Engine Car stalls after 10 mins of idling

I have a problem with my 1990 5.0 if anyone can input that’ll be dope. I have a current stalling issue during idle. Around 10 mins my car would start to surge and finally stall. I have a t5, 306 w/ gt40 heads upper and lower gt40 intake manifolds, stock valves from stock 5.0 heads. B303 cam. Cold air intake, Stock exhaust with cats, replaced tfi from autozone, msd distributer, Amazon plug wires, motorcraft spark plugs and Amazon ignition coil . It has no smog pump nor egr , egr is sensor is bypassed. At idle I’m getting 14-15 on my wideband. Made sure to calibrate as well. I’ve done a tps reset base timing @10 degrees btdc. I have New tps iac spark plugs fuel injectors, fuel pump, good oil/fuel pressure @ 39psi, bottom end was fully rebuilt. Couldn’t find any vacuum leaks. Checked fuel and ignition system wires for resistance. I need of help.
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Will it restart immediately without issue?

Start here

When it dies before you try to restart and with the key still on do you hear the fuel pump running?
Do you restart without turning the key to the off position?
that checklist should find the issue, you likely will have to do most of the testing when it dies before you turn the key off.
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after it surges and eventually dies all I hear is all the relays clicking and don’t hear the pump running. I actually tested the voltage at the fuel pump relay when it dies and found that it cuts the power to the relay when the engine dies. I have the key still on the on position and I am able to start the car when I crank it on but I have to give it gas to keep it running after that. I do have a fuel gauge installed and I does show 39 psi until the engine dies. Haven’t checked the spark yet
Will the computer talk to a code reader or test light?
These are all questions covered in the checklist.
Do the checklist when it dies.
Actually, the 'surging idle checklist' is the one to do:
The relays clicking make me wonder if it's an intermittent electrical fault. Do you know which relays are clicking? Is it the fuel pump relay under the seat, or some of the relays/solenoids under the hood?
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So the wire that goes to the fuel pump from the fp relay under the seat is getting 12v constantly. only until the engine dies, i hear the relays being de-energized than I no longer receive 12v to the fp. My fuel pressure guage continues to have pressure even when the engine dies so I doubt is a fuel related issue.
Also my afr guage is showing 13-14 upon startup. After 10 mins of idling-Right before it dies and starts surging is when the gauge fluctuates between 15 and 18 but I think it’s because the computer wants to compensate for the crazy surging. Just something I’ve observed for a while now
So the way the fuel pump relay works is that the ECU controls the negative side of the relay. It completes the ground to activate the relay. The positive side of the relay is fed by the ECU relay which also feeds other relays on the car.

I bet your issue is the EEC power relay mounted next to the ECU.


Zoomed in on the fuel pump circuit.

As you can see, the eec relay feeds the fuel pump relay as well as other solenoids.

What that said, why the eec relay is dropping out is a different story, but first see if you can confirm that the relay is the issue. You should have constant power on the black/orange at all times, and key on power on the orange/black and red wire coming out.

It could be a bad relay, a bad connection or even a bad ignition switch.
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I understand that fuel system and I’ve checked the eec and fuel pump relays . I don’t suspect it is a fuel issue only because while observing my fuel pressure from startup to when the car stalls I’m getting 39 psi . And also I have done a continuity check on the fuel system wires and checked out good.
Also correct me if I’m wrong but wouldn’t I get a lean mixture if it was a vacuum issue? My aem afr gauge stays between 13-14 until it starts surging, readings will fluctuate. Should I be looking in another direction?