Hesitation under 3/4 to full throttle

[00stingray190rs]

Hey guys have an issue wth my 4.3 FI motor. It hesitates when I give it 3/4 to full throttle. I can feel the boat jerking somewhat and the rpms bouncing a little. The motor makes unusual sound also. I tried looking for similar problems but they were all carbureted. Any ideas?

 

[rbevis]

Re: Hesitation under 3/4 to full throttle

clogged fuel filters can cause hesitation. worn out fuel pump as well.

 

[Todd157k]

Re: Hesitation under 3/4 to full throttle

With FI, there are several things that can cause that:
1) dirty/clogged injectors.
2) inconsistent fuel pressure
3) inconsistent supply voltage
4) vacuum leak(s)

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

Ok Ill try and change the filter this weekend and should I run gym out or Lucas for the injectors?

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

ok so I changed the fuel filter and ran some gum out complete fuel system cleaner and still doing the same thing. When I give it good throttle it makes like a thumping rattling sound from the engine bay. I cant place where its coming from. I ran the boat for a hour straight at 3500rpm then headed back I gunned it and the sound/hesition happened. At idle or cruising the thing runs like a champ no issues sounds or anything. Any more ideas?

 

[EMC 1810SS]

Re: Hesitation under 3/4 to full throttle

Does it sound like your dropping marbles in a coffee can perhaps?

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

yeah i guess you could say that.

 

[EMC 1810SS]

Re: Hesitation under 3/4 to full throttle

That sounds like pre ignition which could be from high under hatch temps, wrong spark plugs, advanced timeing, or even carbon build up on the exaust valves.

Is your lake water warmer than normal?

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

I actually run it in our river which is quite chilly year round.

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

You dont think it has to do with my outdrive at all do you?

 

[EMC 1810SS]

Re: Hesitation under 3/4 to full throttle

Without actually hearing it I cant say. There is a HUGE subjectiveness in describing and interpreting sounds without hearing them

 

[liquidwrench]

Re: Hesitation under 3/4 to full throttle

Is higher octane alcohol free gas available to use? Might help if your fuel isn't that good.

 

[00stingray190rs]

Re: Hesitation under 3/4 to full throttle

I actually run a 93 octane in it all the time but its mostly ethanol when I do.

 

[Yellow Yota]

Re: Hesitation under 3/4 to full throttle

I'd suggest taking it to a shop that can hook up to your diagnostic port before you continue to throw money and parts at it. While none of the suggestions mentioned are bad, you might be able to pin point the problem with a simple diagnoses.

I had a similar problem. I cleaned everything, replaced the fuel filter, spark plugs, distributer cap, rotor, and a couple of other little things. Searched here, and got the most suggestions to look at my IAC. I did. It was a little dirty, but was not the problem.
I finally got tired of chasing my tail and took it in for a check. TPS voltage was all over the board. $38 replacement part and has ran flawlessly since I replaced it. Not a single person here posted a suggestion to check the TPS.
I'm not implying the people here gave bad advice. All of the other stuff was periodical maintenance items, but were still operating just fine.
Not saying that you need the same part. Just saying that the problem might be an easy fix. Before you start going nuts, might check into a diagnoses.