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G4+ randomly losing crank trigger and spark.


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Hi all,

Having issue with my 32GTR running a pnp g4+

It’s been in the car for at least 6 years, About a week ago the car randomly cut out while driving and wouldn’t start again. After leaving it for a few minutes it fired back up and got it home. 
Few days went by and while idling it cut out again. Plugged in the laptop and wasn’t getting any trigger scopes while cranking. Assumed a bad sensor crank sensor and fitted a few one.
After fitting, it cut out while idling. Again no trigger on the scope, I also went to test the ignition and fuel. Injectors would fire but no coils. At this point it also wouldn’t connect to the laptop.  After a few minutes I tried again after cycling the ignition and the coils were now firing. Went to crank it to see if I was getting a trigger and it stared and running fine
I’ve changed the ECCS and the ignition relays, checked all earths and still having the same issue.

could it be a fault in the ecu or am I missing anything ?   

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Sounds more like a power supply issue.  Assuming the trigger sensors are powered by the original CAS circuit, this comes from the ECCS circuit, whereas the ignition coils are powered by a separate relay.  However, both the ECCS relay and the coil relay are controlled by the same trigger - pin 16 (ecu grounds this pin), so since both of these weren't working, my suspicion would be on the control side of these relays.

Pin 16 is controlled by the ign switch signal on pin 45.  It is relatively common to see a low voltage on that ign sw wire, especially if the stock fuel pump controller is being used.  If it drops below about 7V then the ECCS and coil relays wont be engaged.  The low voltage is often caused by wear on the contacts in the ignition switch.   

When you next have a loss of triggers you could check if 12V is present at the cam sensor, if not then measure voltage on pin 45.  The ecu will often still power up without the eccs relay working as there will be enough current through a backfeed somewhere.  

If you find good voltage on pin 45, but pin 16 is not being grounded by the ecu then it could be a damaged fet or diode in the ecu, but the G4+ eccs circuit was pretty robust so I wouldnt suspect that yet.

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