Getting rid of 100 gallons is never an easy task....but a headache that is less severe than destroying two 4.3's........

Sounds like detonation to me also, those 175 gl plastic tote's are cheap, Id dump it all and start fresh

New fuel filters and im back to clean fuel now, I think the contaminants I saw may have been rust falling off from the top of the filter when i dumped it. I have ran each engine for a couple minutes each and all fuel I have dumped from the filter is clean. I checked fuel pressure, and the starboard motor ran around 40 psi, and the port motor around 35 psi. The port motor is the one that wouldnt spin past 3800 rpms, and it has now developed a backfire through the exhaust at idle. The backfire goes away when you increase RPM, but pretty consistent at idle.

What is the fuel pressure supposed to be ? I think I would stop and do a compression test and maybe a leakdown test on the port engine. Sounds like it might be starting to burn a valve or if it was detonating bad enough it might have tuliped the intakes :(

I am unsure what the fuel pressure is supposed to be. 40 seems closer to what it should be than 35, I looked for some markings on the regulator but could night find anything.

Before all this happened I did a compression test on both motors and all 12 cylinders were between 150-155. Have not done a compression test since having the issues. Thinking back I do kind of remember hearing a backfire at idle from the port motor when we first started it up for the day. I also replaced the distributor on that motor earlier this year, maybe I put it in 1 tooth off? Even 1 tooth off though would it still be able to reach 3800 rpm?

I think you have a fuel pump problem. Don't the MPI motors have a low and high pump? If so, the low pressure pump is failing.

That bad gas did a number on your motors.....

I do not believe these have a high and low pressure pump. Just the cool fuel module under the motor mount on the port side.

I'm quite certain there was at least a couple backfires at cold idle from the port motor before we had the issue with the knocking/ticking. It just does it more now. And also just to be clear, the knocking/ticking is gone and was gone for the last 30 minites of our trip. Everything was back to the way it was before the knocking/ticking for the last 30 minutes of our trip.

How did you time the engine after reinstalling the distributor.

I marked the distributor before removal, and then put the new one in the same position. Then used a timing light to verify the mark on the balancer was in the same position at idle as the other engine. There is no adjustment on the distributor, and only 1 mark on the timing cover

I just put 2 brand new fuel filters on and did fuel pressure test again with a different tester. Both motors go up to 40 psi with the key on. Port motor drops to 35 psi When running, starboard side stays at 40 psi. Port motor still back firing every 7-10 seconds at idle, does not backfire at any other rpms. Possible injector sticking open that is causing the loss of fuel pressure and backfire?