325 ECU Removal & Tuning Prep — Support Bulletin

GT40 Marine | Doc GT40-SD-ECU-325-BULLETIN | Support Bulletin | Rev 1.0 — 2026-05-24

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When You Need This Bulletin

ECU removal on the 1630 ACE 325 platform is required for two workflows:

1. 325-specific intake install (GT40-SD-INT-325) — the intake adapter occupies the airbox-side bracket, forcing ECU relocation
2. Stage 2+ tuner installs (Magic Module, MaxRPM, similar) — most marine tuners require physical ECU access for the install procedure

This bulletin documents the ECU handling procedure for both workflows. Read in full before disconnecting any ECU harness.

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Fitment

Not applicable to 230 / 260 / 300 HP variants — those use a different ECU package with different removal procedures.

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Safety — ECU Handling

The 1630 ACE 325 ECU is more thermally and electrically sensitive than earlier platforms. Mistakes here cause permanent ECU damage that is NOT covered by GT40 warranty.

1. Battery disconnected before any ECU work. Confirm the battery negative cable is fully removed from the post, not just loose.
2. Static discharge precaution. Ground yourself against the engine block before touching the ECU. Wear an anti-static wrist strap if available.
3. Cool ECU only. If the engine has been operated within the last 30 minutes, wait for the ECU to cool before handling. Hot ECU + thermal shock from removal = silicon failure.
4. Connector handling. The 325 ECU main harness uses a multi-pin Hirose-style connector. Release the latch tab fully before pulling. Pulling without releasing the latch tab damages the pins permanently.
5. No exposed metal contact. Place the ECU on a static-safe surface (anti-static bag, clean cloth) after removal. Do not place on a metal workbench.
6. No moisture. Keep the ECU dry. Even a few drops of water on the harness side cause corrosion of the internal contacts.

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ECU Location on 325HP Hulls

The 325 ECU sits inboard on the airbox-side bracket. Specifically:

• RXP-X 325 / RXT-X 325 — port-side, just forward of the airbox, mounted to the engine bay sidewall with 2 M6 fasteners
• GTX Limited 325 — same general location but rotated 15 degrees outboard to clear the front service hatch

Photograph the ECU location and harness orientation BEFORE any disconnect.

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Removal Procedure (~10 minutes)

1. Disconnect the battery negative terminal. Verify with a voltmeter that 12V is no longer present at any harness pin
2. Locate the ECU and photograph current harness routing
3. Release the main harness connector latch (push the latch tab away from the connector body, then pull the connector straight off — do not rotate)
4. Identify the 2 M6 fasteners securing the ECU to its bracket (5 mm hex)
5. Support the ECU body with one hand while removing the 2 fasteners with the other — the ECU will drop slightly when the last fastener clears
6. Lift the ECU clear of the engine bay
7. Place the ECU on a static-safe surface — anti-static bag preferred, clean dry cloth acceptable

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Reinstallation Procedure

If reinstalling at the original location (e.g., after a tuner install)

1. Position the ECU against its original bracket, orienting the harness connector in the original direction
2. Thread both M6 SHCS through the ECU mounting tabs into the bracket
3. Snug both, then torque to 8 Nm (71 in-lb) with a 5 mm hex socket
4. Reconnect the main harness — push the connector straight on until the latch click is audible
5. Pull-test the connector — should not move

If relocating to a new bracket (e.g., during 325 intake install)

1. Install the new bracket per the install guide for the relocation kit
2. Position the ECU on the new bracket, orienting the harness connector in the same direction as the original install
3. Thread the relocation kit's M8 × 30 mm SHCS through the bracket and ECU mounting tabs
4. Torque to 18 Nm (13 ft-lb) with a 6 mm hex socket
5. Verify the harness has no strain — the relocation moves the ECU 50 mm port-side, so the harness routing must accommodate
6. Reconnect the main harness — push straight on until the latch click is audible
7. Pull-test the connector

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Post-Install Verification

After ECU reconnection (relocated or original):

1. Reconnect the battery negative terminal
2. Turn key to ACC — confirm dash illumination is normal, no fault codes on initial wake
3. Wait 30 seconds for ECU boot
4. Start engine briefly — confirm normal idle, no fault codes after 60 seconds
5. Scan with BUDS or compatible OBD diagnostic — verify no new fault codes
6. Fault code P0606 indicates an ECU communication issue — likely a harness connector not fully seated. Disconnect, inspect pins for damage, reseat.
7. Fault code U0100 indicates an ECU-network communication failure — likely the same harness issue. Same fix.

If fault codes persist after harness reseat, contact GT40 Marine support before further operation.

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Tuning Workflow Notes

If this ECU removal is part of a tuner install:

• Tuners that require ECU removal typically also require a "first key cycle" after install — turn key to ACC for 60 seconds, then to OFF, then start — to allow the tune file to load into ECU flash
• Some tuners require the battery disconnected for 30 minutes AFTER tune file load to allow ECU memory commit — verify your specific tuner's procedure
• The 325HP factory ECU has a higher boost ceiling than 230/300 — Stage 2 / 3 / 4 tune files written for 230/300 hardware will NOT work on the 325 ECU. Verify your tune file is 325-specific before install.

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Warranty Note

ECU damage from improper handling is not warranted by GT40. Specifically excluded:

• Static discharge damage
• Connector pin damage from improper unlatching
• Thermal shock damage from hot-ECU removal
• Moisture damage from wet handling
• Damage from incompatible tune files

This bulletin is provided as install guidance only. The customer assumes responsibility for ECU handling.

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Connects to

• GT40-SD-INT-325_COLD_AIR_INTAKE_INSTALL_GUIDE.md — primary use case for ECU relocation
• GT40-SD-STG1-325_STAGE1_KIT_INSTALL_GUIDE.md — Stage 1 master sequence-doc

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Support

• Email: support@gt40marine.com
• Site: gt40marine.com
• ECU-specific support: include the GT40 kit SKU, hull HIN, current fault codes (if any), and photographs of the ECU mounting in any support correspondence

Built in the United States. Designed for buyers who want the best.

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This bulletin is © 2026 GT40 Marine. All rights reserved.