lean engine problem

[infotom]

I have a 01 21v 350 mag mpi horizon, I ran it for the first time this season, it starts ,runs then goes lean and stalls. I can spray carb cleaner in the throttle body and keep it running. it will accelerate if I feather the throttle. it only has 25psi of fuel pressure. I replaced the filter, pump and blew out all the lines,checked the screen at the regulator. all is clear and still no go. I'm thinking I have to plug into see what the sensors are doing, but i don't think that that can control my pressure. Any thoughts would be appreciated.

thanks

[chpthril]

I have a 01 21v 350 mag mpi horizon, I ran it for the first time this season, it starts ,runs then goes lean and stalls. I can spray carb cleaner in the throttle body and keep it running. it will accelerate if I feather the throttle. it only has 25psi of fuel pressure. I replaced the filter, pump and blew out all the lines, checked the screen at the regulator. all is clear and still no go. I'm thinking I have to plug into see what the sensors are doing, but i don't think that that can control my pressure. Any thoughts would be appreciated.

thanks

Fuel pressure regulator will control the fuel pressure. Can you slowly pinch off the return line and get near the correct pressure? Not sure if your year boat has 2 pumps or not, if so, one might be faulty.

Look for a kink or collapsed feed line between the tank and engine. May need to pull the pick up out of the tank an inspect for restriction.

[brody66]

It sounds like you already replaced a fuel pump but i would replace the regulator first, they are usually pretty reasonable, they are like 50 bucks for a chevy half-ton, but then again when are marine parts not two to three times more.

[infotom]

I just pulled and blew through the feed line from the tank to the filter. It is clear. I have only one pump at the block with a cooler. key on engine off 25psi, engine running 25psi, pinch off the return line 25psi(running), remove the vacuum line to the regulator running no change. the reguator holds vacuum, unless it is just stuck.Some of the local boat shops say regulators don't go bad.What is the 3-wire sensor for in the fuel rail?

Thanks

[chpthril]

With the return line pinched off (dead head the pump) the pressure should have jumped to 60+. Bad fuel pump or the pick up is drawing air. Check voltage at pump while running by jumping across the pumps power and ground.

3 wire sensor may be fuel temp sensor.

[dmtvm]

pressure

25 psi sounds low. I thought the MPI needed more like 40psi. Do you have the exact specification for your fuel pump and engine model?

[R&T Babich]

Our boat has 25-26 psi fuel pressure with key ON, engine OFF. I'm not sure what it is while running, but I thought it was around 32-35 psi. I'm going out next weekend and will check and add it to my notes taped to the engine cover. The sensor on ours is near the inside end of the left rail (engine orientation) and is for fuel pressure. That is the sensor that set off dogbert's engine warning system beeper when the pressure regulator was keeping the pressure too low at high demand. It has 3 wires - black,green,white which go directly to the ECU. I think it is Merc part no. 710-881879A-8, but it is not listed in any Merc diagrams for our engines that I have found.

Don't forget about the anti-siphon valve (1/4” NPT x 3/8” hose barb, Tempo 260030) fuel tank fitting. The fitting in the fuel tank has an anti-siphon ball valve in it. If it is stuck it can cut off full flow entirely or maybe just enough to limit fuel flow.