This is such a great source of information to solve issues or point people in the proper direction, so I wanted to tap into the knowledge base. I have a 2007 220 with the 8.1 GXI. Has been running great but suddenly down on power. Was out for a drive at normal speeds and then went into a larger cove where we were just moving along at trolling speeds. When I went to get back on it, the engine was lagging for sure and slowly got up to speed but something clearly amiss. Sound was a little off but no smoke or other tell tale signs, gauges looked good, so restarted a few times to see if might clear but didn’t. Ended up bringing it back to the dock and it visually checked out.
As a first course of action, I changed out the plugs as these hadn’t been done in 2 years. Went with the NGK TR55GP gapped to .060 (add or subtract a 0 + fuel filter was just changed in the spring, as was the impeller). A quick test drive showed that this surely helped but I didn’t have time to take it for an extended run. Fast forward 1 week and I was able to take it out to see if all ok. The acceleration was much better but not what the 8.1 should have. Could only get about 4600 rpm's and a GPS app said 49 mph, so some power missing somewhere.
Any ideas? Coils? There is a low and high side so maybe the high side isn't working and only getting full output from 7 of the 8 at the top end? Fuel filter clogged? I found a post online about a Fuel Anti siphon valve from the tank that can collapse causing loss of high rpm's.
I do most of my own work on cars that have ranged from high rpm 4's (Acura's, Honda's, VW's), Turbo Boxer 4's (Subaru), V-6's (Honda, Audi's), but sadly, never a V-8. So why wouldn’t I want to jump right in and get a Big Block?
Each has their own unique sounds, vibrations and challenge points, just havent had enough time with the GXI to get a handle.Thanks in advance for your advice and consultations.
