DriftDamage

The car is an 89 240sx I bought with a DE swap. Ever since I bought the car it would at times (generally only during the day on hot days) randomly shut off. Then it would always start back up 15-30 mins later when the car cooled down.

I was never able to find the issue and thought it would be resolved after I replaced the engine and did an SR20 swap thinking any hack job wiring would be resolved.

Well now that I have the SR20 in there it seems to happen more often im guessing because under hood temps are hotter with the turbo.

When the car shuts off it will start right back up if I have brand new ECCS and EGI relays on hand. If not then it will start up within 15-30 mins again as I stated above. So this says to me it has to be on these circuits as the car will not start unless both relays are replaced at the same time. Or atleast it seems that way.

I have taken apart the relay box and checked the wiring underneath the ECCS & EGI relays and there are no signs of burns for a short.

I thought it might be the fuel pump but I traced the wires and the wires dont seem to be bare or shorting. I tested it today with a multi meter at the covered connection right before the fuel pump and the ground wire comes up at less than 1 ohm. Voltage also comes out normal showing me it is grounded properly... atleast I think, somewhat of a noob with using the multimeter.

I tested the ground on the MAF and it also reads less than 1 ohm.

Looking at the wiring diagram and considering this issue has been present since before the swap it makes me think that certain parts on this ECCS/EGI circuit are not the issue since they have been replaced.

The fuel pump is new
KA Ignitor replaced with SR ignitor
Distributor was obviously replaced with the SR CAS and there's no single ignition coil since the SR has individual coil packs for each spark plug.
KA MAF was replaced with SR MAF

This leaves me with:

Resistor/Condensor
Power Transistor
Air Reg Solenoid

No fuses are popping. Everything else in the car still works perfectly before and after this issue rises.

This only happens when whatever is failing becomes heat soaked making it that much more difficult to trace.

So my questions are...

Where is the resistor/condensor on an SR20 or does it still have one? (I did not do the swap nor wiring so I am not sure where it is. But I was told everything that was stock was left on the car) If the SR20 still has one where is it and what does it look like? I can't seem to find it anywhere

Should it still have a power transistor after the swap? If so what does this do and yet again, where is it and what does it look like?

Where is the Air Reg Solenoid and would this even be something that would cause the car to shut down? I highly doubt it but might as well ask.

Is there anything else on these circuits I am missing?

Lastly how else could I find what is causing this? What do I test and how do I test it?

Any help would be greatly appreciated.