2005 226 with ZR6 stuttering under load

[SkiNautique2001]

I have a 2005 226 with 430 hours that gets used regularly. I just bought it 2 years ago, and this is the first year that it has lived on a dock. I've decided to leave it on the lift all year with two heaters in the engine compartment. It has performed flawlessly all summer, but 3 weeks ago, I dropped her in the water for a cruise, and it was stuttering under a load. She was fine at 20 MPH, but under acceleration or at speeds faster than 20ish, there was a lot of hesitation. The boat stays on a lift at a vacation home, so I can't work on it except for every few weeks when I'm there. I bought a new fuel filter hoping that was the problem and installed it today. The hesitation is still there. Is there a Schrader valve somewhere on the low pressure and high pressure fuel lines for me to check fuel pressure? If so, what are the specifications? What else should I be checking? The boat revs fine in neutral, but runs poorly at WOT. I also notice some backfiring if I slow from WOT to about 30 MPH and then hammer the throttle again. The backfiring occurs when I hammer the throttle to put it under load again.
The boat is stored about 1.5 hours away, so I would like to be overly prepared with parts and tools the next time I go up. What do you guys think?
Also, as a side note, I was reading about the pitot tube failures inside the gateway tonight on these boats. Can anyone tell me where the gateway is located on the 2005 226?

[d_nodixon]

I had the stuttering issue with my 06 210 ZR6...it ended up being the plug wires. I did not have the backfiring issue though. The stuttering issue was a gradual increase...I noticed a lack of power, when slammed to the gills, over a couple years then it eventually started stuttering.

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[SkiNautique2001]

The difference in my issue is that it started suddenly and has remained consistent since it started. It seems like it's starving for fuel, but I don't want to just start changing fuel pumps without knowing that is the problem.

[Quinner]

Have you checked the spark plugs?? If you are unsure when the last tune-up was done now would be the time to do it.

[SkiNautique2001]

I definitely have plugs on my list to replace when I go back up. I'm driving myself crazy spinning my wheels to find where to test the fuel pressures on the low side and high side though. According to the PCM manual, the threaded FCCs have a schrader valve on the top to measure fuel pressure, but the clamp styles do not. I have a clamp style FCC on the 2005. Am I correct in assuming that a tee fitting will have to be inserted on the high pressure fuel line just to measure fuel pressure? Also, I'm thinking that since the boat never stalls, the low pressure pump is less likely to be faulty than the high pressure fuel pump if this is a fuel delivery problem.

[Quinner]

Should have a valve on the fuel rail for pressure testing.
Have you traced the fuel lines back to the tank to confirm there is not an inline filter?? There should be a screen on the LPP, you could remove it to inspect/clean as required.
You could also inspect/clean the tank vent/line and also the anti-siphon valve, all could effect fuel flow if that is the issue.
Personally I would focus spark/tune first then look at the fuel related stuff.

[Miljack]

Have you inspected the screen in the FCC? If it's been a while that needs to be considered, especially with the ethanol content in fuel these days...

[SkiNautique2001]

I replaced the filter in the FCC, but I didn't notice a screen. I'm going to replace the plugs and wires in a couple of weeks when I go back. I was just hoping to take any other parts with me that have a high likelihood.

[Paxdad]

I replaced the filter in the FCC, but I didn't notice a screen. I'm going to replace the plugs and wires in a couple of weeks when I go back. I was just hoping to take any other parts with me that have a high likelihood.

Distributor cap and rotor.

[Quinner]

Distributor cap and rotor.

Don't believe the ZR-6 uses that technology

[d_nodixon]

There is a low pressure fuel filter also...I think that has the screen...you should download the parts manual, conviently here on PN, and you will see for sure

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[Miljack]

I should have said "filter" not screen in the FCC. Also make sure you dump whatever fuel is in the FCC when you take the bowl off. If you have water in the system, this could make the engine run as you have described.
Also, plugs and wires as somebody else here has mentioned.

[Laketexoma]

Long shot but on my ZR6 I had the same issue. It turns out that I had bad gas. Mine would start around 15mph. It would shudder and backfire. So how old is the gas in it?

[Ra140]

Did you manage to find the problem?

[DLafont]

Like Laketexoma suggested, seems like something water in the fuel may cause. How did the fuel look when you opened up the FCC?