2003 5.0 MPI problems

[Last Dollar]

Had intermittent problems on water yesterday. Boat ran good the day before but after taking a short run up the lake and returning to the dock to wait for guests I experienced a problem getting the engine to run. It would start up immediately but run very rough and would not take the gas when pushing up the throttle. It acted like it was starving for fuel. It would barely run. If I pulled it back to idle it would barely run for a while then stall. It would restart easily but would not rev up or idle. Eventually it seemed to correct itself and ran ok so we headed out. That afternoon after sitting for a couple of hours it did it again exactly as before. I tried positioning the throttle to a very fast idle and cranked the engine only to experience the same thing. After a while of messing with it eventually it seemed to correct itself and run ok. I have it now at home and hooked a fuel pressure gauge to the rail and it reads 35lbs consistently. Of course it has run great on the water hose as I have repeatedly cranked it up, let it come up to temperature then shut it off and sit for a while. I has not had any problems all day. Is there a sensor or some device on these MPI engines that I need to replace?? In previous years I have experienced IAC valve issues and replaced it. I actually carry a spare. But this does not act like an IAC. It acts like fuel pressure or something. Any help appreciated!!

 

[Scott Danforth]

35 psi is low

 

[Last Dollar]

What should the pressure be then??

 

[Scott06]

What should the pressure be then??

I believe 43 psi or so would suspect possible pump or fuel pressure regulator issues

 

[Fun Times]

Alpha or Bravo stern drive?

Was it humid or wet that day or recently? If yes inspect the inner side of the distributor cap for being wet and if not you should still check the cap over for carbon type burn tracks between coil wire input to other cylinder out puts especially if it’s the flat cap which I believe it should be.

Your Engine serial number is?

Pull the vacuum line off the fuel regulator while engine is running to see if the fuel psi goes up/moves about 5ish psi as it should.

 

[Last Dollar]

Alpha or Bravo stern drive?

Was it humid or wet that day or recently? If yes inspect the inner side of the distributor cap for being wet and if not you should still check the cap over for carbon type burn tracks between coil wire input to other cylinder out puts especially if it’s the flat cap which I believe it should be.

Your Engine serial number is?

Pull the vacuum line off the fuel regulator while engine is running to see if the fuel psi goes up/moves about 5ish psi as it should.

This is an Alpha Drive 2003 model. Engine serial number is OM626769. When looking at online parts diagrams it shows two fuel pressure regulators. One is inside the cover on the port side of the engine close to the pump. The other is located on top of the engine on the intake manifold. Both of these regulators are not cheap! Hate to start throwing parts at this trouble. Today I will pull the vacuum line off and check as you suggest. This problem is intermittent but always after it has warmed up and then sits for a while. I will also check the distributor cap although it was not a wet day, but possibly humid. It was 90 degrees In Kentucky Monday.

 

[Fun Times]

The main regulator that controls fuel pressure is the one down low at the pump… Very rare for the one on the fuel rail to exhibit issues but not impossible either… The rail one is more used as an fuel pressure damper for the injectors… unless the distributor assembly housing has already been changed under warranty, the distributor assembly is susceptible to condensation is one reason I mention it for your year model.

Looking for 43 psi too.

 

[Stinnett21]

Replace distributer cap as mentioned. It's easy. Replace IAC muffler, the small piece of foam (white when new, may be black if old) under the flame arrestor. May not be your issue but these are easy tune ups that you can eliminate. FWIW part #2 (check valve assembly) in the drawing for your engine gave me similar fits with my 2002 5.0 MPI. There is a check valve inside that piece that had fallen apart and was allowing hot engine water to back up into the fuel cooler causing vapor lock. Again may not be your issue as your symptoms are somewhat different but as you state this did occur during hot weather as did mine.

 

[QBhoy]

Almost certainly the diz cap and/or fuel quality.

 

[Last Dollar]

Update on my problem. I bought a fuel pressure test gauge and hooked it to the port on the engine. Fuel pressure initializes to a little over 40 lbs and then drops back to 35. Engine running it holds around 33 lbs. This problem has not shown up again since that one day on the first weekend out for the season. I shall keep the test gauge in the boat so if it does happen I can test pressure immediately. It ran fine all day this past weekend. We ran 54 miles on the river with repeated stops and restarts all day with no issues. All hot restarts were very good. Engine had plenty of smooth power while underway.

 

[Scott Danforth]

Update on my problem. I bought a fuel pressure test gauge and hooked it to the port on the engine. Fuel pressure initializes to a little over 40 lbs and then drops back to 35. Engine running it holds around 33 lbs.

you are 10 psi low