Chrysler Repair: 3.3L Grand Caravan - Misfire on 2/5 cylinders, grand caravan, discrepency

Question
QUESTION: Thanks for your time.
I have been chasing an issue for a while and am stumped.
My van has a persistent misfire problem.  Code 43 comes up from MIL.  Code reader indicates either random or cyls 2/5.

Here is some history:
Recently changed (within 1 year):
plugs, wires, coilpack, cam posistion sensor, crank position sensor, fuel pump, fuel filter, MAP sensor

Present symptoms:
Had been running OK, but having code 43 more often than not being shown for several weeks.  Having changed most of the ignition system, was looking at vaccum leaks and fuel supply issues.  Solution still not found.

Friday had a no-start condition following very rough idle and very low power as driving with flashing MIL.  I supposed cause was fuel pump (1 week old!) which had been making a lot of noise. I replaced under part warranty.  After priming fuel rail and clearing codes, got it to start and ran nice. No codes.  Felt relieved.

After 1/2 hour drive home, engine coughed slightly, then progressively more misfire occuring especially noticable under load climbing hills.  Now it occationally will have a "pop" like sound that seems to come from the exhaust system.  Could be a small after fire.

In curiosity, I pulled plugs 2 (because of codes) and 6 (at random).  All are about 6 months old.  2 looked like it had thousands of miles on it-- not oily, but dark with rounded corners.  6 looked right nearly new.

Question is:
What am I missing?
Could this simply be poor plugs on cyls 2 and/or 5?
What else could be causing this?
I do not have a wiring diagram to check the wiring from coilpack to Computer for shorts, but harness appears in good order and properly routed.

I have placed big screwdriver on each injector to listen for activation.  All seem to work.

Any advice you can offer in solving this is appreciated.

ANSWER: Hi Stephen,
Because of the discrepency in the appearance of the two plugs my inclination with this history would be to do a compression test of all 6 cylinders to see if 2 or 5 might be low. You didn't mention the year or the mileage on the engine so I can't be sure about  wiring of the coil pack but 2 and 5 appear to be controlled by dark blue/yellow wire (k17) on pin 17 of the 60 way connector in '93 and '95, or pin 3 of the 40 way black connector (dark blue/tan wire) of the '98 model at the pcm's. (Those are the 3 manuals I own.)
If the compression is ok and you no longer get a fault code 43 then I would look for a faulty injector for the affected cylinder(s). Thanks for the complete history.
Roland

---------- FOLLOW-UP ----------

QUESTION: Thanks Roland,

To do the compression test, I have to tear things up as if changing the plugs and it puts me most of the way to changing the injectors, so I guess that is convienient.

The van is a 1997 grand caravan, has 220K miles on it.
I know... a lot of miles, but it uses NO oil at all unless I forget to occationally tighten the valve cover bolts or oils pan bolts.

The plugs that were installed were a brand that some mechanics have said were questionable (OEM brand)... they happened to be the less expensive option as well.

I'll likely replace all with better plugs.

Does it seem reasonable that since the drivability issue is intermittant... there are times that it runs well and the MIL goes off... that this is less likely the compression and more likely an injector (leaky or intermittantly functioning) that fries the plugs due to improper fuel delivery?

Thanks for your time and experiences

Answer
Hi Stephen,
Yes, the intermittancy does point toward something that is electrical rather than mechanical, and because it is confined to either or both 2 and 5 you might do well to see what the #5 plug is looking like when you pull it. You may just have a faulty injector on #2. Be vary careful when dealing with the fuel rail, it is delicate and very expensive to replace. Please let me know how things work out for you.
Roland