8.1 GI low rpm

2004 four winns 8.1 volvo with 90 hours. We had a problem with the starter and a mechanic replaced it. We took the boat out and it fired up great took a little bit to get up to 150 degrees but never did get to 175. Not the highest rpm is 3600 and takeoff seems slower than before. Max speed is in the 40's with the 34-3600 rpm. I changed fuel filter and still does the same. The gas is down to 1/4 tank and nothing else has really changed. Idle is good and smooth I have not tried to rev the engine in nuetral. Is there a switch or something that might have been hit when replacing the starter that would cause this and what should the volt meter read when running. Volt meter reads 13 and a shade under on the dash. What is the best way to hook a volt meter to see the actual charge volts? Also cleaned the screen for the air intake.

Re: 8.1 GI low rpm

Have you checked the spark plugs and each plug wire for spark? With 8 coils, you have to check each. Being MPI, you could have a dead cylinder because a plug was broken or a wire knocked off and may not even notice it.
Have any alarm horns sounded?

With the engine running, you should be seeing 14+ volts. Check it with a DVM directly on the battery

Re: 8.1 GI low rpm

I have not checked the plugs or wires. What is the best way to check for spark at each wire? Would the low voltage keep the fuel pump from working 100% or is a yes or no deal.

Re: 8.1 GI low rpm

Don, does the 8.1 Volvo have an equivelent computer to a Mercury Smartcraft? If so, take it to a dealer or mechanic and have them read any codes it's set, then go from there. Probably the cheapest and quickest way to get it going again in the long run.

Re: 8.1 GI low rpm

ACV97 said:

I have not checked the plugs or wires. What is the best way to check for spark at each wire? Would the low voltage keep the fuel pump from working 100% or is a yes or no deal.

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Might as well take it to a dealer, if you don't know how to check for spark, troubleshooting any MPI problem is way beyond your capabilities.
You will need at minimum, an OEM service manual, a DVM and really know how to use it, and some sort of diagnostic tool (NOT automotive) to read codes and other sensors, along with test for injectors, a fuel pressure gauge and adapters to check fuel pressure.

Re: 8.1 GI low rpm

How fast was she before? MPH, GPS . . . RPM? Which Four Winns?

BTW, forget revving her in neutral and absolutely meaningless

Re: 8.1 GI low rpm

It is the 240 Horizon which would do in the mid 50's before. Don the way I used to check for spark on quads and bikes was kick the motor over and watch for spark, I figured there is a better way. I will pull a few plugs just to see how they look and double check the alternator. If the local mechanic will loan me his code reader than I might be able to plug get the codes as well. Will a bad plug or low spark with the EI show on the codes or is this something that needs to be found manually?

Re: 8.1 GI low rpm

Changed the plugs and WOW new boat. Here is the question why would the alternator be affected by changing the plugs? When engine ran poorly at 2000 RPM the tach volt meter bairly said 13. Changed plugs and at 2000 RPM the volt meter is at 14. I assume it has something to do with the EI.