2000 Safari has a bad miss...

[Dungeness]

Boy am I stumped! Here is a list of the things I have replaced on my AWD 2000 Safari 4.3 with 234Km while trying to get rid of a low speed hesitation which turned into a miss:

fuel filter
air cleaner
spark plugs
plug leads
coil
distributor (new, complete with cap, sensor, rotor)
mass airflow meter
fuel injection spider (inside plenum)
It still has a miss barely detectable at idle and high revs but pronounced off idle in neutral or drive.
compression test at 165 or better all cylinders
spark plugs look fine
It throws up a PO135 code sometimes after driving on the highway (O2 sensor)
Before FI replacement, fuel pressure would drop 1 psi per minute, after new spider, maybe 1/3 psi drop over 2 minutes
Since FI replacement, is putting up PO303 code (misfire cyl 3) (spider not crossed up, I checked)
tried new plug and wire in cyl #3 to no difference
all cylinders seem to act the same when removing individual leads at distributor cap while running
fuel pressure at 58 lbs (within 55 to 60 limit)
no detectable sparks at night
is cam rounding off?
is new FI faulty?
is some other sensor faulty?
is wiring harness faulty?
is engine computer going bad?
????
My best guess is new FI is faulty since the PO303 code started then, but maybe disturbing the wiring?

Any suggestions would certainly be welcome. Thanks everyone!

[Captn. Crunch]

Dungeness
I see nobody has come to your aid on this and I think I know why. It looks like you've already done everything anyone could think of doing. Electicity is funny stuff and ive only got a couple of left field ideas. Did you use a spray bottle to mist water over the wiring? Also find and clean any ground straps

[AstroWill]

I would start with a compression check.

[Dungeness]

Hi everyone,

Thanks for your suggestions, as it turns out, the injection unit I installed was faulty and replacement made the codes go away and it ran the same as before, with a noticeable miss. I misted the coil to no avail and then replaced the plastic protectors on the plug leads for the left bank where they come out of the distributor. Looks like the new leads were touching the metallic cowl lining. Low and behold, when I reinstalled the engine cover the miss was all but gone! There is still an occasional miss when cold but it appears that was the problem. I've replaced a lot of parts chasing this issue, I recommend a making sure all the plastic protectors on the plug leads are in place when first trying to find a miss on an Astro or Safari.

[Captn. Crunch]

Hey
Good job sticking with it and tracking it down. So that was a faulty injector spider rite out of the box? That's some frustrating stuff right there. Your trying to diagnose and your thinking " can't be that-its brand new". But we're seeing more and more of it as more and more parts are garbage made elsewhere.

[Dungeness]

That was one tricky miss to sort out! Despite all my replacements the miss just kept coming back so finally I gave up and brought it to a shop. Guess what? Even though it has only 250K the timing is worn enough that the computer can't compensate so we oblonged the distributor hold-down bolt hole enough to get the timing right and it has completely cured the miss.

Sure appreciate everyone's help and hope sharing my fix pays it forward to someone else in the same fix.