96 PCM GT40 bogging under acceleration.

[wwuboarder82]

Hey,

My GT40 recently started bogging down when I try to accelerate. If I go easy on the throttle I can get it up to a plane and going about 25mph but if I try to push the throttle harder it bogs down and doesn't seem to give me any more power. At times it will act like it's going to stall when I do this also.

Any ideas where to start?

Thanks!

[Chexi]

One possible place to start is replacing the inexpensive fuel relay.

[Polar Express]

Well, I'm new to the forum, and I saw your thread while looking for other data. I'm quite familiar with mechanical issues, just need to learn the boating nuances.

The symptom you are describing is common when your engine is not allowed enough fuel to do what you are asking it to do.

Before the relay, I'd replace your fuel filter. Here's why: Under acceleration of any kind (car, truck, boat, etc.) The engine requires more fuel to accelerate than to maintain speed, at a given load. If the fuel filter is starting to become plugged, the filter media won't allow the pump to push enough fuel through to allow for acceleration. But, if you can 'baby' it up to a speed, the engine doesn't require the same volume of fuel as a hard/normal acceleration.

Normally, a relay won't flicker on and off (sure it could happen, but not likely) which would need to happen to produce a lower fuel volume. A mostly occluded fuel filter will still allow the fuel pressure in the supply to the injector unit (TBI or fuel rail) to build to proper levels, under no load, but as soon as you open it up, and the engine wants more fuel, it falls flat on it's face. If you can have a friend watch the gauge when you do this, and the pressure drops, that's almost certainly it.

In a EFI situation you need both pressure and volume. Pressure to allow the injectors to work properly, and volume to keep up with demand. In a carb, you just need volume, because the vacuum generated by the air passing the venturi of the carb actually sucks the fuel from the float chamber.

Now, if your filter is new, and clean, and you still have the issue, your fuel regulator may be acting up, or, your pump could be wearing out. These are normally NOT the case, but it has happened. Normally, an electronic fuel pump doesn't slowly wear out, it just quits. So the clogged filter or blocked fuel pickup is a FAR more likely scenario. Even if the filter is new, there is a possibility you could have picked up a bad batch of fuel, or some dirt-bag could have vandalized your boat. The reason I share this, is that just because you change your filter, doesn't mean that's the end of it. If you have crud in your fuel, you may have to change several filters before you actually catch all the crud in your gas. If, when you change your filter, and go right out and the boat wakes back up, and runs normally.... but then the symptoms return, that's what is most likely. Depending on how fast the symptoms return, you may decide to just buy several filters, and go that route, or if it returns super fast, you may want to drain your fuel tank, flush it, and start over. (this is NOT fun)

It is very important to use good fuel filters, with high surface area, and low micron filtration. Your injectors will thank you for it!

If you have any questions, feel free to PM me, or post here. I'm new here, so I'll be learning a lot myself.

PE

[NAVYFLYER]

Gt-40

Check the black three inch fuel line connected to the low pressure fuel pump inside the fuel water seperator. Big failure item on these motors. I had mine fail last year. It is a cheap part that will render your boat useless. I was told correct craft should have recalled it but for whatever reason did not.

[Chexi]

I'm telling you... start with the relay. The relay is cheaper and way easier than changing the fuel filter. The GT-40 uses the Fuel Control Cell instead of the typical fuel filter found on many other engines. If you have never taken it off before, it is a real bear the first time. You will need 2 strap wrenches to do it, and you will think you are going to break it before it breaks loose (search FCC on this site... you will see). Fuel filter problems are rare in the FCC. They happen, but less frequently than fuel relay problems. For some reason, the fuel relay on the GT-40 is a lot more susceptible to failure than a relay should be.

If that's not the problem, then you have an extra relay for when it is the problem, which will eventually happen. The same relay is used for the EPM, so it's good to have a spare.