PCM 351w

Replaced the spark plugs & adjusted the distributor to get it tuned up.

Got on the water today for the first time since my last post on here. Was running great. Took a few laps, chilled out and turned it off.

Turned it back on, temp was good, impellers weren’t hot, nothing unusual. Started tubing and it developed a misfire again, around 25-30mph is what I believe it started happening at first. Then about every time we have it power it would misfire 2-3 times. Even out and do it again after about 3-5 minutes

Any ideas on what’s causing the misfire. I’ve read some other forums and seems like a common problem that’s hard to trace down.


  • BraceMakerBraceMaker Posts: 4,968 Mega Baller
    Wires points rotor cap?
  • WIRiverRatWIRiverRat Posts: 76 Baller
    Do you know which cylinder is misfiring? You can wear a thick rubber glove and pull each wire off the cap one at a time to figure out which cylinder is having the issue. Once you have identified the bad one you can then go about replacing the wire, spark plug, check compression etc.

    I just had the same problem this spring at start up. Ended up being a loose connection on the injector to cylinder 1. Tightened it up and everything runs great, but I was able to use this technique and find which cylinder, then verify spark, compression and finally find out it wasn't getting gas.
  • 2Valve2Valve Posts: 428 Crazy Baller
    Any chance you mis-routed one plug wire when changing the plugs? I worked on a boat with your same exact problem and discovered the guy crossed the 2, 4 plug wires by mistake.
  • MDB1056MDB1056 Posts: 840 Crazy Baller
    edited June 18
    I doubt there are points in the Brendella as thought I read from a different posit its a 92? Can't be a crossed wire or would misfire all the time and as I read it that's not the case. If there were no issues prior to your changing plugs and "adjusting" the distributor then return the timing to it's prior position and see if you have the same issue. We're assuming your opened the distrib cap to inspect and make sure everything inside was in good order. Has to be something simple.
  • BraceMakerBraceMaker Posts: 4,968 Mega Baller
    edited June 18
    @MDB1056 hard to say. MC still had points till 1990. I see this behavior often when points and timing are set using feeler gauges and a light and dwell is ignored.

    Also with loose or corroded cap and rotor.
  • Could it be my fuel/water separator? I have a new one but just haven’t put it on yet
  • LeonLLeonL Posts: 2,641 Crazy Baller
    Misfire, (somewhat ambiguous term) is usually related to ignition. This is especially true if it occurs at times other than acceleration.
    Leon Leonard Stillwater Lake KY - SR Driver SR Judge
  • Haven’t heard a misfire when it’s just at idle.
    I’m gonna do a compression test today and see what I’m getting.
    Replace the fuel/water separator and might pull off the spark wires and replace them as well.
  • riplashriplash Posts: 30 Baller
    Intermittant misfires can be difficult to diagnose. My boat and a friends boat did the same thing yours is doing. It turned out to be an ignition coil. When it was cool, the boats would run fine, but when the ignition coil got warm, it gradually quit working right, and it would misfire. When the coil cooled off it would run normally.

  • LeonLLeonL Posts: 2,641 Crazy Baller
    I wasn't referring to idle. More of steady cruising/skiing speed. Did you replace cap and rotor? Not expensive items. You didn't confirm whether this engine has points. If so see @BraceMaker comment (use a dwell meter).
    Leon Leonard Stillwater Lake KY - SR Driver SR Judge
  • To be honest I’m not sure what a point on an engine is.
    I’m pretty green, especially when it comes to anything older and carbed.
    But I did a compression test on each cylinder and it ranged from 115psi to 120psi. From forums I’ve read that is about standard and in operating order.

    I just got my new spark wires and cap that I’m going to put on. But I did notice each spark plug had a decent amount of oil on the threads. Could that be a sealing issue, and could it affect my spark, say oil getting on the electrode end of the plug and causing the misfire?
    So many questions I know but I appreciate the help
  • No I don’t have points, it has a coil pack, which I might end up replacing.
    I just did my wires and cap, now I cant get the boat started. I’ve found many different diagrams. It’s all routed up correctly. This is a head ache 🤦🏼‍♂️
  • I found 351w firing order to be 13726548

    Got that completely dialed in and still no luck.
  • eyepeelereyepeeler Posts: 214 Baller
    You may want to think about "very carefully" unscrew your throttle knob....then very carefully install the knob on a '93 Mastercraft.
    Matt Dillon
  • Lol if only
  • EricEEricE Posts: 14 Baller
    I had an 88 Brendella years ago, the fuel tank vent was low on the hull, and very prone to taking in water. It would bog, not misfire, similar to what you are experiencing. May want to consider dumping out the carb as water can get trapped in the primary bowl, and then causes issues when the accelerator pump pushes fuel to the barrels under acceleration.

    As the boat aged and water seeped through the deck into the flotation foam, the boat sat lower and lower in the water, and the problem just got worse. Water tended to get stuck on either side of the fuel tank, with nowhere to drain.
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