not sure where this question should go!

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not sure where this question should go!

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Afternoon all.
Codger junior is carrying out a body shell transplant on his Nissan Silvia (1990's vintage) and has hit a snag of an electrical nature.
As it isn't a Fiat I can't put the question in the right place, but this is more of a general question anyway, so here goes.
He has transplanted the engine, gearbox, and wiring loom from one car to another, and the engine will not fire. We have a spark, and we have fuel, but the voltage at the injectors is only about 5v.
The "body" wiring loom cam with the shell that he is transplanting in to and has been hacked about a bit.
The ECU is no connected to anything metal other than via the wiring loom.
I have a shot in the dark feeling that there could be a poor or non-existent earth somewhere. So here is the general question - If I connect one of the ecu brackets to an earth by means of a separate lead, so that I know it has an earth, could I do any harm to the ECU?
Any other suggestions gratefully received as at this rate I am not going to get my drive back for the foreseeable...
 
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I would normally expect a metal ECU body to be earthed. But one of the wires in the plug will be an earth, make sure it earths somewhere.

Is 5v correct/incorrect for the injectors? A lot of systems in cars use lower voltages, and 5v is common.

Does it have an immobiliser in the ECU? If so, are you using the original key that goes with the ECU?

Is the fuel fresh, and is the pump creating enough pressure, rather than just supplying fuel.
 
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Hi Nigel. Thanks for your thoughts and ideas.
I will check the ecu earth via the loom, but could I run a temporary earth to the casing? Would it do harm / good?
I will check on the voltage requirement for the injectors. It could be that it is correct.
Immobiliser- good point! I am told the key and lock set is all as it was originally, but i will double check.
Yes the fuel is fresh and seems plenty of pressure, as I discovered when I pulled the pipe off in the engine bay and it went quite a long way!
 
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Transferring running gear from Rps13 to Ps13. The "old" one is a hatch with pop up lights and the "new" one (which is actually older) is a saloon with long flat head lights and tail lights.
 
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Quick update.
Engine now running.
Cam position sensor which hadn't been touched decided ro give up.
A new one and re charged battery and the beast lives again!
Just got to finish welding the inner arches now.
 
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