No power after half throttle on port motor. Mercury horizon 2001

Throttling up in neutral means nothing - forget about that tidbit of info - get it outta 'yer head.

Replacing injectors 'just because' is also a bad idea - forget that one, too - at least for the time being. Besides, they can be tested and rebuilt. Why would you replace something without knowing if it's bad?

As mentioned, start with pressure testing under load. Heck, you can start with it in neutral since if it's low then, it will definitely be low under load and no reason to take it out on the water. But first see if you've got the proper pressure getting to the injectors.

You need to figure out the general area that is causing problems - then you can start narrowing it down. Diagnose - don't just replace. If you're not comfortable with this, then hire a good mechanic. It may be worth a few hours of labor paid to a pro at this point so you can't get things figured out and start enjoying the boat.

Also make sure your cap/rotor/wires are good... and make sure the wires are going to the correct plugs.
 
DarrenC said:
The water Separator filter was changed last year and this year. We did a fuel compression test at the rail and if I remember correctly it was going up to 20 psi that it wasn’t holding it was dropping to zero so we changed the fuel pump. The fuel pressure had remain the same and was told by another mechanic that the fuel pressure was good. When you say Testing under load do you mean checking fuel pressure while the boat is Under way? Is there a way to check the fuel injectors?
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As Lazy Daze stated, diagnose first before changing out parts. I noticed in your post quoted above that you did have the fuel pressure checked, however 20 PSI seems low, since the regulator for your engines should have a pink dot which is, if I recall, about 30 PSI. I believe that disconnecting the vacuum line to the regulator causes it to raise pressure to it's max. Fuel pressure at the rail can also drop if an injector is stuck open. Sticky injectors can also be intermittent; they can be stuck open or closed, or somewhere in between. Also, don't forget about the tiny screen filter in the regulator. If you are getting low fuel pressure under load, this could be clogged up with debris.

Good advise on spark plug wires, etc. Some plug wires are notoriously difficult to snap on properly. Confirm that all are properly making contact.
 
amajamar said:
As Lazy Daze stated, diagnose first before changing out parts. I noticed in your post quoted above that you did have the fuel pressure checked, however 20 PSI seems low, since the regulator for your engines should have a pink dot which is, if I recall, about 30 PSI. I believe that disconnecting the vacuum line to the regulator causes it to raise pressure to it's max. Fuel pressure at the rail can also drop if an injector is stuck open. Sticky injectors can also be intermittent; they can be stuck open or closed, or somewhere in between. Also, don't forget about the tiny screen filter in the regulator. If you are getting low fuel pressure under load, this could be clogged up with debris.

Good advise on spark plug wires, etc. Some plug wires are notoriously difficult to snap on properly. Confirm that all are properly making contact.
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Thanks for your response. I put a new regulator and screen when I had new fuel pump and assembly installed last year. I’m going to be changing out the injectors this week and I will check all the plug wires while I’m there again. Can anyone offer any tips on installing new injectors? Should I lubricate them with anything special? Should both o rings be lubricated?
 
amajamar said:
As Lazy Daze stated, diagnose first before changing out parts. I noticed in your post quoted above that you did have the fuel pressure checked, however 20 PSI seems low, since the regulator for your engines should have a pink dot which is, if I recall, about 30 PSI. I believe that disconnecting the vacuum line to the regulator causes it to raise pressure to it's max. Fuel pressure at the rail can also drop if an injector is stuck open. Sticky injectors can also be intermittent; they can be stuck open or closed, or somewhere in between. Also, don't forget about the tiny screen filter in the regulator. If you are getting low fuel pressure under load, this could be clogged up with debris.

Good advise on spark plug wires, etc. Some plug wires are notoriously difficult to snap on properly. Confirm that all are properly making contact.
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Problem is I’ve had 2 mechanics working on it and have a list of things as you can see in post that we’ve done. I even had a friend that is a mechanic look at it this week and while he was pulling the plug off the injectors he snapped 2 of the heads off the injectors so now I’m already forced to replace 2. I’m not going to give in until I find it.. I’m valuing everyone’s advice and sincerely appreciate the help. Wish I could hire one of you to fix it. I have a fuel pressure gauge once I fix the injectors I will be checking fuel pressure. As one of you stated it should be at 30 psi. And when I shut switch off should it hold at 30 psi??? If so I recall it only went to 20 psi and switch off and wouldn’t hold is reason why we replaced a very expensive fuel pump.
 
Use some grease on the o rings. Yup, old plastic injectors do get brittle. Should hold pressure for a reasonable length of time.
 
scoflaw said:
Use some grease on the o rings. Yup, old plastic injectors do get brittle. Should hold pressure for a reasonable length of time.
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Any kind of grease? I’m asking for when I install the new ones do I use grease? Or Vaseline?
 
Unbolt the rail and they pull out. Need to be careful on install so you don't pinch an o ring
 
scoflaw said:
Unbolt the rail and they pull out. Need to be careful on install so you don't pinch an o ring
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Thank you.. just saw you live in the cape.. my boat is in Fairhaven in Fairhaven New Bedford Harbor. Hoping to get this up and running soon.
 
DarrenC said:
this is now the second season with no answers yet. My port motor gets up to 3.9 at half throttle and same with starboard motor. When I give more throttle starboard motor goes up over 5.5 rpm giving outstanding power and port motor gives nothing more. After a while it will increase slightly as it’s working off the other motor it seems. Things I’ve done so far. Checked timing by a professional, replaced fuel pump. Checked all cylinders doing a compression test and fantastic compression. She throttles up in neutral no problem it’s when it’s under way. Would anyone have any idea what it could be the restriction? I’ve even took off props and sent them out to be checked and cleaned and tuned up, could it be a fuel restriction? Any help from anyone that had this in the past would be sincerely appreciated. I’m racking my brain. Thanks
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Here is your. answer..... you have one to more bad spark plugs on that engine. The plugs may look ok, but replace and enjoy!
 
ojet said:
Here is your. answer..... you have one to more bad spark plugs on that engine. The plugs may look ok, but replace and enjoy!
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Thanks. I replaced all the fuel injectors today going to test it tomorrow if it’s not any better I’m going to do new plugs and wires. I keep you posted. Thanks
 
DarrenC said:
Thanks. I replaced all the fuel injectors today going to test it tomorrow if it’s not any better I’m going to do new plugs and wires. I keep you posted. Thanks
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It won't be better until you change the spark plugs on that engine.... Spark plugs are cheap and easy to replace.......you will not be disappointed!!!!
 
Here is a update. I changed all 8 injectors yesterday took me close to 4 hours. Not a hard job just time consuming. Took it for a test ride today and thank God it’s fixed... the rpm go to 4.5 on it own right away and keeps up with other motor. It ran very smooth. The old injectors were a mess.. I’m still going to replace the distributor cap plugs and wires. I’m having a little trouble locating the parts online my serial # is OL670519. 350 mercruiser Horizons MPI. Looking for plug wires and distributor cap. Thank you all very much for your assistance and help. I sincerely appreciate it.
 
DarrenC said:
Here is a update. I changed all 8 injectors yesterday took me close to 4 hours. Not a hard job just time consuming. Took it for a test ride today and thank God it’s fixed... the rpm go to 4.5 on it own right away and keeps up with other motor. It ran very smooth. The old injectors were a mess.. I’m still going to replace the distributor cap plugs and wires. I’m having a little trouble locating the parts online my serial # is OL670519. 350 mercruiser Horizons MPI. Looking for plug wires and distributor cap. Thank you all very much for your assistance and help. I sincerely appreciate it.
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Awesome to hear that!
 
DarrenC said:
Here is a update. I changed all 8 injectors yesterday took me close to 4 hours. Not a hard job just time consuming. Took it for a test ride today and thank God it’s fixed... the rpm go to 4.5 on it own right away and keeps up with other motor. It ran very smooth. The old injectors were a mess.. I’m still going to replace the distributor cap plugs and wires. I’m having a little trouble locating the parts online my serial # is OL670519. 350 mercruiser Horizons MPI. Looking for plug wires and distributor cap. Thank you all very much for your assistance and help. I sincerely appreciate it.
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If you can't find the parts start with the link below. I put your serial number in and you can get all the numbers and buy from them or search elsewhere online
http://www.marineengine.com/parts/mercury_marine_parts/sn/0L670519/3F494AJM1/4835_100
 
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