Ajay (and forum members) -
Thought that I would share a similar issue that I had with my 1999 350 MAG MPI as this sounds somewhat familiar to an issue I had this summer. Was able to diagnose and fix (if you don't want the full story - see below).
Issue: Initially - Intermittent loss of power. Finally - Died and would not re-start. Fuel pressure and supply both good. Spark – intermittent/weirdness.
Issue started last Fall. Just cruising and start to feel like the boat was running out of gas; power would momentarily fall off (like no power; ignition shut off), then would come back. Ran absolutely fine and all engine RPMs, even WOT (hits 4200-4400 at 60MPH). Put it away for the winter after winterizing; seem to run fine on final run on the hose before putting away for 6 months.
Pulled it out this spring and it gave me a little grief on starting; different than the past 9 seasons - cranked, tried to start. Cranked, tried to start, then caught and run okay on the hose. I changed the drive and engine oil in the fall, and re-rebuilt the raw water pump (impeller+housing). Replaced the Dist. cap and rotor+Ign trigger. Final run on the hose - perfect. All is good; off to the lake for a camping weekend with the family.
In the water, I did a couple hot-laps to make sure that it was good before picking up the wife and headed out for a day on the lake. About 10min into our trip, started to feel the 'loss of power' again - very very subtle, but I decided to turn around to just make sure all was good. Another 10 min, heading back, and it was bucking; like ignition was being turned on and off. Made it to the no wake zone and it died - would crank and crank, but would not catch. Another note; fuel pump would run intermittently with ignition on, engine not running; like there was a loose connection (Note; this is not the normal start up, which is to run for 3 seconds on contact, prior to starting). Three day weekend on the Lake ended in 20min. Fun, I love boating!
So, did the usual checks; fuel and spark.
Fuel: I have a pressure gauge right on my fuel rail (STBD side, opposite schrader valve) - Shows 35-38psi (good) when the fuel pump runs. As noted above, the fuel pump would start/stop intermittently like there was a loose connection. Pulled all the connectors off the relays and checked all (three) fuses, plus bus under the dash - all good; very good. Pulled the Fuel filter and it immediately spewed fuel; so it was not sucking air off the bottom of the filter (have had that issue too in the past - arrrgh).
Spark: Weird. When cranking, there was no spark - none. But, then the ignition was turned on, I would get a spark about 50% of the time with initial contact. Thinking that the coil was going bad – meanwhile the fuel pump seems to have a mind of its own; just taunting me further and driving me to obsess on fixing this issue.
So, comes down to a couple things at this point. Coil or something’s up with the ECM. Coil issue – that would be great. ECM issue – time to sell the boat? In the final throws of my patience, I pulled the coil off and did some checks; Good continuity between both sides; 12v and HV. Noticed that it was leaking oil – thinking that it was a temperature issue, but then again, it did not start hot or cold. Pulled the distributor cap and all my new parts looked good; nothing out of place. Inspected the ignition senor with a flashlight and was not impressed – looked pretty bad; little ‘rusty’ on hardware, and was blown away that the circuit board/solder joints were all exposed..
Diagnosis and Fix. Ordered new Coil and Ign sensor assy.
Installed the coil first, same issue; weird cycling of fuel pump – engine would not start.
Installed the Ignition sensor, noting that new assy is a much better design; fully encapsulated with epoxy, and now includes a grounding wire. On first attempt to start the engine may have made it a full rev before it caught and ran like a champ.
Ajay – if your running on your original ign. sensor, you may want to just replace it. So worth the $65 in my book.
