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| 5.8 Ford OMC runs rough at high rpms fine at 3/4 throttle ? https://www.smwebhead.com/phpBB3/viewtopic.php?f=21&t=12031 |
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| Author: | Mark T [ Tue Jul 23, 2013 1:43 pm ] |
| Post subject: | 5.8 Ford OMC runs rough at high rpms fine at 3/4 throttle ? |
My 1994 Four Winns Sundowner is running rough at higher RPM's 42-4800. It started over 4th of July weekend and seemed like it was only hitting 7 cylinders at high speed, but was fine at lower RPMs. I tried to check the plugs, but the stupid ass engineer put 6 of the 8 plugs buried in the manifold in such a way that the only way to get to them, was to take off the manifolds and I didn't want to do that if I didn't have to. I pulled the distributor cap off and noticed some burning and etching on the metal pieces on the cap, so I replaced that as well as the rotor. I also put 48 oz of Seafoam and about a quart of Lucas injector cleaner into about 55 gallons or so in the gas tank. Fired the boat up, sounded great, took if for a gentle cruise for a half hour and sounded great. parked the boat, cleaned up the bottom then headed back to St. Joe at 3/4 throttle and still the engine was as good as it has ever been. Put the throttle down full and within a few seconds, it was again sounding like it was missing. Throttled back and still missing, put it in neutral then back in gear and it was fine at mid speed. Do you think its the plugs or plug wires ? Headed up to Torch Lake this weekend and would love for the boat to run at higher speeds since Torch is so big 18.5 miles long and 2.5 wide. |
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| Author: | Walt [ Tue Jul 23, 2013 4:58 pm ] |
| Post subject: | Re: 5.8 Ford OMC runs rough at high rpms fine at 3/4 thrott |
I had the same on my merc 6.2 twice. First time was a bad plug wire at only 2 yrs old; second was the cap (for the same plug as before) the next season. Thus, I would change the plugs and wires. While you are at it, run a compression check, Easy enough to do, and if everything is OK, it at least gives you a baseline. Might not hurt to check your fuel filter/fuel pressure. Fuel starvation could be an issue at high load/RPM. |
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