1999 Supercharged 454 problems
 

Can anyone please help me? I have my boat into the repair shop and its getting expesive to try to diagnose the problem. What I have is a 1998 2330 Chaparral with a 7.4 Mercruiser and an addon 5lb boost procharger with inner cooler.
I noticed one that the thermostat has been removed. I put one in at 160 degree, but now am being told no thermostat is the way to go on this moter with the charger.
My big problem is the motor cuts out very badly at 3800 rpm. If I trim down and push water it cuts out even worse. Feels like there is much more rpm and power it wants to put out, but something is telling it to not go there. Any thoughts?

Is it getting fuel? Have you checked the plugs to see what they look like?

Becareful with the 7.4 under boost with problems. Don't want to burn a piston.

I would remove the thermostat, or go to a 140 unit. This will help to keep detonation away. Remember a 160 thermostat STARTS to open a 160, and isn't fully opened til about 180. Is the motor carbed or fuel injected?




Darrell.

It seems to be getting fuel although when its cutting out the pressure is bouncing from 10-50, but it seems to run rich. It's getting the plugs changed today and the compression is good at 150 on all cylinders. The plugs before where not the recommended plug so I put the in the NGK 5. It seems electronic based on how quickly it tries to recover after the cutouts.
I've checked vaccum lines but not the fuel filter etc. Have you ever heard of removing the thermostat in these motors with a charger to keep the charger cooler? Seems to me I want some heat in the motor? Also any idea what a the WOT rpm should be...46-4800?

So, you obviously have a fuel pressure gauge installed. If the pressure is erratic when it starts to cut out, I believe you have determined it is a fuel problem and not an ignition problem. Start with the easy stuff like changing the fuel filter, making sure you do not have a soft fuel line collapsing on you, etc. 4,600 is max RPM.

Exactly. Check all the easy stuff. Pump, filter, seperator, etc..

Pressure should not jump around.

Did you just add the ProCharger?

Or it has worked correctly and now is just experiencing this problem.

Like stated in the previous post, I would be looking at a fuel issue if the gauge is bouncing around to 10PSI.

Is the anti siphon valve out of the gas tank?

Procharger recommends no thermostat!

Thanks all! One more...
The mechanic just called and it doesn't appear to be pulling water in from the ports on the lower unit? I had it out two nights ago and it was moving water as I could see it coming out of the exhaust, plus I could see the water temp go up and down based on how I was running so I know it was getting water. could there be a blockage in the water movement to the engine causing it not to suck water? I'm sure the impeller was ok the other night.

You may have a water restriction problem, how high does the temp get while you are running? The water temp should not change that much. I am running without a t-stat and my oil temp creeps up when I run hard and comes right down but the water stays pretty constant.
Scott