Port engine burning 20% more fuel

Twinbrook

Member
Apr 7, 2014
33
Middle River, Md
Boat Info
1998 Sundancer 370
Engines
twin merc 7.4 MPI''s
1998 Sea Ray 370 Sundancer with 454 MPI Horizons. Approximate hours -600.

Port engine burns 20% more fuel at idle and underway compared to starboard engine. Had a scanner checking for codes and data. There was an error code for a faulty TPS. Also the port engine "surges" up and down in idle or less than 3-4 knots. Neither engine burns any oil at all so I'm not concerned about valves and rings - yet. Also when engine was scanned and throttle was put at full wide open the TPS registered that it was only at 85% open. Port engine need more throttle to bring rmp's up to same level as starboard.

Could this be the cause of my fuel burning issue?
 
I'd say yes ECM is making fuel adjustments and your burning too much fuel.
 
Do both motors get up to operating temps?

Low coolant temperature can increase fuel consumption.
 
Port engine temp per gauge operates at 170 and starboard at 165. Did not use an IR gun to measure the block temps but I'd say that they are this temp reading once warmed up when I'm leaving the dock.
 
Looks like coolant temp isn't the issue. One motor would have to be significantly cooler, like around 120° to affect fuel trim.
 
Did you test or replace your TPS? At idle the TPS voltage should be approx. 0.5V and at WOT the output voltage should be near 4.5V. If the TPS is open or shorted the ECM should set Code 22.

Your symptoms are pointing to a faulty or loose TPS.
 

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