496 HO MAG Running Rough Missing
#21
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To catch up.....Boat runs 74MPH top speed on GPS. Port Engine runs 4,900 and starboard runs 4,600rpm by the tachs. when gassing the throttle in neutral from idle to approx. 2,000rpm and back real quick the engine pops/backfires out the exhaust when almost back to idle. any thoughts?
#23
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Reving in N on the water hose or in the water by THROTTLE ONLY only will set the overspeed code hence drops ignition but should set off the warning beeps to - so is your warning horn active while this backfiring is taking place and or throttling in persay N . Your test here with the back firing - does this happen when you are truly driving the boat on the water in gear running forward - throttling up and back - ( accelerating and deceleration running in gear) ?
Overspeed usually sets at 2500 rpms give or take a few here when throttle up in N (persay) - I say persay because it really is called reving in throttle only .
Overspeed usually sets at 2500 rpms give or take a few here when throttle up in N (persay) - I say persay because it really is called reving in throttle only .
Last edited by BUP; 01-17-2015 at 06:54 PM.
#24
I had a crankshaft position sensor that went south, but was throwing no codes. It was causing RPM loss and weird issues that I thought was a fuel problem. I did a LOT of troubleshooting like fuel/pressure/quality/filters/boost pump; and spark plugs/wire/spark test/misfire tests...
...but BUP aka John helped me narrow it down to the CrankPS.
BUP will know for sure, if you can provide your serial numbers (if you have them), but I have also had to replace my fuel boost pumps due to bad fuel issues (several years earlier than aforementioned problem). I bought fuel in FL that was was labelled and advertised as non-ethanol; but turns out it was after we tested it. I left it sit in the tanks (untreated) for a few months in Florida humidity and it ruined inline filters, f/w separators, and fuel boost pumps on both of my 496s when I fired up the boat for the season back in Virginia.
...but BUP aka John helped me narrow it down to the CrankPS.
BUP will know for sure, if you can provide your serial numbers (if you have them), but I have also had to replace my fuel boost pumps due to bad fuel issues (several years earlier than aforementioned problem). I bought fuel in FL that was was labelled and advertised as non-ethanol; but turns out it was after we tested it. I left it sit in the tanks (untreated) for a few months in Florida humidity and it ruined inline filters, f/w separators, and fuel boost pumps on both of my 496s when I fired up the boat for the season back in Virginia.
#25
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Thanks for the post Brian. Will add why I posted in post # 23 that response was because in post 21 OP says running at 73 mph plus has some rpm differences from one motor to the next as that can be anything for the cause of that. It could be prop related, engine related problem, sensor related problem, fuel related problem, and including is the engine throttle plate able to achieve wide open position. Anyways his posts ONLY states "while gassing in N " never any mention of back firing while running. Just saying
IMO if a clear description of running issues and a list in order of things that has been checked along with parts changed out, sure would help to determine what the real issue is. Also OP mention from the scan motor(s) are showing 100% available power or am I not correct about this ?.
If all possible post your scan report. I would think this boat is put to bed being in Michigan but the engine still could be scanned during this timeframe without running the engines. . Again just saying and sticking with it, trying to help.
IMO if a clear description of running issues and a list in order of things that has been checked along with parts changed out, sure would help to determine what the real issue is. Also OP mention from the scan motor(s) are showing 100% available power or am I not correct about this ?.
If all possible post your scan report. I would think this boat is put to bed being in Michigan but the engine still could be scanned during this timeframe without running the engines. . Again just saying and sticking with it, trying to help.
Last edited by BUP; 01-18-2015 at 12:19 PM.
#26
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Reving in N on the water hose or in the water by THROTTLE ONLY only will set the overspeed code hence drops ignition but should set off the warning beeps to - so is your warning horn active while this backfiring is taking place and or throttling in persay N . Your test here with the back firing - does this happen when you are truly driving the boat on the water in gear running forward - throttling up and back - ( accelerating and deceleration running in gear) ?
Overspeed usually sets at 2500 rpms give or take a few here when throttle up in N (persay) - I say persay because it really is called reving in throttle only .
Overspeed usually sets at 2500 rpms give or take a few here when throttle up in N (persay) - I say persay because it really is called reving in throttle only .
#27
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I had a crankshaft position sensor that went south, but was throwing no codes. It was causing RPM loss and weird issues that I thought was a fuel problem. I did a LOT of troubleshooting like fuel/pressure/quality/filters/boost pump; and spark plugs/wire/spark test/misfire tests...
...but BUP aka John helped me narrow it down to the CrankPS.
BUP will know for sure, if you can provide your serial numbers (if you have them), but I have also had to replace my fuel boost pumps due to bad fuel issues (several years earlier than aforementioned problem). I bought fuel in FL that was was labelled and advertised as non-ethanol; but turns out it was after we tested it. I left it sit in the tanks (untreated) for a few months in Florida humidity and it ruined inline filters, f/w separators, and fuel boost pumps on both of my 496s when I fired up the boat for the season back in Virginia.
...but BUP aka John helped me narrow it down to the CrankPS.
BUP will know for sure, if you can provide your serial numbers (if you have them), but I have also had to replace my fuel boost pumps due to bad fuel issues (several years earlier than aforementioned problem). I bought fuel in FL that was was labelled and advertised as non-ethanol; but turns out it was after we tested it. I left it sit in the tanks (untreated) for a few months in Florida humidity and it ruined inline filters, f/w separators, and fuel boost pumps on both of my 496s when I fired up the boat for the season back in Virginia.
#28
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Thanks for the post Brian. Will add why I posted in post # 23 that response was because in post 21 OP says running at 73 mph plus has some rpm differences from one motor to the next as that can be anything for the cause of that. It could be prop related, engine related problem, sensor related problem, fuel related problem, and including is the engine throttle plate able to achieve wide open position. Anyways his posts ONLY states "while gassing in N " never any mention of back firing while running. Just saying
IMO if a clear description of running issues and a list in order of things that has been checked along with parts changed out, sure would help to determine what the real issue is. Also OP mention from the scan motor(s) are showing 100% available power or am I not correct about this ?.
If all possible post your scan report. I would think this boat is put to bed being in Michigan but the engine still could be scanned during this timeframe without running the engines. . Again just saying and sticking with it, trying to help.
IMO if a clear description of running issues and a list in order of things that has been checked along with parts changed out, sure would help to determine what the real issue is. Also OP mention from the scan motor(s) are showing 100% available power or am I not correct about this ?.
If all possible post your scan report. I would think this boat is put to bed being in Michigan but the engine still could be scanned during this timeframe without running the engines. . Again just saying and sticking with it, trying to help.
#29
Remember, you have a CAM position sensor and a CRANK position sensor.
Cam on front.
Crank on back.
You could also have a prop issue causing RPM difference.
They could not be exactly the same (did you replace one?) or you could have damage that is affecting one's performance vs. the other.
Cam on front.
Crank on back.
You could also have a prop issue causing RPM difference.
They could not be exactly the same (did you replace one?) or you could have damage that is affecting one's performance vs. the other.
Last edited by Sydwayz; 01-19-2015 at 12:32 PM.