Hi all

So I've got my dream 300XZ but the list of problems is quite long

 

The main fault I'm trying to diagnose and fix is missfire on cylindersl 1 and 2, two front cylinders as you look in engine bay.Fault is permanent cylinders don't fire at all.

I've spent few hours today and got to dead end,basically I've swapped ignition coils from other working cylinders and spark plugs - still no good,checked voltages on 2 faulty coils and there is +12v,earth,and continuous +12v on trigger pin of both ignition coils.Compared with other working coils and 12v on trigger pin should colapse for spark to take place.

OK checked continuity between coils and PTU all ok,checked trigger signal from ecu to PTU on PTU plug and there is no signal.This is where I get confused,because injectors on this cylinders are injecting fuel and continuity between ecu and PTU is ok.

Is it the CAS unit?

Why there is no signal from ECU

If it is, why this injectors are operating?

Finally I had to disconnect this 2 injectors to avoid petrol washing cylinders dry,

If anyone had simmilar problem please reply any help will be blessing,

I seem to remember 4 plugs are fed by one part of the loom the other two another piece. Can't remember if its the front two are seperate.

Your defiantly not getting any electrical signals to the injector or coil pack connectors?

how were you checking for signal from the ECU to the PTU?

 

with a 'scope?

http://www.300zx.co.uk/tech/manual/manual/diag/001.gif

 

 

I seem to remember 4 plugs are fed by one part of the loom the other two another piece. Can't remember if its the front two are seperate.

Your defiantly not getting any electrical signals to the injector or coil pack connectors?

 

I do get signal to injectors (checked with osciloscope and screwdriver)

On cyl 1 and 2 ignition coils i get no trigger signal

how were you checking for signal from the ECU to the PTU?

 

with a 'scope?

 

Yes, with scope,Just flat line on cyl 1 and 2 but for 3,4,5,6 voltage collapses I've also scoped CAS unit and it appears ok

ye, if it was the cas it would affect all inj and ign triggering, cranking FP running etc.

 

there

the next thing to do would be to back probe the ECU connector on the pins for the affected coil trigger signals and see whats happeing there. you might be lucky and simply unplugging and refitting the ECU plug is enough to sort a bad connection. it does get a bit damp down there..

 

if its ok then its a wiring fault affecting both cores for each PTU signal. have you stabbed the cores of the PTU plug with the scope in case the plug terminals are rotten/broken off?

 

i'd be surprised if it was the ECU as theres a separate transistor for each output, so both FETs would have to be dead, unless theres a common track thats gone O/C

 

but its definitely something O_o

 

i'd be surprised if it was the ECU as theres a separate transistor for each output, so both FETs would have to be dead, unless theres a common track thats gone O/C

 

 

sorry, im wrong, the FET's are in the PTU, thats the whole point of having it. I think its just a 5v sq wave trigger to the PTU if i remember right so it wont take much to cause grief.

this is a better pic

 

http://www.300zx.co.uk/tech/manual/manual/efec/013.gif

 

Finally got it running on all 6

The problem was wiring between ecu and PTU

Cyl 1 trigger was short with cyl 2 so they both did not spark,found it in piece of loom somebody made,and used bullet connectors,wires came out and got short to each other

I'm very happy now hearing her running on all 6,even did little drift today

Thanks for all help

great news :-)