor definitely results in lots of cranking and no firing although normally these show fault prior such as cutting out particularly at idle. I'd be looking at that and probably also what any immobiliser cuts? Does it cut the fuel pump?

When the CPS went on my 996 it failed exactly as per OPs symptoms, just went out to the garage, no EML or any warning messages etc, just cranked over and over and would not fire. Never cut out before that time although I have had CPS faults on other cars before that would do that (Circa Y2K onwards MBs) I don't think you will get any fuel through if the CPS is faulty, there's no crank signal for the ECU hence it won't try and inject fuel. Mine didn't seem to smell of fuel when it had been cranked over which would tie in with that. But you should be able to hear the fuel pump prime when the key is first inserted. And I would expect the rev counter needle to move as the engine is cranked, even if there was no fuel delivery etc.

Thanks all for the responses. I have a basic OBD2 code reader so could try that. As i said, i have only just bought the car so have only done 250 miles in it but it ran perfectly up until this. There is no smell of fuel etc. The spark plugs are all pretty much new.... I guess fuel pump is the next in line. I don't have much time coming up so hoping for a quick fix (i just want to drive it!!!). also the security is factory with no additional immobilisers. Any further wisdom would be appreciated.

Some of the basic OBD tools still show live data such as engine RPMs, even if you are not sure about the rev counter it should pulse as it is cranked over. Plug it in and see if there's any stored codes - P0335 was what I had, and measured the ohms on the CPS which confirmed it. Was a pain to remove though, plenty of swearing and patience required although I got there in the end! New Bosch sensor from Autodoc - the Bosch part # is stamped into the CPS casing if you need it :thumb: Never had an issue since

Thanks all, the sensor is cheap enough that i figure replacing it is no great hardship so will try that and go from there.