bonesmalon

iTrader: (1)

Ok so starboard is not pulling as hard as port when at 4700 and up to 5400 with equal trim settings. Keeping in mind the starboard runs the power steering pump.
Pulled all 8 spark plugs clearly #6 is crappy. Looks like a cold plug would. looked fuely (I made that one up but you get the idea) Other 7 are perfect. First action was to put new Iridium plugs in as a direct replacement from NGK. Put about 45 minutes run time (20% WOT, 40% 4k rpm, rest is idle time) and #6 stood out again as not burnning clean when compared against condition of #4 and #2
Header pressure tested at 47 psi using digital pressure gage capable of indicating to 1/100 psig. Pressurized to 47 psig, hold for 15 minutes to allow heat-of-pressurization to stabilize, close off supply and monitor gage for 30 minutes...zero pressure decay.
Standard compression test yields 140-145 psig.
Cylinder leakdown cyl #6 2 psi drop (3%), #4 2 psi drop (3%), #2 3.5 psi drop (5.8%) didn't bother with #8
Plug wire specs are 1000 ohms per inch max. #6 wire about 30 inches long (30k ohms max allowable) measured 14.7k ohms and #2 17k ohms which is about 36 inches.

Possible contributors left to investigate:
#6 fuel injector (not too keen on having to pull the plenum and fuel rail and at $250 a pop guessing would suck)
Coil pack - any way to test without pulling as mine is right under transom ( others suggested swapping between motors but refuse to mess with port as it's running perfect)
#6 rocker arm wear/adjustment (a friend with 525EFIs has been down that road with rocker nut loosening up. Anybody else see this?) Ordered new header and collector gaskets to investigate this next unless I get a good lead on an alternative path of investigation.
Plug wire although meeting resistance spec might have leakage to ground path and spark is getting blown out at high RPM (course you can't buy a single wire to try it Set is $150ish local MOPAR motor guru at work after reading the plugs believes this is the culprit. He is suggesting I take one of the good used plugs and close the gap to reduce energy need to light the cylinder and see what happens

4mulafastech

Maybe swap #6 and #2 plug wires and see if the problem follows the wire. Same with coil.

bonesmalon

iTrader: (1)

Yup...that's the kind of logical thinking I want from the group. I'm not gonna just start buying parts without having some logical basis for it. Definitely gonna try that because routing the wires across the back should it prove to be the wire(s) is gonna suck. I have enough slack in 6 to get up to 2 or 4. Thanks additional input welcomed

Native Engines

After u put new plugs in it and ran it u said u pulled em out and it looked fuely ?? Did it look the same as when u took it outa the box?? Like it never burned?? If it did its probably an injector.

bonesmalon

iTrader: (1)

No when I checked it #2 and #4 looked barely used, 6 looked fuely, center ceramic was brown like it had residue on it.

Kelly O

Just went through a similar situation, ended up finding a bad coil. Surprised how well it ran on 7 cylinders, could not really tell- it was only down 200 rpm to the healthy motor but felt sluggish.

Our ignitions are different, but I would swap coil pack from your healthy motor and see if problem follows.

bonesmalon

iTrader: (1)

Thanks for the input Kelly. Plan to swap #4 and #6 plug wire at both ends and have clean plugs in both to see if the problem follows the wire. If it doesn't the coil is the next place I'm going. I saw a thread that someone else had a coil pack with small cracks in it. The damn coils are way at the back of the motor directly under the lowest part of the transom edge.so when you see me and the backs of my hands are all chpped up you'll know I decided to change out a coil.

If I'm not rnning along side you this weekend you'll know I haven't solved the problem ;-)

KWright

If you need one plug wire let me know the length and I can help you out.

bonesmalon

iTrader: (1)

Thanks! After I do the wire swap to see if the problem follows the wire I might take you up on that.

SS496

I dont know how much access you have.... but a quick easy check for spark leakage is spraying the suspect high voltage leads with water out of a spray bottle (on a running engine). Works well for finding arcing out plug wires, coils, distributor caps (i know you dont have one in this instance), etc.

Easy cheap and effective, however this will only test for spark leakage and will not totally rule out the suspect/failing internally coil. I would recommend the spray down first then moving on to swapping parts around to see if the issue follows.