When a Mercury EFI V6 outboard or SportJet motor begins to stumble at idle, hesitate under acceleration, or lose top-end power, one of the first components to check is the Throttle Position Sensor (TPS).
 
This small sensor sends a precise voltage signal to the ECU that tells it exactly how far the throttle plate is open. If the signal is even slightly out of specification, the ECU will miscalculate fuel delivery, resulting in rough running, sluggish throttle response, or wasted fuel.
 
To diagnose and correct TPS settings accurately and repeatably, we offer two harness options:
Buckshot Racing #77 Mercury EFI TPS Test & Adjust Harness
Genuine Mercury/Quicksilver OEM TPS Test Harness (OEM part numbers 816085 and 91-816085)
 
Both harnesses plug directly into the EFI control system and TPS connector, allowing you to connect a standard digital multimeter and watch TPS voltage in real time. This live feedback lets you adjust the sensor back to precise factory specifications, restoring smooth idle, crisp acceleration, and optimal fuel economy.
 
The Mercury OEM harness 91-816085 is the factory tool. The Buckshot Racing #77 delivers equal performance, both supplied with clear, detailed step-by-step instructions. Choose the option that best fits your toolkit and preference—either way, you get reliable, repeatable results.
 
Compatibility is broad, covering all Mercury Marine V6 2-stroke EFI outboards and SportJets equipped with front-mounted throttle-body TPS connectors. This includes the popular 2.5-liter EFI series—such as the 135 HP, 150 HP, 175 HP, XRI, Mariner Super Magnum, Pro Max, 150 HP, 200 HP, and 225 HP EFI models—as well as the larger 3.0-liter EFI series like the 225 EFI, 250 EFI, 300 Pro Max, and 300X models.
 
It is also suitable for SportJet applications, including the 105, 140, 210, and 240 models.
The only exceptions are Mercury EFI engines that use the horn-style intake systems (found on race 2.5-liter and 2.4-liter Bridgeport models) and later DFI/Optimax and Verado platforms, which use different TPS connectors and integrated sensor systems.
 
TPS Testing Instructions
Disconnect the TPS from the EFI harness, and insert the test harness (either Buckshot #77 or Mercury OEM) between the two.
 
Set your multimeter to read low DC voltage. Disconnect the TAN/BLACK head-temperature leads from the port cylinder head. Turn the ignition key to the ON position without starting the engine.
 
Loosen the TPS mounting screws, rotate the sensor fully clockwise to the closed position, and measure the voltage.
 
For most models, the correct closed-throttle setting is 0.240–0.260 V. If the reading is outside that range, rotate the TPS slightly until the voltage falls within spec.
 
Tighten the mounting screws to 20 in-lb (2.0 N·m).
 
Slowly move the throttle from idle to wide open while watching the voltage rise smoothly to a maximum of about 4.16 V.
 
Any sudden jumps or drops indicate a worn TPS that may need replacement. Once the readings check out, remove the test harness, reconnect the TPS directly to the EFI harness, and restore the TAN/BLACK temperature leads.
 
Whether you’re maintaining a nimble bass boat powered by a 2.5L EFI or tuning a 3.0-liter, these harness options ensure your TPS and ECU are in perfect sync.
 
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.