Van was running fine until Thurs when, after turning it off for a few minutes it was dificult to start. this happenned twice. Once started it ran fine until I got it home then wouldn't start at all.

Plenty of spark.

A friend told me that spraying choke cleaner into the throttle may enable it to start and this worked but it ran really rough and finally stalled.

Changed fuel filter and symptoms remained the same.

Took off the air intake plenum, fuel rail and injectors and did what I could to clean them as well as all the electrical contacts. Once I put it all back together it would start sometimes without priming with choke cleaner but once started ran on only 2 cylinders. It runs solidly on the 2 cylinders, won't stall but clearly not adequate and still way to hard to start.

Does anybody have any ideas.

I Removed the plenum again and examined the plug to injectors – found all the wires frayed and shorting together. I applied electrical tape to remove the shorts then reinstalled the plenum. Still won't start without squirting the air intake first with choke cleaner but now all cylinders appear to be working equally badly. It dies out with sudden acceleration but if I accelerate slowly it will rev up ok.

If anyone has had any experience like this I would really appreciate some advice.
Many thanks.

I would buy a replacement wiring harness for the injectors, the repairs to the wiring is not adequate for the signal required for the injectors to work. You should be able to get one at the dealer although you may want to check the aftermarket as it may be cheaper. You may also have problems with the connectors themselves.
There is a tool out there that will allow you to test each injector individually to see if it is working properly and if the connection is good. Unfortunately I saw it on Two Guys Garage and don't know who makes it. It seems that this is where your problem is coming from since the spark is good and you are getting fuel. You may also want to check the codes in the computer to see they will give you an indication as to where the problem lies. Just turn the key on and off and on the third time leave it on, the check engine light will give you the codes by flashing the numbers. If you don't have a book they are easily found on the internet. Hope this helps!

Bought a $45 pressure gauge kit and found fuel pressure to be only 10psi. Bought fuel pump ($170) and replaced (hard work). Now it appears to be ok. Pressure is up to about 40psi.

Great! Expensive but got the job done. I would think about replacing that injector harness though as the splices may fail due to the heat that they are exposed to.