1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electric?

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kb3bfy

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All:

I have a 1989 Mercruiser 454 big block in a 34 SeaRay.

This season, I have been having issues with the port engine. While running at idle it sounds great / no issues with it knocking out or acting up when you shift; it fires right off as well when you hit the key.

However, when you accelerate to 1300 - 1400 RPM, the engine will run fine and then intermittently act up (acts like it looses power); I loose roughly 50 - 60RPM for say, 6 seconds and then it goes back to normal for 5 - 10min before acting up again. If I pull the throttle down, everything goes back to normal with no issues...

Additionally, the engine does not want to open up without loosing power as mentioned above.

So far, I have replaced all wires, distributor cap / rotor (plugs are next weekend) as well as the ignition coil.

Any thoughts or input would be appreciated.
 

Grub54891

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Re: 1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electr

Couple questions come to mind,are you running from seperate fuel tank's? Could be a water in fuel issue,if same tank not so much.Could be a carb needs rebuild also.. Start with replacing all fuel filters,even water seperating filters will let water in if there is to much. Fuel pump bad? Restriction in anti syphon valve? Ok,are you running piont's? You replaced everything else so I have to assume it's electronic.If points,replace em. Check timing also. However I've seen the weights/springs below the distributer plate (if it has them) wear out too.
Hop this helps,mabe I missed something and someone else will correct me.
Grub
 

kb3bfy

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Re: 1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electr

Thanks for your thoughts; this has been perplexing...I have been trying to determine if it is fuel / electrical...

I am running on the same tank and the other engine runs great. Additionally, I have purchased a new Sierra Fuel pump that I plan to install next weekend along with new spark plugs, so we will see if that fixes anything. If not, perhaps the carb?
 

kb3bfy

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Re: 1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electr

I just forgot, no points.
 

Grub54891

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Re: 1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electr

Replace filters,fuel pump,test run,then move to a carb rebuild if it still acts up.
 

Bt Doctur

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Re: 1989 Mercruiser 454 7.4L Big Block: Intermittent Issues / Will Not Open Up-Electr

anti-syphon valve sticking partially closed or fuel tank vent clogged a bit.Wasps love that area, so do spiders.
 

RickBotts

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I am having the same issues with my port engine. Same motors and same year. I have replaced the coil, distributor cap, rotor, plugs, fuel filters and the wires are coming. I had the fuel filler hose replaced and when it was done by the tech it was raining. I was wondering if fuel got into my port tank but wouldn't of changing the fuel filters stopped that?
 
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