Stumped - Vito W639 not firing on one cylinder

[jonnyl]

Hi, I am stuck on this one.
The W639 Vito only fires on 2,3&4.
The injectors have been removed and tested. With a lot of time an patience I removed the glow plugs from 1 and 2 and the compressions are 300psi / 20 Bar on both.
no engine light, no fault codes with icarsoft 1.0

With injector 1 connected it does not fire but produces white smoke (- un-burnt fuel?,) disconnected it is clean.
So I swapped injectors and the fault stays on cylinder 1. I think this proves that fuel is getting into the cylinder and its not the injector.

So with good compression and fuel why wont it fire? Valve timing? is it possible for one cylinder to have different valve timing to another??
Could it be ECU injector timing? - I would have thought if its OK on 3 of the cylinders the chances are all 4 would work.
Is there anything that could affect cylinder 1 in isolation? inlet path? EGR? (On one old car the brake vacuum pipe connected from one cylinder, that caused a lot of head scratching when the servo leaked!)

Can anyone help me from going in circles?

 

[DaveE320CDI]

Have you checked the wiring plug to injector for broken wires or bad connection?

 

[jonnyl]

Thanks for the reply Yes it all looks OK. I think the connection is alright as it is making a difference, if it is connected or not, from the white smoke.

 

[grober]

Most injectors are ground switched that is they are supplied with a constant 12v with ignition on and fired by earthing them thro a transistor in the ECU--- CHECK FOR 12V ON ONE OF THE PINS OF INJECTOR 1 WITH IGNITION ON. lots of videos on youtube about this. otherwise its a wiring /connector fault or an ECU switching TRANSISTOR problem with that particular injector cicuit

 

[jonnyl]

Thanks Graeme, good thought but the circuit checks out OK and connecting a bulb on the injector plug shows it's getting the pulses OK

I got another glow plug out and the compressions are 310, 330 and 320 psi - is this about right for this engine?

 

[jonnyl]

I tried a running compression test and I think the answer is low compression on 1.

Cy1 325psi Cy2 450

So I think I have the answer. Interesting that cranking vs running produced such a variation.