8.1L Surging Help (Video)
05-06-2019 | 11:35 PM
#1
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8.1L Surging Help (Video)
I just recently bought a jet boat with a 2009 Marine Power 385hp 8.1L (330 hours) and I was hoping to get some advice or guidance for a technical issue I am experiencing.
I have a video of the problem but cannot post it, as i don't have 10 posts yet.
Under load, primarily in reverse, the engine is surging/pulsing from 2500 rpm down to 1500rpm. It doesn't do it as much in forward. I think it's doing it in reverse because the throttle lever has a much shorter throw in reverse than forward, thus applying throttle faster.
I've checked:
- rail pressure (44 PSI at key cycle)
- 38-40 PSI at idle.
- 38-39 PSI at 3500 rpm.
- checked all spark plugs. They are sooty, dry black indicating a rich condition or weak spark.
Thank you for any help.
I have a video of the problem but cannot post it, as i don't have 10 posts yet.
Under load, primarily in reverse, the engine is surging/pulsing from 2500 rpm down to 1500rpm. It doesn't do it as much in forward. I think it's doing it in reverse because the throttle lever has a much shorter throw in reverse than forward, thus applying throttle faster.
I've checked:
- rail pressure (44 PSI at key cycle)
- 38-40 PSI at idle.
- 38-39 PSI at 3500 rpm.
- checked all spark plugs. They are sooty, dry black indicating a rich condition or weak spark.
Thank you for any help.
05-07-2019 | 09:11 PM
#2
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Joined: Jul 2011
Posts: 9,594
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From: Ft. Worth TX
Jet boat low profile boat and how is your exhaust is routed ? So my guess is in reverse extra exhaust back pressure is creating your issues. as you travel in reverse the stern even squats lower that is putting the exhaust full under water causing extra back pressure against exhaust flowing outward but in forward the stern will raise somewhat and your not having water flowing up and around the exhaust.inwhich is no where close to creating the restriction of back pressure compared to reverse.
05-07-2019 | 09:48 PM
#4
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Thank you for the reply! I hadn't thought of that, but it's definitely not a low-profile boat. This is a welded aluminum river boat not like a race boat. I'll try and get a picture for you. Yes 2500 RPM would be slow in reverse it's barely enough to pull the boat off the trailer. This boat runs a hamilton 212 pump.
05-07-2019 | 11:25 PM
#6
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From: On A Dirt Floor
Do you know of anyone with one of these you can borrow: https://www.rinda.com/marine/marinemenu.htm
So you can read live data and so forth ?
So you can read live data and so forth ?
