Fixed!! EFI problem solved mercruiser
06-09-2025 | 06:32 PM
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From: Las Vegas
Fixed!! EFI problem solved mercruiser
Well it was the fuel pump (mostly)! I changed the fuel pump on the Mercruiser 5.7 EFI last week and took it out to the lake on Sunday. I also changed the spark plugs just to be sure. Instant power, no bogging under load and crisp throttle response without any hesitation along with a super smooth idle and no shuddering. My 2001 Stingray 220 LX with 475 hours, 23 inch 3 blade prop, 3 people, ice chest and a heavy toolbox, 107 degrees at Lake Mead did 61 mph GPS. Not bad.
But I think I can get more because of the rpm. Right now I max out at 4285 RPM from a digital timing light hooked up and read by my wife which was the same as the tach on the dash. Next weekend I’ll switch back to the 21 inch prop and see. I think the rev limiter on the MEFI 3 is 5200 for this engine but the manual says it’s 4800 rpm.
Some additional mods were a TBI spacer, 10mm spark plug wires and an aftermarket coil with 45000 volts and higher secondary ohms. I also installed another blower motor which sucks air from the outside to the back of the flame arrestor using the same circuit and on and off switch as the regular blower motor. It gets pretty hot in the engine compartment with very little airflow . This I believe helps. Thanks for all your replies and assistance.
The biggest lesson I learned from this crappy design on the cool fuel mercruiser system with ONLY 1 fuel pump ( no low fuel pressure pump) on this first gen cool fuel) is checking fuel pressure in the shop and running the engine without a load on the prop will not give you a correct readout of the fuel psi. It must be checked under load.
But I think I can get more because of the rpm. Right now I max out at 4285 RPM from a digital timing light hooked up and read by my wife which was the same as the tach on the dash. Next weekend I’ll switch back to the 21 inch prop and see. I think the rev limiter on the MEFI 3 is 5200 for this engine but the manual says it’s 4800 rpm.
Some additional mods were a TBI spacer, 10mm spark plug wires and an aftermarket coil with 45000 volts and higher secondary ohms. I also installed another blower motor which sucks air from the outside to the back of the flame arrestor using the same circuit and on and off switch as the regular blower motor. It gets pretty hot in the engine compartment with very little airflow . This I believe helps. Thanks for all your replies and assistance.
The biggest lesson I learned from this crappy design on the cool fuel mercruiser system with ONLY 1 fuel pump ( no low fuel pressure pump) on this first gen cool fuel) is checking fuel pressure in the shop and running the engine without a load on the prop will not give you a correct readout of the fuel psi. It must be checked under load.
