Heavy load "misfire" sounds?

[Mitch925 0]

So I am having a misfire issue as well. I have an 09 Avalanche C4 5.7. It idles fine but as soon I put a load to it. Maybe just accelerate to about 1100 - 1500 rpms it sputters and sounds like it runs hard and vibrates a lot. I don’t notice any thing with the trans and the prop looks fine. I just had a new cap and rotor and wires installed in October. I am going to change the spark plugs next. Is there anything else maintanence wise I can do before I start getting into testing the injectors. The motor only has 200hrs on it. 

Edited February 4, 2018 by Mitch925

[Troy 234]

Maybe coil. I'd start with the plugs though. when mine was acting like that the rotor and cap fixed it. 

[Wylie_Tunes 146]

On 2/3/2018 at 9:08 PM, Mitch925 said:

So I am having a misfire issue as well. I have an 09 Avalanche C4 5.7. It idles fine but as soon I put a load to it. Maybe just accelerate to about 1100 - 1500 rpms it sputters and sounds like it runs hard and vibrates a lot. I don’t notice any thing with the trans and the prop looks fine. I just had a new cap and rotor and wires installed in October. I am going to change the spark plugs next. Is there anything else maintanence wise I can do before I start getting into testing the injectors. The motor only has 200hrs on it. 

Was the cap, rotor and wires installed for this reason, or did this pop up after? If the later, then you have to go back an look close at the last work done. Are these quality marine products you used? Cheap ignition components dont last long. Yes, replace the plugs anyway. 

[Mitch925 0]

Yeah they are all quicksilver parts. And they were installed by a mercury certified repair shop. I’ll look at them this week. 

[Mrwick 65]

It doesn’t take long in a marine environment for a cheap/inferior ignition part to fail.....this is one of the few instances that I would recommend an OE part.  FYI....last year my boat had a terrible vibration and I thought I had prop problem.....after a careful inspection of the drive system, I didn’t find a problem......just by chance, I pulled the distributor cap to find the electrodes completely corroded up.....replaced it with a quicksilver cap and rotor because I couldn’t find an MSD marine version.....Problem solved.   Vibration gone and she had a lot more power as well!  The cap I took off was a one year old Sierra.