After filling up with 87 octane it won’t stay running

[Mondo14]

2014 Moomba Mondo with Indmar 330. Just got it 2 weeks ago, 3rd time on the water with it. First issue.

So at the pumps this weekend my buddy offered to fill it up and he put 87 in it. I forgot to tell him to put 89. Not sure if that’s what has caused this but after about 15 minutes on the water we were going about 40mph and engine started bogging/misfiring(?) and I cut the throttle down and it smoothed out around 3k RPMs. I opened it back up and it started sputtering so I backed it back down and turned back for the dock. It stayed at 3k all the way back with no issues. No fault codes or warning lights. When I got to the dock and put it in idle it stalled. Wouldn’t restart. Today it will start but it’s a very rough idle and stalls shortly after. I’m thinking it’s bad gas or that the 87 octane is causing it. I plan on draining the tank which is 3/4 full and putting 93 in it and seeing what it does. Any other suggestions on what it might be and does anyone think 87 octane would cause this issue?

Thanks!

[secondsupra2004]

You have water in your gas.

[Mondo14]

Thanks. Water in the gas was also something I was considering would cause this. Now to get it all drained and the water out 🤦🏻*♂️

[VA LSV]

Might want to check your spark plugs.

[Holdmybeer]

After you drain the tank, I would add a fuel treatment emulsifier to capture any water/fuel that you could not drain. It will also add some octane in the process and help clean the system out.

I would also find the fuel rail test ports (look like tire valves) and drain fuel out of those. Water can foul out spark plugs, and damage injectors.

[Mondo14]

So after draining the tank, I did find water in the bottom of it. Not a lot but enough as there were puddles of water on both sides near the front of the tank. I was able to gain access thru the front vent with a rag to absorb the remaining fuel and water that I couldn’t get out with my with the siphon hose. Also, somehow on the bottom of the front vent it was not sitting flush on the cylinder part of it. It had a little piece of plastic broken off on the white plastic cylinder piece and the middle piece of it was off center where the spring is. I was able to center it back up before putting it back on but I didn’t see the broken piece inside the tank so who knows how long that had been like that. Should have it back together and filled up with new gas soon and will update if it’s fixed. Thanks for the help!

[HFarr]

So after draining the tank, I did find water in the bottom of it. Not a lot but enough as there were puddles of water on both sides near the front of the tank. I was able to gain access thru the front vent with a rag to absorb the remaining fuel and water that I couldn’t get out with my with the siphon hose. Also, somehow on the bottom of the front vent it was not sitting flush on the cylinder part of it. It had a little piece of plastic broken off on the white plastic cylinder piece and the middle piece of it was off center where the spring is. I was able to center it back up before putting it back on but I didn’t see the broken piece inside the tank so who knows how long that had been like that. Should have it back together and filled up with new gas soon and will update if it’s fixed. Thanks for the help!Sux that you had an issue with it, but great that you found all that. Probably answers your running issues!

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[Mondo14]

Well after draining and drying and filling back up and putting 360 Sta-bil in it to remove any water left in the system and replacing the plugs it still idled rough. So I checked the spark on cylinders and I am not getting spark on cylinders 1,2 and 4. Those spark plugs were soaked with gas when I pulled them and I checked by cranking it with them all out and those 3 had no spark. Now to troubleshoot them.

[Holdmybeer]

Distributor cap and rotor cheap and easy to change.
Mark and then remove....so many people mess up firing order during this job and such a pain to troubleshoot.

[Mondo14]

Changed the cap and rotor, made sure too mark and put wires in their right spots. All have spark now but back to a rough idle that sounds like it’s got a cam and runs smooth at around 3k rpms. All plugs are dry and look good after running it. Gonna put a timing light on it tomorrow and if it skipped time some how.

[HFarr]

Maybe a vacuum leak somewhere

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[Holdmybeer]

You can find vacuum leaks with wd-40. Spray and if the fluid gets sucked in it runs better for a second. Worth a shot.

Timing could easily be the problem. Bolt on distributor could have vibrated loose and twisted some. I believe 5* advanced on older 5.7 GM motors.

[Mondo14]

So after over a month at the local dealer they finally found the issue. It's a bad harness to the injectors causing 4 injectors to not fire. So after changing the cap and rotor, changing the plugs, draining all the fuel, testing the injectors, changing the crankshaft sensor and throttle position sensor, finding no vacuum leaks, they had to order this fuel injector test kit. They said the signal is getting sent out of the ECM but not making it to the injector as this test kit had lights on the injector side of the harness and they could tell the wiring is bad because they weren't lighting up. They said I could try and check the harness for damage and fix it but that they could only replace the entire harness. So I'm going to attempt to troubleshoot this harness and probably end up ordering one and replacing it myself over the winter. If anyone knows a good place to buy the engine harness let me know.

[sandm]

indmar. I'd call them and ask. sure skiers choice or your dealer can source the part but I'd go straight to indmar.

[Mondo14]

Well I finally figured it out and got it running. It was the ECM. Tested the harness with the pin out from Indmar and it was good so ordered an new ECM from inboardonline.com and they had it to me in a few days. Put it all back together with the new ECM and it started right up! So relieved to finally have a working boat but now to wait till spring to get it in the water.

[HFarr]

Maybe it will keep working till then! LOL! When I was in high school, I had a 1972 Dixie Craft with a 105 Chrysler on it. My friends and I would put the water muffs on the foot and fire it up at the house to make sure all was good. We would load up, get to the lake, and 90% of the time it wouldn't start. Take off the cover while floating next to dock and start re-checking everything! Would clean the points, check for fowled plugs, fuel, spark, everything until it would crank. Drove me absolutely crazy as it did that so often. Once it decided to crank at the lake, it was good all day though. We were determined that we drove through some mysterious Burmuda Triangle zone on the way to the lake that just scrambled everything! Or the boat was like Christine and just did it to mess with us!! Hopefully your boat likes you and will crank again as it should when you put it back in the water!

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