I have been trying to fix this problem for 3 months with the help of 2 mechanics. Nothing has worked so far. I'm hoping you guys can help steer us in a good direction.
We launched our boat Memorial Day weekend and again in mid-June for several hours on the water with no problems. We launched again July 1. This time, I could not get the boat on plane. The engine RPM won't go above about 2800 to 3000 no matter how far I push the throttle. Engine sounds fine at idle and low RPM. Even sounds OK at 2800, it just won't go any higher. The engine only has 220 hours on it.
Over the span of 3 months several things were checked and repaired/replaced. In all cases we launched to test and there was no improvement in performance.
The marine mechanic scanned the engine and there were no fault codes. He collected engine telemetry while on the water under load and the sensor data looked OK. There are no alarms and the computer is not reporting being in Guardian mode.
Here is what we did:
1. Replaced spark plugs (even though they looked fine)
2. Replaced fuel filter, filter disk, and lower fuel pressure regulator (FPR had some black debris on screen).
3. Checked fuel pressure at rail. It was OK (~42 psi at idle)
4. Professionally cleaned fuel injectors (in case debris got in them).
5. Replaced some rubber fuel lines in case they were internally degrading (gas tank to Cool Fuel module)
6. Inspected gas in case it was contaminated (it was clear and uniform).
7. Checked exhaust path shutters in Y-pipe (in case they broke/got stuck and were blocking exhaust) - they were OK.
8. Checked manifold vacuum: it was low (12 in HG at idle)
9. Performed compression test and leak down test. There was leakage, so heads were removed and resurfaced and valves and valve seats were ground down. At this point I should mention the engine overheated 2 years ago and the exhaust manifolds were replaced at that time. The mechanic believes the overheat warped the heads and caused the leaks.
10. Replaced gaskets on heads, and intake manifold.
11. Replaced the entire distributor (screw mount cracked)
The head repair was quite expensive ($2500) and did not fix the problem. I'm getting pretty discouraged at this point. We are trying to consult with a Mercury rep to get some guidance. Not sure if we'll get any.
My thoughts are starting to drift to the stern drive. Could the gearing be failing and holding back the engine RPM? The props are original and look fine (no damage).
I can't even conceive of what else to check. Any guidance or advice is appreciated, especially if someone has seen this problem on this particular engine (5.0L MPI with PCM/ECM-555 computer)!
We launched our boat Memorial Day weekend and again in mid-June for several hours on the water with no problems. We launched again July 1. This time, I could not get the boat on plane. The engine RPM won't go above about 2800 to 3000 no matter how far I push the throttle. Engine sounds fine at idle and low RPM. Even sounds OK at 2800, it just won't go any higher. The engine only has 220 hours on it.
Over the span of 3 months several things were checked and repaired/replaced. In all cases we launched to test and there was no improvement in performance.
The marine mechanic scanned the engine and there were no fault codes. He collected engine telemetry while on the water under load and the sensor data looked OK. There are no alarms and the computer is not reporting being in Guardian mode.
Here is what we did:
1. Replaced spark plugs (even though they looked fine)
2. Replaced fuel filter, filter disk, and lower fuel pressure regulator (FPR had some black debris on screen).
3. Checked fuel pressure at rail. It was OK (~42 psi at idle)
4. Professionally cleaned fuel injectors (in case debris got in them).
5. Replaced some rubber fuel lines in case they were internally degrading (gas tank to Cool Fuel module)
6. Inspected gas in case it was contaminated (it was clear and uniform).
7. Checked exhaust path shutters in Y-pipe (in case they broke/got stuck and were blocking exhaust) - they were OK.
8. Checked manifold vacuum: it was low (12 in HG at idle)
9. Performed compression test and leak down test. There was leakage, so heads were removed and resurfaced and valves and valve seats were ground down. At this point I should mention the engine overheated 2 years ago and the exhaust manifolds were replaced at that time. The mechanic believes the overheat warped the heads and caused the leaks.
10. Replaced gaskets on heads, and intake manifold.
11. Replaced the entire distributor (screw mount cracked)
The head repair was quite expensive ($2500) and did not fix the problem. I'm getting pretty discouraged at this point. We are trying to consult with a Mercury rep to get some guidance. Not sure if we'll get any.
My thoughts are starting to drift to the stern drive. Could the gearing be failing and holding back the engine RPM? The props are original and look fine (no damage).
I can't even conceive of what else to check. Any guidance or advice is appreciated, especially if someone has seen this problem on this particular engine (5.0L MPI with PCM/ECM-555 computer)!
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