having engine issues.. need a little help, Fuel or ignition. 350 mag mpi

[DirtNasty]

I dont know where the pin connector is, but sure sounds like its running out of fuel to me at the higher RPMs. Id be looking to see what kind of fuel pressure its holding at the higher RPMs. On a 2002 does it have a low pressure pump and a high pressure pump or just the high pressure pump? What I'm thinking is at idle and low RPM it has enough fuel to keep the filters full and pressured, the at the high RPMs the pump isnt keeping up, sucking the filters dry, and then loosing power. Then once it drops back down the pump has enough time to catch back up. Ive seen this happen on other motors. Swapped out pumps and never had the issue again. But a $30 fuel pressure gage is cheaper to try first vs buying a $300 pump.

I agree. anybody have a link to a fuel pressure gauge that will work? I'm pretty sure that it is the fuel. I ran this boat all last summer without one single issue. put it up and didnt winterize fuel and ran bad fuel through it and have had problems since i got it out. I just dont see ignition goin bad like that. not sayin its not possible but..

[Ewok]

I would guess its a fuel pump issue. If you can get your hands on a fuel pressure gauge, hook it up to the fuel rail and run the boat at the higher RPMs and see if fuel pressure drops off at that point. Some of the real mechanics may chime in here and be able to tell if it's the high or low pressure pump but that's what I would check next. If that's not the cause then I would turn to the computer and read the codes and see what could be tripping the ECU into limp home mode.

[IDBoating]

x10 on it being a fuel delivery issue. I bet if you run it on the trailer, it revs high just fine with no problems... which is the litmus test for fuel delivery problems, since it takes very little flow to rev an engine with no load (i.e. prop out of the water). Might be a worthwhile test just to confirm.

Harbor Freight carries an inexpensive fuel pressure gauge. I have one for exactly this sort of test.

[DirtNasty]

well after looking into fuel pressure gauge parts... I went ahead and ordered a fuel pump. It was 90 bucks on amazon... the pressure testing kits were 50 and up. So i opted to pay 40 more and go ahead and get it coming and save time in the long run. also have a anti siphon valve coming even though I think mines fine. I bought the (boost) pump which is the one mounted by the water sep filter. I believe there is another one on the cool fuel section. at least the parts diagram shows one that goes up into the fuel cooler manifold. hope its not that one that is bad. I will check when I get home and see if there is two

[boatwakes]

The DLC is the flat 4 pin connector at the front that says "Transducer"/"diagnostics" on the tag. YOU DO NOT NEED A COMPUTER TO TIME THIS ENGINE the ECM takes care of everything because of the crank position sensor. However, if the timing is off either retarded too far or advanced too far, it will run like poo poo above about 2400rpm (in neutral, no load) but be fine below that. If you adjust the timing and then can get the desired 3000-3500rpm to confirm the timing is correct, then you're done. If it doesn't change then adjust the other direction and check again. If there still is no change then we'll start talking about fuel and pumps.

[DirtNasty]

yes im pretty sure its in time... I went ahead and hooked up timing light and it was around 8 degrees at idle of 600 rpm. Moved the the distributor both ways and it never changed a bit. It revs up just fine and will get to max rpm under load fine as well just loses power after running there for a few seconds. Im pretty sure the issue is fuel...as I was in the beginning. Now just what part... lol that is the question. boost pump should be here soon.

[boatwakes]

Glad to hear about the timing. Again, the computer takes care of everything as long as the distributor is mechanically timed within about a 30* range. Boost pump failures cause a surging symptom above about 2800rpm, the engine will surge between 3000 and 2600 or so. Anti-siphon sounds likely especially since you had crappy gas. To rule out fuel pump(s) use a small outboard style fuel tank connected to the fuel filter and see if the symptoms resolve. If so, it's most likely the anti-siphon. Keep us posted.

[DirtNasty]

Update. So I made a few mistakes wording some of my other posts. I did not buy the boost pump I bought the high pressure pump that is located on the cool fuel system. Not the boost pump near the water sep filter. Anyway. Took it out today after installing new pump and same system. Beyond frustrated right now. No only the engine issues but have had issues with a guys who is painting my speakers and tower. I guess next I will do is get a fuel pressure gauge tomorrow and take it back out and check it and see if maybe the boost pump is bad.

[DirtNasty]

Also installed new anti siphon valve

[boatwakes]

Also something I forgot to mention before, those distributor caps are referred to as "crab caps" from the wire orientation and have had internal cracking problems due to heat. Change the cap and rotor and try again.

[whitlock87]

I had the exact same issue on my Marine power engine and my problem tuned out to be a lose wire going to the high pressure fuel pump ( the marine power engines have two fuel pumps in line with each other. One draws from the tank and the other pressurize the fuel injectors)

[DirtNasty]

well took the boat out today with the fuel pressure gauge hooked up and sure enough im losing fuel pressure after a run at high rpm. I am ordering a boost pump (low pressure) that should fix it.

[IDBoating]

Seems a high pressure fuel pump problem could cause that too, by not being able to keep up with demand on the fuel rail. The more demand from the injectors, the more flow at pressure is required, and if the HPFP can't keep up you'd get exactly this symptom.

I mention this because I am in the middle of helping a friend solve this EXACT problem, and tests show the LPFP is working perfectly with plenty of flow. In his case the effect is most dramatic when hitting maximum acceleration, i.e. trying to pull up a skier from a full stop to ~30MPH. If you accelerate slowly the boat will hit and hold 30 MPH while a HP fuel gauge shows steady pressure, but hit it hard - which requires maximum fuel flow - and the engine sputters and coughs while a HP fuel gauge shows pressure dropping.

In his case the HPFP is driven by the ECU, and its drive circuit isn't pulling the ground side down as far as the manual says it should (likely that the ECU driver is starting to fail). That means the HPFP isn't seeing the voltage it should. We've crafted up an external drive circuit controlled by the ECU which guarantees the pump motor will see full voltage, and the next test drive will reveal if he's done or if a HPFP is needed.

Moral of the story: It may still be the HPFP.

[boatwakes]

For all who have the boost pump and high pressure pump set up: when the boost pump fails, the engine will surge between 2600-3000rpm. When the high pressure fails, the rail will lose pressure and the engine will lose power but not surge.

[DirtNasty]

went with an airtex pump low pressure. runs like a top.