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57 not reaching RPM WOT

R

roxy

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"I have twin 5.7 GI engines in

"I have twin 5.7 GI engines in my boat. One engine will reach 4200+ RPM but the other will only reach 3400 RPM under way. When I push the throttle down it reaches the 3400 RPM point at about half way the same as the other engine but I get no additinal RPM from there.
If I rev the engine no load it runs up over 4000+ no problem.

I have checked the injectors at the dock and they seem to be working. With the throttle wide open the butterfly in the TBI is wide open as well.

I have replaced the fuel filters and even ran off the other tank to verify no fuel line restriction.
Spark arrestor is clean.
Plugs, cap, wires are only a year old.
Whats next??? Any ideas??

Weak fuel pump??"
 
"I do not advise exceeding 250

"I do not advise exceeding 2500 rpm on an engine without load.

Did this problem develop 'overnight'?

I would start by pulling a few plugs and checking their condition. Also ensure the cap and rotor are in good shape (wear can occur within one year). Is the engine timed properly? Start with the basics on an EFI system. If they check out then begin looking at the EFI components.

Does the engine idle well? How does it run at 3400 rpm? When you increase the throttle to WOT does the engine surge, or run rough? You may have a faulty TPS, but I would rule out the items mentioned above first."
 
"Mike
I have not had the boat

"Mike
I have not had the boat off the dock in a couple of weeks and never run it over 3400 rpm so it is hard to tell when it started. My other engine had a bad t stat so I wanted to push it a little bit more than normal after changing it to check things out and thats when I noticed it. The engine starts great, (about 1 turn and she is running)runs great, sounds great. When I do get to the 3400 range it then sounds like it is starving for air. It never surges or runs rough at all. I will pull the plugs cap and rotor and check them. I am going to swap the coil as well. I read a weak coil could cause this problem. I did see the injectors have a small filter in them. May be worth a look as well. The way it starts and runs the timing seems correct."
 
"I have an identical issue, bu

"I have an identical issue, but it is with an 8.1Gxi. Port engine goes as high as I like but the starboard peaks at 3000. I will go through the recommended steps tomorrow as listed below and report back. Hopefully, we can all keep this thread going though resolution."
 
"Ok, Call me a dope.
After d

"Ok, Call me a dope.
After doing all the checks listed above including a tune up nothing changed in my test run. I came back to the dock and decided to check the props/outdrive for possible restrictions. I raised both drives and what I saw was a shock. The engine/drive easily reaching RPM was missing the rear prop of the duo prop system. I was running on one prop on that engine/drive while the engine that I thought was having problems was working fine all along. My drives are hidden by a swim platform and are difficult to see. (my excuse and I'm sticking to it)

I checked some other sites and found out other boaters have had the same thing happen. The duo props need to be checked for tightness very often. A poor locking system in the cone nut and cone bolt is the probable cause."
 
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