West32
Active Member
- May 24, 2017
- 215
- Boat Info
- 1999 Sea Ray 370 EC Hardtop
Raymarine Axiom Pro system,AutoPilot,Radar,VHF,XM,Mercury Engine Gateway
- Engines
- Twin Mercruiser 8.1 Horizons with ZF Hurth Transmissions
OK, this has been a battle for a friend of mine with the Exact same engines I have and we have tried everything to fix his problem. 1998 Sea Ray 340 Express Cruiser with 454 Horizons. We take it out, it jumps on plane and runs great. He throttles up to 3800, runs great and sounds great. He goes to 4000 and the port motor has nothing more to give. Starboard goes to 4400 and the port stays at 4000, 4100 with throttles all the way down. Fuel Flow on the Rinda is 1.4 GPH higher on the port than the starboard motor at 3400, and 2.4 gph higher on the port than the starboard at 3800
We've replaced the fuel pump, fuel pressure regulator, plugs, cap, rotor, wires, sent in the fuel injectors for cleaning and flow tests. I've swapped coils, ignition modules, and Map Sensors. We replaced all the Fuel lines from the Tank to the Fuel Pump. Replaced the Fuel Pressure Regulator as well. Started motor and fuel pressure was 38 psi. Revved motor and went up to 43. Base timing was checked at 8 degrees.
Ended up doing a compression test and found all cylinders low, and a few around 100 - 110. Did a leak down test and found intake valves were leaking. Pulled the heads to find extreme carbon buildup in the heads holding the valves open. Took the heads in and had them gone through. No deformation of seats or valves, just Heavy carbon. They went through everything and we got them back. Put everything back together, timed it to 8 degrees and took it out. SAME exact problem. over the course of 2 weeks, we swapped computers, sensors, throttle bodies to no avail. For shits and grins, I arbitrarily advanced the distributor to see what would happen. BIG difference! Fuel flows were inline with each other right off the bat. AND we got both motors up to 4550 RPM. Both engines sounded great. I then checked the base timing. 18 Degrees. I then checked the total time at 3000 rpm at 48 degrees. WTH? With my Rinda connected, we took it back up to WOT and there was NO knock, no knock Retard No pinging. Everything ran great. Once we were back in the slip, we checked the vacuum at idle 12 inhg. At 2200 rpm it settled in to 20 inhg. I am absolutely baffled with this one..... Why is it running so good...? What are we missing?
We've replaced the fuel pump, fuel pressure regulator, plugs, cap, rotor, wires, sent in the fuel injectors for cleaning and flow tests. I've swapped coils, ignition modules, and Map Sensors. We replaced all the Fuel lines from the Tank to the Fuel Pump. Replaced the Fuel Pressure Regulator as well. Started motor and fuel pressure was 38 psi. Revved motor and went up to 43. Base timing was checked at 8 degrees.
Ended up doing a compression test and found all cylinders low, and a few around 100 - 110. Did a leak down test and found intake valves were leaking. Pulled the heads to find extreme carbon buildup in the heads holding the valves open. Took the heads in and had them gone through. No deformation of seats or valves, just Heavy carbon. They went through everything and we got them back. Put everything back together, timed it to 8 degrees and took it out. SAME exact problem. over the course of 2 weeks, we swapped computers, sensors, throttle bodies to no avail. For shits and grins, I arbitrarily advanced the distributor to see what would happen. BIG difference! Fuel flows were inline with each other right off the bat. AND we got both motors up to 4550 RPM. Both engines sounded great. I then checked the base timing. 18 Degrees. I then checked the total time at 3000 rpm at 48 degrees. WTH? With my Rinda connected, we took it back up to WOT and there was NO knock, no knock Retard No pinging. Everything ran great. Once we were back in the slip, we checked the vacuum at idle 12 inhg. At 2200 rpm it settled in to 20 inhg. I am absolutely baffled with this one..... Why is it running so good...? What are we missing?