ECU randomly shuts off at operating temperature

[Eric180sx]

Hello,

I’m dealing with a problem I’m not sure how to address. I’m hoping to receive pointers or guide on my quest to solve my issue. 
 

Issue: On cold start, my swapped 180sx with an rb25det will crank and idle normally, but as soon as it starts warming up. There’s a subtle backfire, little pops if you will. At operating temperature, the idle begins to fluctuate up and down. Eventually, it will drip my 150A breaker at the battery and the g4+ ecu will lose power and shut off.  Or it will shut off without dripping the 150A breaker and everything else stays on: radio, fuel pump, gauges, etc. 

Questions:

1. What may cause the ECU to turn off?

2. How to I measure voltage to the ECU? 
3. Is it possible there is a short causing the current surge to drip the breaker and make the ecu behave erratic? 
4. Anything I should check?
 

Parts installed before problem began:

• GTR R35 Coilpacks 

• Bosh donut knock sensors 

• PRP trigger kit 

• 270A alternator 

• LINK G4+ lambda wideband 

 

[Adamw]

I think the fact the 150A breaker trips sometimes suggests there is a vert serious short somewhere.   In the occurrences where the breaker doesnt trip, the short is probably just dropping the ecu voltage enough to cause the eccs relay to drop out.  There is nothing ecu or engine control related that would have wires big enough to trip a 150A breaker (the wires would catch fire first) so I would be looking more at the larger circuits such as alternator/starter/battery cables, etc.  

 

[DerekAE86]

Of the things you've listed the only one that could possibly do it is the alternator.

Did installing the new alternator require wiring changes? If not, what was the condition of the wiring and plugs?
It's possible that a plug was damaged or heat affected and now you've disturbed it by unplugging the old alternator and plugging in a new one it's created a high resistance short.

If it's shorting through a carbonized plug for example the resistence would slowly drop as it gets more heatsoaked (as the engine bay warms up) or as the current draw through the wiring increases (as your rpm goes up and the alternator outputs more charge current).

[koracing]

I've also seen on swaps where someone cleans and paints everything and then all the grounds are terrible because they are no longer bare metal contact.  I would definitely go over your power and ground connections and make sure they are all clean and free of paint or powder coating.

[Varinn]

Guilty! I did this on my engine swap first time I did it. Painted the block+mount arms but didn't clear the contact points of my ground straps. I don't remember what symptoms I had but cleaning my grounds fixed it all.