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2002 sea Ray 8.1

RonR

New member
I have an 8.1 mercruiser in a 360 and it run smooth up to 4000 rpm and then starts to surge...42-4400 rpm back to3900 and back and forth. After removing the vent for the gas tank it ran for a while and then started pulsing again.... Then after removing the gas cap while at wot ,the engine ran perfectly......we ran for an hour at 3400 rpm without any problems....after that we ran the motors for 3 hrs to travel down the lake....again after trying to go to wot , the motor started to pulse and surge again.......I have twice changed fuel separators and put in new plugs....any suggestions ???????? We had the motor scanned,but no problem codes came up....
 
Ok, we put a pressure gauge on the fuel line and at first pressure was 36, then as we accelerated the pressure fluxuated from 30 down to 20 and back to 35 but never went back into the 40's. Went back to idle, accelerated slowly, the pressure stayed at 40 until we get to about 3200 rpm then ,the pressure starts fluxuating, engine goes into guardian and we have to back out of it ???????
 
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How do we check the low pressure pump....is it the small pump on the tank..and use the same pressure gauge????? Thank you RR
 
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I would start buy checking for a fuel restriction. Start at the fuel tank. Pull the dip tube assembly and look for a blockage. Pull the fuel shut off solenoid and do the same. Follow the fuel line all the way to the engine and see if you have an inline strainer. Look at the attached photo.





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I'd also add to Chris' list these:

* Anti-syphon valve corrode/not fully opening?
* shutoff valves not fully open?
* spin on filters not seated tight?
* hose clamp loose?

An air leak on the suction side is just as bad as a restriction in terms of impacting the fuel pump...
 
We don,t seem to find any restrictions on the fuel side ,either at the tank,or at the pump......was informed this has a pancake filter under the water seperator.....how do I access it.......its the only fuel thing left!!!!!
 
With only 20-30psi on the high side pump...should I replace it???? I don'T want to start changing things and not solve the problem
 
Are you still having problems with fuel filler cap off? Having things run OK after removing fuel filler cap usually points to a blocked fuel tank vent line.
 
Are you still having problems with fuel filler cap off? Having things run OK after removing fuel filler cap usually points to a blocked fuel tank vent line.
After running the boat for a few hour ride the engine started acting up again.....removing the gas cap didn't seem to have any affect on it!!!!!!! Before we left for the trip.....pulling the gas cap let the engine run just fine..... We thought we had cleared the gas vent line?.....?
 
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