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Swing and a miss

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  • Swing and a miss

    New cap and rotor, sparkplug wires and plugs. Sounded awesome in the the driveway, not so much on the lake. Low RPMs I'm getting a miss. Checked and and rechecked my wires on the cap and plugs, all feel connected properly. I'm guessing a bad wire possibly arcing somewhere but not positive. Open to any suggestions.

  • #2
    What prompted the maintenance? Same issue?
    upper rpm it runs ok?
    batteries fully charged?

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    • #3
      Just doing regular maintenance, didn't have any issues before. Which is crazy cuz the cap and rotor looked pretty bad.

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      • #4
        Oh yes sir batteries got charged before I went out today, higher RPMs didn't seem to be effected. It's obvious at low RPMs especially in gear.

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        • #5
          Well that’s some strange chit! Around what rpm does the Miss go away?
          do you still have the old parts? Maybe put them back on one at a time to find the culprit
          if it’s like my engine there is a sensor on the back of the intake, can’t remember if it has a hose connection and wires or just wires maybe that got disconnected?
          what brand and part numbers did you get for cap, rotor and wires?

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          • #6
            I agree its a pretty straight forward deal, or so I thought. The old parts went to dumpster heaven I'm afraid. The cap, rotor and wires were Quicksilver brand. I don't recall the plugs specifically. The miss seems to go away around 1500-2000 RPM's. I would have a hard time believing it would be a plug, but you really just never know. I'm going to pull the cap today after work and make sure there's not any moister in there. It's going to be 103 degrees today so should be a grand time. If nothing is obvious, I might run it tonight when it gets dark and see if anything is arcing. Other wise I'll just start pulling and replacing piece by piece. Its really got me stumped, but then again thats not hard to do.

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            • #7
              I’ve seen rotors do strange things but you’d think the problem would be throughout the rpm range.
              since you don’t have the old parts (shame on you) I’d go to the local parts store and get the cheapest cap and rotor, doesn’t matter if it’s aluminum contacts instead of brass for test purposes.
              here’s the bwd numbers any store should be able to cross, if not 1992 Chevy 1 ton 454
              cap = C266
              rotor = D220

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              • #8
                Thanks buddy, I'll give it a shot

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                • #9
                  Originally posted by Kefurr View Post
                  I’ve seen rotors do strange things but you’d think the problem would be throughout the rpm range.
                  since you don’t have the old parts (shame on you) I’d go to the local parts store and get the cheapest cap and rotor, doesn’t matter if it’s aluminum contacts instead of brass for test purposes.
                  here’s the bwd numbers any store should be able to cross, if not 1992 Chevy 1 ton 454
                  cap = C266
                  rotor = D220
                  Still going to try the cap and rotor, that being said........Yesterday took her out and ran her at 3500-3700 RPM's for half an hour. Ran beautiful with no issues. when I got back down to idle speed no miss at all. BTW any idea what temp thermostat the 502 should be running? I'm guessing 180. The previous owner did some interesting maintenance stuff I'm constantly discovering. Really wouldn't be surprised if there wasn't a thermostat at all. I also noticed for the first time yesterday my volt meter at idle was around 10 and at speed was at 12, wonder if that is not sending enough voltage to the distributor causing the miss.

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                  • #10
                    thermostat should be 160, GLM marine sells a kit part 13101, thermostat, gaskets and sleeve. do not buy a thermostat and gasket from local parts store, gasket has to have the brass inserts for sensors to work correctly. voltage not good, chasing the gremlins like I did earlier in the year. start by eliminating a bad ground, take a pair of jumper cables and connect both negative terminals on your batteries to the engine then check your gauge to see if different. do you have a mercruiser scan tool? I think my stock alternator is around 13.5 with blower off, don't think it changes much from idling to running.
                    and yes the low voltage could be your ignition miss problem.

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                    • #11
                      Im going to suggest to admin this forum be renamed to Baja Boat Owners forum by Kefurr, you are the man. I will get the kit for the thermostat ordered today. I actually went thru some wiring in the spring and discovered most of my grounds to the block weren't even finger tight. I will definitely put the jumper cables to the block and batteries. I assume the motor should be running?

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                      • #12
                        Yeah, motor running
                        unfortunately it’s probably a testament of past problems on boats! 🙈🤬🤣

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