5.0 Mercruiser loses power gradually?

Kuneha

Cadet
Joined
May 8, 2016
Messages
22
Hello.

I have a 1999 Regal Commodore 242 fitted with a Mercruiser 5.0 EFI.

The issue is when first setting off, I can get the boat to around 30mph. Then as time goes by, say 10 minutes, it'll top out at 25mph. Skip forward another 10 minutes it'll top out at 20mph and so on. It will get it a point where it won't go beyond 10mph if that at full throttle. The engine just bogs down. With very fast throttle input the engine nearly dies. I have to apply the throttle slowly?

So far under the mechanics advice I have had it serviced (including new rotor arm and distributor cap, antifoul, new fuel pump, new batteries) and yet the issue still persists. They believe it is a fuel issue, perhaps the fuel pressure slowly dies off but the mechanic at this point isn't interested anymore as he can't scam more money out of me for stuff that isn't causing the issue.

What does your experience tell you guys?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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51,478
what is your fuel pressure? when running under load.
 

Kuneha

Cadet
Joined
May 8, 2016
Messages
22
This is something I cannot say as the mechanic had not bothered to check. Would you know how I can check this myself as I wanted to compare pressures at varying times.

Regards.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,478
you need to use a fuel gauge, and screw it into the schroeder valve.
 

alldodge

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Mar 8, 2009
Messages
43,398
Have you changed out the fuel filter?
You should have TBI and will need an adapter to connect inline. Remove the fuel line at the TB and install it. 91-806901

TBI adapter 91-806901.jpg
 
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