No Start / Crank No Fire - Loose Main EFI Relay Terminal Connectors

Electricalintermediate✓ OP Confirmed

Problem

Car cranks but does not start - no fuel pump activation and no spark. The Main EFI Relay was not being energized by the M-REL signal from the ECU. A previous owner had installed a jumper wire from the IGN fuse to pin 1 of the Main EFI Relay as a workaround, which masked the real problem and eventually fried the AEM V-1 aftermarket ECU's M-REL output.

Engine cranks but will not start (no fuel or spark)Main EFI Relay not clicking/energizing with key ONNo power to +B and +B1 circuitsAftermarket ECU (AEM V-1) unable to communicate with laptop via serial even with key ONErratic engine break-up on boost (secondary symptom from jumper wire damage)Engine stalling at idle (secondary symptom from jumper wire damage)

Root Cause

The female pin connectors inside the Main EFI Relay terminal socket (in the fuse box) had become loose and were not making solid contact with the relay pins. This caused the M-REL 12V trigger signal from the ECU to not reach the relay coil with enough voltage to energize it, even though the Black/Orange wire tested good end-to-end when unloaded.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted December 2022 on SupraForums.com