Phazar454Mag

I have bought a used 454 Mag MPI 1999 model (cool fuel - MEFI3) 245 running hours. It runs real strong, but it smells of unburned fuel and it leaves a small trail of fuel in the water when running at idle (even after having warmed up). I went to the local dealer and borrowed the DDT, no codes have been logged. Unfortunately my local dealer knows very little about engines such as the 454 Mag MPI, so he can't answer any questions. The only thing that concerned me was a MAP sensor value of 2.9V (with a Baro sense value of 4.98V). I will check the vacuum tomorrow from the intake manifold to see if it explains the MAP sensor value. But I would also like to check the fuel pressure. But where can I connect a fuel pressure gauge on my engine ?
BTW my plugs are brown so I am pretty sure it is getting too much fuel.

GOODT

At The Schrader Valve

Dave_N

There are several things that can cause a rich condition and/or unburned fuel smell and on an EFI system. Cylinders(s) not firing, injector leak, bad sensor (will usually trigger a trouble code) and high fuel pressure are the most common.

The MAP sensor voltage 0f 2.9v indicates a vacuum of about 11" Hg. It's a little low, a disconnected vacuum line at the fuel pressure regulator could cause low vacuum and rich condition at idle.

The fuel pump pressure should be 41 to 45PSI. If it's higher than that, check for a clogged fuel return line screen. It's not an uncommon problem on a Cool-Fuel system.

Dave

Phazar454Mag

Finally managed to get hold of a fuel pressure gauge, and the result is that fuel pressure drops immediately to 0 after the fuel pump stops. I turned the ignition key like 4 times to check the max. pressure, and that was 45 PSI. But drops right after the fuel pump stops. I then tried starting the engine, and for the first time ever it did not start immediately when cold. I assumed the engine might be flooded in case 1 or more injectors were leaking. Tried to start again and it fired OK. Let it run at 1000 RPM for a couple of minutes and then turned off the engine. Checked the plugs and 4 were wet and 4 dry. I then started again and took the boat for a spin at high speed to get the plugs dry. It was successful and all plugs were dry. I then turned the ignition key on several times to engage the fuel, without trying to start the engine, and then used a remote starter switch to turn the engine over without firing the injectors. Checked the plugs and they were all dry ? Started the engine and let it idle a few minutes, and then checked one of the plugs that were wet the first time. This time a very small area were wet on the plug.
Any advice of what is going on ?
Do I have 1 or more leaking injectors and how can I really determine that ?
I actually borrowed a DDT tester, but since the fuel pressure drops immediately I can't do a balance test by firing the injectors via the DDT.
Thanks.

Vinny P

Those injectors are batch fired. This means that one side of the enigne fires at a time, not individual injectors..

Phazar454Mag

Just returned from the dock again, and there is no longer any doubt in my mind: I have 1 or more leaking injectors. I switched the ignition on 6 times to let the fuel pump build up pressure before starting the engine, and the result: It wouldn't start. The engine was flooded. Checked a few plugs, and some were wet and some dry. Got the engine started and a lot of unburned fuel in the water behind the boat. Guess it is time to buy some new injectors. Surprised this can happen on an engine from 1999.