sputtering problems?

so i'm not very mechanically inclined but i figure this is an easy fix..... we have a 4.3 MPI tahoe Q6

so we were on the lake last weekend and the boat started sputtering. it only did this while under part throttle...so coming in to dock, pulling boarders, etc. It wouldnt do it under full throttle. Also it would kill the engine every now and then when you come off the throttle after boarder goes down. I'm assuming i just need to change a fuel filter?

It was fresh gas but i havent put any fuel treatment in it for probably a year. u think i just need to drop some of that in there or go ahead and change fuel filter? it hasnt been serviced since the beginning of last summer

any help is appreciated, thnx!

Re: sputtering problems?

Change the filter and find out! But, when you take the old filter off, pour it's contents into a clear container and see if it has water in it, is so, tell us how much, be it a teaspoon full, shotglass full, 1/2, 3/4 of the contents etc. Doesn't have to be exhact. DO NOT try to reuse that filter as any dirt will end up on the wrong side of the filter.

Re: sputtering problems?

soooo, we switched out the fuel filter. there was prolly a little less than 2 shot glasses of water. we also put fuel treatment in it. it ran better, but it did have one little case of doing the same thing after about 3 hours. only did it that one time in the 5 hours we were there. the boat didnt seem to have quite the *** tho. not a huge difference, maybe like -20hp.

theres also a lot of water coming in and its not from the plug. we have to bilge about once an hour to keep it cleaned out. we figured this was from the plug but apparently not as we changed it out. once, again i'm not very mechanic so i dont know what to look for. think my block may be cracked?

Re: sputtering problems?

Pull the boat out of the water and run it on the hose. Leave the plug in and see if the boat fills up with water. I wouldn't thinks it's a cracked block with the motor running as well as it is. I'm no expert though! Was the boat winterized last year? Better guess would be the ujoint or shift cable bellows. Again with the boat out of water trim the drive all the way up and look under it for signs of holes cracks, roughness, etc in the rubber. If its been a while it's time to change them.

Re: sputtering problems?

Check the engine block & manifold drain cocks, maybe they're loose/open/worn out & leaking. Seems like if they were missing/open you'd be getting a lot more water than that, but they could be leaking. Maybe also check the gaskets around the risers. Look for water coming in from the transom around the outdrive (dunno, I don't have a Merc).

Re: sputtering problems?

it was not winterized as i live in east texas and didnt really figure i would need it. and then go figure we actually had one of our coldest winters down here and a couple freezes.

1 or 2 of my friends ended up with cracked blocks this year is why i ask. do these motors have a "freeze plug"? somebody told me if it has one then it might be blown and that its supposed to keep the block from cracking? kind of like a surge protector?

i'll try hooking a hose up in the next day or two and run it to see if we can see anything going on.

thnx again for any help

Re: sputtering problems?

I believe those "freeze plugs" are mislabeled & are more accurately casting plugs. From reading through these forums, they don't seem to do anything to save a block from cracking under freezing conditions. When water freezes, it expands in all directions. If it's freezing in places not near the plugs, it will crack the block/manifold. I'm no engine expert, but I wouldn't put any faith in those plugs keeping my block from cracking if things froze.

Re: sputtering problems?

There is an interesting thread in the adults only section about "freeze plugs." To make a long story short they really aren't freeze plugs. They are the holes used to hold the block in place during casting. Nevertheless they do tend to pop out if water in the block freezes. This really isn't anything to be comforted by since you have to pull the engine and have them pressed back in.

Re: sputtering problems?

They are actually from the cast process but not for holding the block in place. These holes are where the foundry pours the sand out of the passages after casting is done. they use silica sand in the form of the water and oil passages that attach to the outer mold then pour the iron in the mold. They let it cool down to a few hundred degrees then "break" the sand out. WAHLAH you have a rough engine block. The aluminum blocks are done the same way basicly.