Replacing fuel injectors --Help

S

SeaRenity

Member
Mar 31, 2008
200
chesapeake bay / Back river
Boat Info
320 Sundancer 2005
Engines
350 Mag hor.
I am planning on replacing my fuel injectors on my starboard engine this spring. I have been reading up on the process and I am confident I will be able to so the job. Any tips or concerns I should be aware of? As you can see, I have a 2005 350 Mag horizon engine. I'm a bit concerned about relieving fuel pressure -- any suggestions??
Anyone take on this job that can give me guidance?
Thanks so much
Rich
 
If it's been sitting for a while, there won't be much pressure. But you can relieve and hold a rag over the fitting as a precaution. BUT... why replace? Why not get them cleaned and rebuilt for about $20/per?
 
scoflaw said:
Why do you think you need injectors ?
Click to expand...

8 years ago I replaced port engine CF3 unit and have had no problems with this engine. For the last 1 1/2 years or so the starboard engine (original CF3) has required more throttle to get to equal RPM as port, it also uses more fuel than port (documented). My belief is the first few injectors in the rail are partially clogged with black paint from CF3. This is my best guess--I am looking for help here from anyone ???

Also can anyone help me with suggestions on replacing injectors --- Tough job? should not be attempted by knowledgeable DIY er.
Please offer up some help

Thanks
Rich
 
Have you repaired/cleaned the rest of the fuel system so the injectors don't get clogged again ?
 
Definitely check things, first. Fuel pressure.. fuel pressure regulator.

Side note... I'm sure 8 years ago you had the work done under Merc's goodwill warranty (or an original extended warranty if you had it). BUT... in many cases, Merc is STILL covering this work. Talk to a good Merc dealer about it.

Rebuilt is as good as, or better, than new.
 
I am also considering pulling my injectors for cleaning or replacing for the same reasons. I would answer your question if I knew.

Maybe someone who has removed / replaced injectors on these motors will chime in.
 
Chime.
I have done this a couple of times. to release fuel pressure, screw on a fuel pressure gauge with release tube to the schrader fitting at the front of the intake manifold. It has a cap on it, and is like a bicycle tire valve. you can release the pressure and subsequent gas with the drain tube. This is a handy tool to have for fuel rail troubleshooting anyways.

There are a couple of things you REALLY need to pay attention to.
1. The electrical connectors to the injectors have a wire around the base that at first blush looks like you would pull it out to release the connector. Not so. You push it in. The connectors are a weak point of the injector. Rock it too much and you will crack or even break off the connector. If that happens, throw it away. I lived through years of intermittent performance on my port engine after an angry mechanic changed the engine out for the 3rd time before I got the boat.
2. The fuel rail, and injectors have a very specific way of coming out, and going back in. You don't just yank it up and out. You have to start from the front, and gently rock and pry it up, leaving one side of the rail's injectors in the block, and one side of injectors in the rail. Installation is the opposite procedure. I suggest you get the service manual for that engine if you don't already have it, and read the procedure about 10 times before attempting. When replacing the rail, be very careful not to pinch the o-rings on either end of the injectors. This is a very tight fit, for good reason.

Good luck. I'm about to do it again on a repower engine, which unfortunately the PO used sealant instead of a gasket set to re-seat the plenum, so I'll be using the old piano wire trick to cut around the four throats so i can get to the rail. When you do yours, replace the plenum gaskets. Don't do what this guy did. If you hunt around You Tube, you will find some examples of making injector cleaning devices. Pretty simple to rig up.
 
Thanks so much for your feedback and suggestions.
Few questions, I tried a few auto parts stores including NAPA for the fuel pressure gauge -- where and which one have you used.
Also, you mention rocking the fuel rail -- do you mean you replace injectors in one sise without taking the other side out and than reverse this for the remaining 4?
Where can I get a service manual for this engine??

Thanks so much
Rich
 
SeaRenity said:
OW390584
OW390636
Do you think I need a special tool for removing fuel lines from rail?
Thanks
Click to expand...
looks like its a quick connect fitting.
you will need a quick connect tool remove fuel line.

parts-catalog

Heres mercury parts website you can search for parts and diagrams with your serial numbers.
 
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