496HO Problem

[HatenWinter]

I have this on Out Drive Tech but thought I'd throw it out here also and see if anyone else has any ideas:
OK here's my deal:
I put the boat in the water and it fires up fine, even seems to idle right. As soon as I leave the no wake zone and ease into the throttle it seams like its not firing on all 8 cylinders, no power, pretty much running like crap. The problem has been occurring for some time now. I finally get it up on plane and after a few minutes the rpms go up the motor smooths out and spead increases. All seams to go well from there. The problem does not occur for the rest of the day. The last time I put in was last week, I had the same problems but this time I just revved the motor up to about 3,000 rpms and after about 20 seconds it went away and ran fine.
I've had a code reader hooked up and it's not throwing any codes. It always seems to happen when the motor is cold. Especially the first run of the trip and each morning after it has sat all night. It never does it during the day when the motor is warm.
All maintenance has been done, pulled the plugs and they look good, and the fuel filter has been changed twice. I always use Chevron 87 gas and it never sits more than a few weeks in the tanks. The mechanic is unsure which way to go since there are no codes coming up.
Has anyone had a similar problem??? I need help, it's very frustrating!!!!

[lalhc]

I had the EXACT same problem the past couple of weeks. I told my mechanic that the motor was sluggish at times. He ran diagnostics and everything was OK. I thought that maybe I had some bad gas in the boat.

[SnakeWrench]

two things to look at. One, if the engine is lacking water pressure, it will stay at 3150 rpm until the water pressure either comes up or it will run like that until you replace the impeller. The other thing to look at along with that is exhaust temps. if one is way hotter than the other, (average is one will be 35 to 40 degrees hotter) the gaurdian will come on until the temps get closer together. The other thing, since you just had the filters changed is to make sure you don't have an air leak around the fuel filter or water seperating filter. 9/10 times, the water sep filter was over-tightened and has an o-ring leak.
How long is the idle out also and do you get any black soot on the transom. If you do, than it is likely the plugs are getting a bit fouled on the long idle out and it runs fine the rest of the day because the plugs clean back up.
None of these thing will set a solid code but will show guardian.
Laters
Snake

[HatenWinter]

two things to look at. One, if the engine is lacking water pressure, it will stay at 3150 rpm until the water pressure either comes up or it will run like that until you replace the impeller. The other thing to look at along with that is exhaust temps. if one is way hotter than the other, (average is one will be 35 to 40 degrees hotter) the gaurdian will come on until the temps get closer together. The other thing, since you just had the filters changed is to make sure you don't have an air leak around the fuel filter or water seperating filter. 9/10 times, the water sep filter was over-tightened and has an o-ring leak.
How long is the idle out also and do you get any black soot on the transom. If you do, than it is likely the plugs are getting a bit fouled on the long idle out and it runs fine the rest of the day because the plugs clean back up.
None of these thing will set a solid code but will show guardian.
Laters
Snake
Snake, thanks for the info! The empellor was changed back in May but I was still having these problems at the end of last season. It's possible that the housing needs replaced but the mechanic never mentioned it. I was also getting alot of soot on the transom. I don't have a H20 pressure gauge on the boat, just the H20 temp. It has never over heated but a couple trips ago the guardian did activate (ran through some sand). I pulled it out and had the code reader hooked up and it had 66 hits for low block pressure. The codes were removed, took it back out and ran like a charm, no soot on the transom. Next trip I had the same problems, but no codes came up this time.
As for the fuel filters, I do tend to overtighten them in fear of under tightening them. I'll take it off and re-seat it next trip. The idle out is very short at Windsor only about a minute. I usually have to wait a few minutes for the wife to walk down to the dock after launching before I get going though.
This sounds like it "could" be a combination of things.... :mad: :mad: :mad: