M52 Strange Problem - Best Answer gets a Scratch n Sniff

[Scrambler 7]

Basically its a fuel - fuel rail - injector malfunction that is temperamental.

So done me engine swap, the car runs sweet no issues then im getting this...

Took the injectors out and they don't seem to be pulsing when this issues going on. I got this weird blow back through the intake when I tried to start it today. Also the fuel pump kept on whirring like it wasn't getting any fuel but had plenty in tank. Sometimes it would whirr constantly and other times I turned the key on it would prime itself then stop like normal. On other random occurrences when turning the key on the injectors would squirt suddenly as soon as the key turned on... Im guessing thats what the blow back was, as the valves would be shut and the pressure from the injectors had no where to go but vent back through the air filter. I thought at first it could be fuel pump relay sticking but then why would the injectors not be pulsing?

Im guessing its a bad connection some where and ive heard that you shouldn't solder the wires on theses, is that true? as I have soldered just about every splice.

Regards