496 HO Falling flat around 4000 RPM
07-14-2018 | 08:34 PM
#1
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496 HO Falling flat around 4000 RPM
Guys,
i just bought a 2003 Sonic Prowler with a 496 HO. The previous owner had health issues and hadn't used the boat in 2 seasons. I have known this boat since it was new and the previous owner took great care of it. We charged the batteries dropped it in the water and it started right up. It pulls out of the hole like a freight train. Runs perfect at 3500 rpm but when you get on it it falls off at 4000 rpm and starts to lose power. If you pull back on the throttle it comes back. It backfired through the exhaust a few times when I idled through a no wake zone. Off idle response is really good. What do you guys think this could be? The gas is old not sure exactly but over a year old.
Kevin
i just bought a 2003 Sonic Prowler with a 496 HO. The previous owner had health issues and hadn't used the boat in 2 seasons. I have known this boat since it was new and the previous owner took great care of it. We charged the batteries dropped it in the water and it started right up. It pulls out of the hole like a freight train. Runs perfect at 3500 rpm but when you get on it it falls off at 4000 rpm and starts to lose power. If you pull back on the throttle it comes back. It backfired through the exhaust a few times when I idled through a no wake zone. Off idle response is really good. What do you guys think this could be? The gas is old not sure exactly but over a year old.
Kevin
07-14-2018 | 09:19 PM
#2
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From: Ft. Worth TX
so what testing have you done ? Scan the engine? fuel pressure testing ? spark testing with the proper testers ? Are all the coils firing ? Spark plugs look good - how about a compression test - ohm out the spark plug wires ?
Scanning the engine ? is it in guardain mode ? What is available power showing ? What fault codes ? What are the running parameters are they in spec ?
be prepared for the dart throwing contest here without any testing period with the feedback results, Sorry cause that the way it is with any MPI engine - MPI engines need proper testing to pin point issues period.
First I would scan the engine and know how to read it. I would next move on with fuel pressure testing and running the engine on a portable fuel supply to eliminate which side the issue(s) is coming from ie : boat side or engine side especially since the boat sat. Fuel pressure is important and rock steady readings. --- Next I would test for spark with sealed inline spark checkers on all 8 thru the rpms. Without any of this I suggest finding a great Merc tech who knows the 496 very well. Or Im in Texas can fix this without an doubt. .
Next and never rule out the fuel injectors restricted from contamination. Do not rule that out. And Im in Texas for that service as well. Simple mail out and mail back when done
Scanning the engine ? is it in guardain mode ? What is available power showing ? What fault codes ? What are the running parameters are they in spec ?
be prepared for the dart throwing contest here without any testing period with the feedback results, Sorry cause that the way it is with any MPI engine - MPI engines need proper testing to pin point issues period.
First I would scan the engine and know how to read it. I would next move on with fuel pressure testing and running the engine on a portable fuel supply to eliminate which side the issue(s) is coming from ie : boat side or engine side especially since the boat sat. Fuel pressure is important and rock steady readings. --- Next I would test for spark with sealed inline spark checkers on all 8 thru the rpms. Without any of this I suggest finding a great Merc tech who knows the 496 very well. Or Im in Texas can fix this without an doubt. .
Next and never rule out the fuel injectors restricted from contamination. Do not rule that out. And Im in Texas for that service as well. Simple mail out and mail back when done
Last edited by BUP; 07-14-2018 at 09:23 PM.
07-15-2018 | 05:37 AM
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Ok so far I've done no testing. It appears that I am a bit unprepared to deal with this particular MPI technology. My last boat was a 1989 wellcraft scarab with twin carbureted 454s. My car is a 66 Impala so I will be on a steep learning curve.
Lets start with the simple stuff. What type of scanner do I need? Can anyone recommend a decent one that is budget friendly? Let me clear that statement up. I understand this stuff can be expensive that's not the issue. I am a recreational boater not a repair shop and not a race team. I enjoy tinkering and figuring things out for myself (with help from my friends like you great people). So that being said what brand / model scanner would do the job reliably?
I will do some research as well but does the scanner stay stay plugged in while you run the engine and does it provide Fuel pressure readings from the on board sensors or do I need another type of verification? I really have a lot to learn. Is there a good book available to learn about these motors and technology?
kevin
Lets start with the simple stuff. What type of scanner do I need? Can anyone recommend a decent one that is budget friendly? Let me clear that statement up. I understand this stuff can be expensive that's not the issue. I am a recreational boater not a repair shop and not a race team. I enjoy tinkering and figuring things out for myself (with help from my friends like you great people). So that being said what brand / model scanner would do the job reliably?
I will do some research as well but does the scanner stay stay plugged in while you run the engine and does it provide Fuel pressure readings from the on board sensors or do I need another type of verification? I really have a lot to learn. Is there a good book available to learn about these motors and technology?
kevin
07-15-2018 | 07:36 AM
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From: Tygart Lake, WV
Rinda Technologies marine diagnostic tools, marine diagnostics, marine scan tools, marine engine software
Latest offering is the Techmate Pro. Yes. It can stay plugged in and monitor engine functions while running. To test fuel pressure....you want a dedicated fuel psi test kit and hook into the valve on fuel rail. Key on engine off 42-3 psi.
Best place to learn of the 496 is here.... search this forum. There are thousands of posts with good info.
Last edited by Ryan00TJ; 07-15-2018 at 07:40 AM.
