Recently I've noticed that I cannot get the rpms out of my 3GM30F engine that I usually get. Specifically, she maxes out at about 2000 rpm. Otherwise it starts and runs fine. Is this a symptom of something?
Why is my 3GM30F Slowing Down?
- Thread starter markwbird
- Start date
I'd guess either fouling of the prop or bottom, or carbon building up in the exhaust elbow. Any unusual smoke from the exhaust when under load? Also, does it max out there only when under load, or in neutral too? If it's a problem in neutral I'll add tachometer circuitry to the guesses.
On my 2gm it lost power soon after exhaust change. Changed all filters. Then turned out to be injectors. It would run when I engaged 1 compression relief lever but die when I engaged other
How about boat speed? Are you experiencing black engine smoke or a hard pull on the steering wheel? These could be signs of a fouled bottom or prop. The first thing is to determine if the tachometer reading is reasonably accurate. A loss of power and boat speed should be felt along a slow RPM reading. If it is determined the loss of RPM is accurate then, the #1 cause for your symptoms are bad fuel or clogged primary and secondary fuel filters. Check the fuel lift pump for leaks and bleed the fuel lines for any trapped air. If these are good then make sure the air intake tube is clear of any obstruction and that the exhaust mixing elbow is not clogged. Injectors and incorrect valve lash would likely make the engine run rough which you report is not. Good luck.
Not enough info to solve this puzzle. I've had the same problem. The two fixes in separate incidents were fuel filter and exhaust backing up. In my exhaust problem the engine would run strong for a minute or two, then gradually get rougher until it would shut down. Letting it sit for a minute , the engine would fire up strong and repeat the process
Mark - give the scenario, my gut feel is it's the mixing elbow. Not cheap and, potentially, lots of work to change it out if the coupling doesn't want to budge.
Try doing this: Disconnect the water hose on the top of the elbow and look inside the pipe fitting that tees into the elbow. If it has a lot of crud inside, enough that the passageway is being restricted, then that would be an indicator the elbow hasn't been changed in a while.
If there is measurable scale crud there then there is almost certainly carbon inside the elbow area. Get a new elbow and, to save time, a new coupling - in case the old one is too difficult to take apart - and change it out. If that doesn't solve the problem then just save the old one for the future as an emergency replacement.
After several months the carbon in the old one will dry out and start falling out. If there is a sign of any crack in the side of the old elbow then it is toast.
If the issue persists, then changing out the filters would be a good next effort. One at a time then test if there is any difference in how it runs. If both are changed at the same timed the issue goes away you won't be able to tell which one was the problem.
Still a problem, or fixed it, come back and let us know...
Try doing this: Disconnect the water hose on the top of the elbow and look inside the pipe fitting that tees into the elbow. If it has a lot of crud inside, enough that the passageway is being restricted, then that would be an indicator the elbow hasn't been changed in a while.
If there is measurable scale crud there then there is almost certainly carbon inside the elbow area. Get a new elbow and, to save time, a new coupling - in case the old one is too difficult to take apart - and change it out. If that doesn't solve the problem then just save the old one for the future as an emergency replacement.
After several months the carbon in the old one will dry out and start falling out. If there is a sign of any crack in the side of the old elbow then it is toast.
If the issue persists, then changing out the filters would be a good next effort. One at a time then test if there is any difference in how it runs. If both are changed at the same timed the issue goes away you won't be able to tell which one was the problem.
Still a problem, or fixed it, come back and let us know...