John.
Here's a link for a pattern for cam crank etc... on a Pico.

http://www.ilexa.co.uk/forum/index.php/topic,18473.msg91377.html#msg91377

Confirms you should see an amplitude of 4.5V on your crank sensor.

Are you getting the poor amplitude at the sensor plug or at the ECU plug? - the 1.9 PD is prone to chaffing it's engine harness where it runs across the starter motor / bottom hose, this causes all manner of sensor malfunctions - seen boost pressure, CTS, CPS signal issues due to this fault, green death usual to be seen seeping from the harness.

Also had a SDI Golf with a defective engine ECU, No DTC & no signal at the injectors, sent it off for testing to Actronics (usually pretty good) - they sent it back & said it was fine, a phone call revealed their admission that there is no substitute for testing on the vehicle - a new ECU cured it, again there was no signal at the injectors. doesn't explain your low amplitude on the cps though, (just a thought - you haven't left an attenuator in after testing the injectors have you - giving you a poor CPS pattern> I did once)

I have seen these shut down single injectors when a misfire is evident logging a DTC of "inj - malfunction in circuit", maybe a possible head harness earth path issue stopping all 4x??

Just for info - I've had a PD with a Tandem pump fail completely - the engine still started & ran with reduced performance off the 1 bar supplied by the tank pump.
I've also had PD's with in tank pump failure & they won't start at all. The Tandem pump is incapable of pulling the fuel through.

Jon