2004 6.2 mpi runs rough, inconsistant knock sound/stumble between 2000-2800rpms

[stang32]

the engine ran great at the beginning of the season but one day ,the vacuum line came off the pcv and cause the engine to race . i zip tied it back in place and did a tune up. cap, rotor, wires, plugs. the boat ran great, then the next time it was used, it would not start without opening up the throttle over 1/2 way. this went on several times, i changed the IAC and muffler. the starting issue is still there inconsistantly but now for the reason for the post, the engine shakes when trying to get up on plane. from 1800-2800 i can watch the engine fuel filter shake violently . i also see the windshield frame shaking a lot. on top of this , there is a knock, thump heard in the back end, which seems to be more closer to the outdrive than the engine. the engine does slightly stumble when the sound is heard. but it is not a typical timed noise, it could be heard after 3 seconds, then 20, then 2, then 40, etc.
i hooked up the scanner to it and got 5 active (bull**** ) codes . 94-75-119-104-130. which all appear to be for sensors not used on this boat. the noise i hear reminds me of waves crashing against the hull. very frustrating. this boat ran excellent now, not

 

[alldodge]

Have you done a compression test?

 

[Fun Times]

Are you able to hear/notice any of these symptoms while on the trailer at home or does it have to be in the water?

What's your theory of why the PCV valve hose came off all of a sudden? Was someone working in that area lately that could of compromised the area ?
How does everything look in that area? Any buildup of oil, etc. helping to make the hose pop off, the valve still seem to shake out okay?

For starters I'd consider putting the old distributor cap back on to see if it helps with getting things back to normal....These design of flat caps can be troubleshooting nightmare...Even new ones.

Also check your spark plugs to see if they aren't damaged or fouled, etc.... Plus it sounds like it's time to perform an engine cylinder compression test so you know it's overall status.

May as well check your fuel filter for water/debris and test your fuel pressure too.

 

[stang32]

i was not on the boat when the pcv hose came off but i am kind of thinking it may have backfired and blew it off, which may have been a precursor to the issues i am dealing with now.the boat is in the water for the season, the noise is under load so even if it were on the trailer, i would not attempt to test it . the cap is a new AC delco cap and for what it cost, it better be good, the old one is long gone. the plugs are new with the cap/rotor, wires. the old ones were not bad but due for a change.

 

[scoflaw]

Fuel problems won't throw a code, and it sounds like you have one. That wave slap is a misfire. I would clean that fuel system from 1 end to the other. 15 year old injectors definitely should be serviced. Do the compression/leakdown to eliminate a valve problem

 

[alldodge]

While it might be a valve issue, but could also be the crankshaft position sensor. Assuming your using smartcraft monitor to read codes. Need a scanner or scanner software to and watch the timing see if it changes

 

[Fun Times]

It's good the boats in the water for this type of testing as it just makes things easier to help ensure you're heading in the right direction for proper repairs.

You theory of the PCV seems valid to your situation which is helpful to get you headed in a direction to stat with.

Bear in mind you just did a lot of ignition type parts changes all of which could have an effect of what you're describing plus going on when this new to you issue seemed to have accrue not long after a parts change was done correct?

The material used in some of these flat caps are important and prone to make these engines run like you describe so please don't let cost or brand be a deterrent though AC-Delco caps are generally good, there have been some issues with them in the past requiring them to make some changes....At the very least inspect the cap for proper installation by way of physical removal as they can be installed at accidental odd angles cracking the plastic causing issues as that was recently reported being "a" cause. Plus over/under tightening the cap screws would affect operation... Also look for carbon tracking inside the cap as these caps tend to get firing mixed with the coil wire side/prongs....Triple check the firing order of the plug wires too.

The DISTRIBUTOR CAP is often subject to cracking, carbon tracking, oxidation and ionization, all causes of misfire and crossfire. One of the most important spots to check is the carbon contact, located in the inside center of the cap, which wears over time, requiring that the cap be replaced.

Hopefully it's not internal but a compression and leak down test may be needed to know for sure if you can't locate any of the new ignition parts as the cause. And as mentioned earlier you do need to know what the fuel pressure is at too.

Good luck.