Background: 2001 Sea Ray, owned three years, purchased used. Boat typically used very heavily in summer skiing and tubing. Summer 1, boat used most of summer then water in oil - hair line crack in block. Short block replaced. Summer 2, (after break-in period) boat used most of the summer but, motor has characteristics of water in fuel. SeaFoam and HEET used (not at the same time) to address condition. Hard to get skier out of hole, but upon reaching 2200+ rpm - runs well at or near WOT. Summer 3, Motor is running rough, stalls when idling when warmed up. Hesitates, sputters going to WOT - if I can get past 2500 rpms it runs well. Initial thoughts maybe a sensor is bad - gave up on guessing and took it to a marina to read ECM and diagnose. After replacing MAP and fuel regulator - marina is informing me that value job is needed. I have scoured this forum for similar guidance. Looking for a second opinion, based on the data I have received.
Marina comments follow:
Motor is Mercruiser 4.3L EFI with TBI (throttle body fuel injection) with 473.3 hours. Short block replaced at approx. 400 hours ( my comment). There is no way to determine from ECM info as to when engine block was replace nor does it categorize hours run by RPM as the newer MPI engines do.
Rich running condition has been caused by two issues A. Bad MAP sensor and B. Leaking intake valves which are throwing off the sensors readings that establish air/fuel mixture in engine by ECM. Unfortunately, the leaking valves and corresponding loss of compression were masked by the fact that readings are substantially different when engine is cold versus hot. The problem is with both heads as cylinders #2, #3 and #5 are all loosing compression when hot. Problems with intake valves confirmed by performing "leak down test" on all cylinders and you can hear air flowing back through intake manifold.
Series of diagnostic events to determine problem were:
A. Boat battery dead upon arrival.
B. Engine running rich.
C. Diagnostics show fault code for MAP sensor - Replaced sensor. Fault code cured but engine continues to run rich.
D. Fuel pressure is too high 33PSI and recommended by Mercury to replace fuel pressure regulator. No change in fuel pressure with new regulator.
E. Baseline compression readings with engine cold register from 160 to 175 PSI in all cylinders which are within spec. However as engine warms up compression begins to drop in #2. to 115; #3 to 110 and #5 to 135. At this point performed Leak Down Test and determined Intake valves in those cylinders leaking back into manifold when engine running warm Which causes incorrect manifold pressure and increased fuel added to engine.
At minimum engine needs a complete valve job.
At first we were chasing fault codes, now I am looking at a valve job. Plans are to take it to another marina for second opinion.
Marina comments follow:
Motor is Mercruiser 4.3L EFI with TBI (throttle body fuel injection) with 473.3 hours. Short block replaced at approx. 400 hours ( my comment). There is no way to determine from ECM info as to when engine block was replace nor does it categorize hours run by RPM as the newer MPI engines do.
Rich running condition has been caused by two issues A. Bad MAP sensor and B. Leaking intake valves which are throwing off the sensors readings that establish air/fuel mixture in engine by ECM. Unfortunately, the leaking valves and corresponding loss of compression were masked by the fact that readings are substantially different when engine is cold versus hot. The problem is with both heads as cylinders #2, #3 and #5 are all loosing compression when hot. Problems with intake valves confirmed by performing "leak down test" on all cylinders and you can hear air flowing back through intake manifold.
Series of diagnostic events to determine problem were:
A. Boat battery dead upon arrival.
B. Engine running rich.
C. Diagnostics show fault code for MAP sensor - Replaced sensor. Fault code cured but engine continues to run rich.
D. Fuel pressure is too high 33PSI and recommended by Mercury to replace fuel pressure regulator. No change in fuel pressure with new regulator.
E. Baseline compression readings with engine cold register from 160 to 175 PSI in all cylinders which are within spec. However as engine warms up compression begins to drop in #2. to 115; #3 to 110 and #5 to 135. At this point performed Leak Down Test and determined Intake valves in those cylinders leaking back into manifold when engine running warm Which causes incorrect manifold pressure and increased fuel added to engine.
At minimum engine needs a complete valve job.
At first we were chasing fault codes, now I am looking at a valve job. Plans are to take it to another marina for second opinion.
