TD4 Crankshaft Sensor ?

I've just finished a bit of a rebuild on my 2003 (52) TD4 - the clutch had gone so I dropped the engine and box, replacing clutch and flywheel. All good - except now it won't start

Whilst the engine was out I removed the inlet manifold and painstaking cleaned the inside -gallons of Mr Muscle, Gunk and brake cleaner. I also pulled the injectors out and gave everything a good clean, resealed them. I've connected everything back up, and today had a go at starting it, expecting it to fire up after a few turns (prior to pulling it apart it started on the button every time) - but no, no luck. It turns over, and after about 5 mins of trying it started to fire - but it won't catch and run. The Haynes manual says the BMW engine is self priming, so I assume there is nothing I need to do to further bleed the system ? I've tried starting it on and off for over an hour (trying not to over stress the started motor), but it still won't run. It will fire but dies straight away. The longer you turn the engine over for, the less it fires. Let it stand for a couple of minutes with ignition off and then crank it over and it tries to start and will do for 6 or 7 attempts. Then it stops trying. But then it might start trying again ! I've checked every electrical connection, fuel line connections, vacuum hose connections - all seem to be fine. Resorting to a web search, I've now done a leak back test and all is fine, no fuel coming out of the top of the injectors.

The other thing that keeps coming up when I search for TD4 won't start is the crank sensor (I understand the Camshaft sensor can also be problematic but usually only when the engine is hot ?). Is there a way to test the crank sensor or do I have to buy a new one to find out ? I've just taken the starter out and removed the crank sensor so can test it on the bench if I know what to look for.

Anything else I should be checking ? The fact this has happened after I've put it back together makes me think its something I've done, but I've checked everything, even taking things like the inlet ducting and hoses back off to get better access.

Its starting to drive me potty

I'd check the sensor on the right of the engine block (as you look from the front) under the manifold, it's the one tuning chips plug into, fuel pressure sensor?
Dead easy to knock it or plug it in the wrong way round if you've been messing around in there. That would stop the engine starting.
Mike

Thanks Mike, went out and had a check but its all good.

While I was out there I plugged my code reader in and took some live engine readings with the ignition on. Should have written them down, but from memory the fuel rail pressure was 101.4, the low pressure was around 369 and the high pressure was 0 (zero). I assume this only goes live when the engine is running or is this the fault ?

There was another "strange" reading, the air flow was showing something like 3267.5 with the ignition on, engine not running (obviously !). Shouldn't this be 0, or at least very close to 0 ? I have not touched the MAF, just put a new filter in !

The MAF reading is a curious one. LP pressure is fine.
HP pressure will only show correctly when the HP pump is being turned by the engine.

It would be worth changing the HP regulator O rings.

Thanks Nodge. Any idea what the HP reading should be when the engine is being cranked on the starter ? I tried it just now and saw about 44,000 before the battery power went and the diagnostic reset. I will try again later but it would be good to know what I should expect to see.

44,000 Kpa while cranking is ok, I think

Mine shows 26,000 Kpa while idling.

I might open a new thread about HP pump parameters, see if theres a definitive answer out there . I just checked mine again and the reading says "HP Rail" and the reading whilst cranking had dropped to 31,729. Still sounds like enough to start it if yours is 26,000 idling but I want to be certain. I've no doubt the pump would benefit from a rebuild, but that can come later once I know why it won't start

The HP rail pressure is controlled by the ECU. It does this by modulating the HP regulator. This is the same regulator where the O rings fail. The ECU regulates rail pressure as needed. There is a theory that a failed and not opening injector could cause high rail pressure.