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Engine swaps, bolt-ons, tuning, OBD-1 conversions, forced induction, suspension & brake upgrades, etc.

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Postby Carder » Fri Nov 22, 2019 2:52 pm

Okay I have a P72 ECU with Neptune RTP Demon 2. The ECU has stopped communicating with all sensors, when I plug the computer in I get no feedback or readings at all.

When I turn the key everything powers up except the main relay. IT IS NOT THE MAIN RELAY!

WHY? I have an AEM infinity 506 and it works great. The fuel pump primes and the Car starts and runs great.

The P72 however will not power up the main relay.

What I am looking for is someone knowledgeable to help me figure out what needs to be replaced inside the ecu. All I have managed to find online is repairs for the IAT burn out I believe Q31 transistor (this is not the problem).

Again the signal that would activate the main relay is not there. I believe this is pin 7 Connector A on the OBD1 ECU, but have been unable to trace it past QM3 on the board.

Any help here would be appreciated.
Past rides: 88 & 89 Civc Dx, 90 Civic (sohc zc), 90 Civic Dx (B16-YS1),
1989 CRX Si (stock, red), 91 CRX Si (zc sohc, Tahitian green), 90 CRX (B16-Y1, burnt orange)
Currently: 1991 Honda CRX Si Restoration Project
Engine B20VTEC turbo previously dyno'd at 312whp & 306 ft/lbs (mustang dyno)
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Location: Windsor (area), Ontario

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