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Fluctuating rpm

rmhcpa

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I replaced both elbows and one

I replaced both elbows and one exhaust manifold on one of my 1995 454 CID 7.4L MerCruiser engines. I checked the torque after the engines warmed up to normal operating temperature as well as after a half hour cruise. The next day I ran the boat up to wot. When I reduced speed to 3000 rpm the tach for the engine which I recently worked on began to fluctuate and a tapping can be heard around the replaced manifold. I checked all plug wires but none are loose and there is no leaks on the manifolds or risers. Is this problem related to the new manifold or something totally different?
 
"You may be associating an unr

"You may be associating an unrelated problem to an area you just worked on--I do it all the time!

Suggest you leave the motor sit overnight after a good run, then pull the plugs on that side (ground the ignition) and crank her over. Hold a white paper towel near the plug holes to catch any water (if any) that shoot out.

If you do see some water, remove all of the gaskets from that side and try again.


Jeff

PS: Mercruiser maniflds are notorious for too thin gasket sealing areas. You must do a first class job in that area or water will leak downhill."
 
It is possible your tapping is

It is possible your tapping is actually a ticking. Make sure you did not crack or break a spark plug or cut into a plug wire. If you start your engine in the dark it will be easier to spot a spark leak arcing towards the block.
Dania Marine Corp.
Supplier of marine engines and equipment
954-927-2999
 
"Thanks for your responses. Ye

"Thanks for your responses. Yes, it was actually more of a ticking. It appears the vibration at wot shook one of the plugs loose but not off.
With pliers, I lightly crimped the plug connector for a better connection. Glad it was such a simple problem. Thanks again."
 
"Have a fluctution problem my

"Have a fluctution problem my self on 454 1997 efi merc cruiser engine, after running 40 to 50 min the starboard engine atarts fluctuating like it not getting enough fuel, have replaced the Fuel cooler and both the high and low pressure pumps, change syphon valves,chech fuel vents, check plugs,clean both tanks,are we missing something, I am at my wits end Please Help!!!"
 
I have had that problem on a f

I have had that problem on a few occasions-with 3 different causes. 1. The little cartridge fuel filter at the carb was clogged. 2. Bad fuel pump. 3. The siphon vent on the tank was blocked. A little carb cleaner sprayed into the screen fixed it.
 
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