Loss of Power - 350 MAG MPI

[rphipps]

I have a 2000 21V with 350 MAG MPI MIE. Boat seems to run fine when just cruising with a few people. But once I try to pull tubers or wakeboarders, there's a signficant loss of power on the low end and struggles mightily to get above 15-20 MPH. Fresh gas, changed Cap, Rotor, Plugs & Wires and mixed in SeaFoam. Any help tremendously appreciated!!

[Thegerman618]

Few questions that I am sure will come up from others. Does the engine stall or shut off when it happens? Do you have a speed controller of some kind (make sure its off when running around)? Fuel Filter/water separator change? I had the same engine in my last boat and it did the same thing turned out to be the high pressure fuel pump. Sounds like you have a fuel starvation problem, but it can be narrowed down to 3 things, FUEL, AIR, SPARK. I eliminated spark due to you have already changed the common issues stuff. If you can measure your fuel pressure across the rail, I want to say its supposed to be in the 40PSI range (some correct me on that if I am wrong). Air is pretty simple, most common is the IAC Valve/filter never changed mine, but I know for a fact there is a really good walkthrough on how to do it I think by BoatWakes or Chpthril. Hopefully this helps, that motor is pretty bulletproof. However, I would put good odds on the fuel pump being bad.

[rphipps]

Engine doesn't stall, sputter or shut off thankfully, just really struggles to generate power when taking off under load (i.e. tubing). No speed controller. Water/Fuel separator new this spring but haven't changed fuel filter or checked fuel pressure. Thank you for the input.

[Thegerman618]

the no backfire or sputter is interesting, almost sounds like it could be something simpler. Check your battery cable connections, they may be loose and causing a volt drop under heavy load.

[boatwakes]

Check the electronic connections on each of the injectors. As of late I've run across several injector terminal connections, on the injectors physically, that have broken. Check them all first before performing the next test with the engine running. It's important to become familiar with how to remove the injector harness from the injector and it's very easy to do. Identify the retaining wire of each injector harness connection, it's the small stainless tension wire that spans the width of the connection. To remove the connection, pinch the retaining wire and hold the opposite side of the injector and then rock the connection back and forth. Each harness connection has a removable waterproof gasket tucked inside. They're usually blue and square and EASILY LOST if you're not paying attention so check each connection before replacing the harness.
From your description, you need to check all the injectors while the engine is running IF you don't find any that have broken connections.
The easiest way to do this generally takes two people, one holding the throttle steady at 1200rpm and one disconnecting and reconnecting each injector wire. The purpose is to determine if cutting out an individual cylinder changes the sound and rpm of the motor. Perform the test and get back with your results.

[TeamAllen]

Welcome to the site!! How long have you owned the boat? Do you know what prop is on there?
Post up a pic of that V-drive

[Thegerman618]

I was doing my best boatwakes, glad you chimed in I am fresh out of ideas.

[rphipps]

Thank you - will check connections and perform test today.

[laserfish]

What boatwakes said. I broke the right rear injector changing the impeller a few years back. Visually, you couldn't tell unless you physically wiggled the connection. Then it was obvious something was wrong. Made it run like a dog, just as you describe. Drove me nuts for a time until I discovered it by accident.

[rphipps]

Boatwakes - I finally got back in town and had time to check out your recommendation and it does appear I have one broken connection on an injector. Apologize if this is a dumb question, but safe to assume I'll need to replace the injector? Or is there a way to simply repair the connection? If I have to replace the injector, is that a fairly simple repair? Thanks again for your help.

[boatwakes]

Replace the injector, I wouldn't try to repair it. http://www.fuelinjectorconnection.co...rds%5D=861260t
$100 shipped. Mercruiser part number 861260T.
To replace, follow these instructions:
- depressurize the fuel rail by pressing the needle on the Schraeder valve located at the front of the fuel rail, if nothing comes out the rail is not under pressure.
- remove the 4 7/16" hex head bolts that hold down the fuel rails
- remove the retaining clips from each injector
- take photos of the harness connections to each injector as it's possible to wire them out of sequence and cause the injectors to fire at the incorrect time.
- lift the fuel rail up by rocking back and forth until it pops up free either with the injectors or leaves them in the intake manifold. CAUTION!!!! Fuel will spill out of the rail as soon as the first injector pulls from the rail and you need to have paper towels or rags at hand to catch and clean that up.
- it's important to note you're dealing with an oring seal both top and bottom on the injectors and if any of them get damaged, they will need to be replaced with new or they will leak. The upper oring holds the fuel rail pressure and the lower prevents the manifold from encountering a vacuum leak. The replacement number is available at most auto parts stores ac delco pn 217-3365 or bwd 274572, 8 pack and the total to replace for a set of 8 injectors is 16 orings.
- remove the faulty injector and any others you want to change orings on.
- lubricate the new orings with grease and install on the injectors.
- install all the injectors into the fuel rail and install the retaining clips for each individual injector at this time.
- clean the injector bores in the intake manifold and again grease the lower orings prior to installation.
- set the injectors onto their respective bores in the intake manifold, making sure everything is lined up perfectly straight up and down.
- apply pressure to only one fuel rail until it pops down into position, checking for torn orings or pieces of oring that may have dislodged during installation. If everything looks good, move to the other side and check as well.
- install the hold down bolts with loctite blue on the lower threads of the bolts and tighten to 8-11 ft/lbs.
- once all the electrical is reconnected, pressurize the fuel rail by cycling the key on while the fuel pump primes. Relieve the air pressure in the rail through the Schraeder valve with a rag in hand to clean up any spilled gas.
- if everything looks good and there are no rail leaks, fire it up and check again for leaks. Let it run to temp and keep an eye out for gas leaks. If you find any, repair as required.

You are dealing with a flammable liquid and can hurt yourself and others if you don't follow proper safety procedures. Please be careful and quadruple check for leaks. If you're confident enough to perform this repair you'll also be able to understand the fuel system better, save some money and know that you're not counting on someone else to keep your boat running right.

[rphipps]

Ok, I received the injector today and replaced per your instructions. Knock on wood, everything went together relatively smoothly and she ran great on the first test run (with no fuel leaks). Real test will be this weekend when I have a bunch of kids on the boat and pulling tubes & wakeboards. But for now I'm cautiously optimistic this has done the trick. Can't thank you all enough for the assistance - plus I've learned a lot during the process.

[rphipps]

Unfortunately replacing the fuel injector with the broken connector didn't solve the problem. So I took the next step and drove the boat at 1200 RPMs and disconnected each injector one at a time. We did not notice any change whatsoever in speed/rpms/sound, etc. Is that the expected outcome? I also tried running another can of SeaFoam thru the system and that didn't help either. Any suggestions what I should check next?

[Thegerman618]

I am back to fuel pump, mine did this the last weekend I owned my previous boat (Centurion but same engine) traded the boat in, they called me out and showed me the pressure on the fuel rail at idle was pretty low. Under no load it would rev and do everything fine, but load it down with people and ballast and about 1500 RPM it would backfire one good time and would not plain out had to limp it home. Dealer knocked $400 of my trade to replace it. I didn't care I was buying a Tige'

[rphipps]

I'm pretty inexperienced at this stuff (but learning more & more on a daily basis); I noticed your earlier post referenced a high pressure fuel pump. Should I assume by that statement there's also a low pressure fuel pump? If so, do I need to worry about that pump or is it safe to assume the problem would likely lie with the high pressure pump? And is there any way to test the pump, or do I pretty much just need to order a new one and install it? Thanks as always for your guys' help - it's very helpful and much appreciated.