I’ve had an issue over the last 3 years or so and was hoping to get some thoughts on the source of it. I have a 2000 454 Mag MPI with around 400 hrs….the engine runs awesome but has a weird issue every once and a while after it’s been sitting for some time. For the first 2-3 minutes or so after it’s been started it sounds like it’s only running on 7 cylinders or something and then will clear up and then it’s fine the rest of the day. The best way to describe it is like it loses the “Mag” part of the engine and the cam profile sounds like a basic 330hp engine without the Mag style cam lope to the idle. If I try to increase the throttle off idle when it’s doing this it will be sluggish and then very lightly pop a few times and then clear up and then its fine the rest of the day. Over the 3 years or so it’s done this I’ve changed the plugs, cap, rotor, fuel separator, cleaned the IAC, used fuel cleaner, etc. The only thing I haven’t replaced is the plug wires. I have recently pulled all the spark plugs to check them and they’re all great with a light brown. Any ideas what this could be? My buddy’s carbed 330hp used to do this sometimes and he thought it was moisture under the cap or something but I wasn’t sure if it may be one of my fuel injector clogged or if my cap/rotor is somehow letting moisture in or the plug wires are tired? Thanks

ttt, any ideas?

I would suggest pulling the fuel rails and injectors for flow testing and cleaning. You may have an injector hanging up, flowing poorly and or some injector hat screens that are partially plugged. This can cause some of the problems your are seeing. If an injector is flowing poorly that particular cylinder will be running lean and if lean enough things will go south fairly quickly. Ask me how I know....

Best of luck.

Have it scanned. Save time and money. Good luck. Your welcome.

Thanks, I appreciate the info….I had it out Saturday and it did it again but this time it never cleared up so I put it back on the trailer. I pulled every plug last night and some were brown, some were dark brown, and some were almost black. I was expecting to find one white one (like if an injector wasn’t working) but not the case. I took the cap off and the cap and rotor had some minor corrosion but nothing major (they were replaced not too long ago). The strange thing was when I had the boat out on Saturday I felt like the engine temp went up quicker than normal…..I drove it off the trailer to the dock and within like 3 min of running it was up to 160 degrees which seemed quicker than normal. The more I think about it I’m wondering if one of the sensors is bad which is telling the computer to adjust the timing which is making it lose power and have such a blah sounding idle? I know you recommended getting it scanned but I’ve read that the self diagnostics on these engines isn’t very good and I’m trying to see if I can figure it out myself first. Does this sound like a bad MAP or Temp Sensor? Could it maybe have been running too rich at times on past trips where it would foul a plug for a few minutes at idle but then clear up and that’s what I was hearing with the light popping but then maybe this time if fouled it too bad that it didn’t recover? Thanks again