MacsBrendella23 Posted June 18, 2021 Share Posted June 18, 2021 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. Link to comment Share on other sites More sharing options...
Baller BraceMaker Posted June 18, 2021 Baller Share Posted June 18, 2021 Wires points rotor cap? Link to comment Share on other sites More sharing options...
Baller WIRiverRat Posted June 18, 2021 Baller Share Posted June 18, 2021 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. Link to comment Share on other sites More sharing options...
Baller 2Valve Posted June 18, 2021 Baller Share Posted June 18, 2021 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. Link to comment Share on other sites More sharing options...
Baller MDB1056 Posted June 18, 2021 Baller Share Posted June 18, 2021 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. Link to comment Share on other sites More sharing options...
Baller BraceMaker Posted June 18, 2021 Baller Share Posted June 18, 2021 @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. Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 Could it be my fuel/water separator? I have a new one but just haven’t put it on yet Link to comment Share on other sites More sharing options...
Baller LeonL Posted June 19, 2021 Baller Share Posted June 19, 2021 Misfire, (somewhat ambiguous term) is usually related to ignition. This is especially true if it occurs at times other than acceleration. Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 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. Link to comment Share on other sites More sharing options...
Baller riplash Posted June 19, 2021 Baller Share Posted June 19, 2021 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. -Ryan Link to comment Share on other sites More sharing options...
Baller LeonL Posted June 19, 2021 Baller Share Posted June 19, 2021 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). Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 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 Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 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 ??♂️ Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 I found 351w firing order to be 13726548 Got that completely dialed in and still no luck. Link to comment Share on other sites More sharing options...
Baller eyepeeler Posted June 19, 2021 Baller Share Posted June 19, 2021 You may want to think about "very carefully" unscrew your throttle knob....then very carefully install the knob on a '93 Mastercraft. Link to comment Share on other sites More sharing options...
MacsBrendella23 Posted June 19, 2021 Author Share Posted June 19, 2021 Lol if only Link to comment Share on other sites More sharing options...
EricE Posted June 20, 2021 Share Posted June 20, 2021 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. Link to comment Share on other sites More sharing options...
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