2000 Jimmy misfire rich trim

Have 4.3 W eng 2000 Jimmy that has started acting out this month. (Figures since the inspection is due!!)
Originally got 0303 code, but lately get all 0300 codes.
Gets better when warmed up but still flashes check engine.
Stays on, stops flashing at low rpms.

Distributor, module inside , rotor, cap and wires replaced.
A little better.

Been reading different threads, but have couple of things for the grey hair in the crowd to decipher.

May have vacuum issues, heat comes out the a/c vents in all heater settings. Will check in the daylight tomorrow.

B2 short term fuel trim shows -.2.34 up to 18 % at various speed.
B1 shows 0 up 50% at various speeds.
i.e. B1 50% B2 4.69%

Also had good bit of water at exhaust pipe when cranking after sitting a few days in the cold.

I also see I need to borrow a fuel gauge and get a read on that.

Does any of this add up? Thanks!

If you have a missfire check for good spark to all plugs and fuel pressure.
Then have a lok at the spark plugs?
How is the plugs?
Like are they new AC delco plugs?
MT.

Update:
Had fuel pressure leakdown issues. Old Master coached me through that one.

At this point have the following:
Good spark on new AC delco plugs
New distributor, cap, rotor, module and wires.

Replaced lower intake gasket to get the water out of exhaust. (flushed pan , new oil and filter)

Now have MFI spider. 60 psi running, holds 55 psi long after shutoff.
Power much better at midrange and above.

Still getting P0300 mult misfires at idle.
Still get high B1 short trim. Aprox 40% while B2 runs in single digits.

Upstream B1 O2 sensor voltage was staying above .5 V but after driving some it runs between .2-.9 like the other bank (2). Acts like it had a coating or something that finally burnt off.

Guess I'll have to take somewhere to get cylinder misfire numbers. My unit won't see them.

Any of this make sense? Suggestions please?

Thanks John

Did you check/reset the camshaft retard setting on dist position?
When they are checking what cylinders are missing.
Have the also check for past and present and how many times each one is missing.
And watch and check the fuel trims.
Also check camshaft retard setting on the good scanner.
MT

Did you check/reset the camshaft retard setting on dist position?
When they are checking what cylinders are missing.
Have the also check for past and present and how many times each one is missing.
And watch and check the fuel trims.
Also check camshaft retard setting on the good scanner.
MT

Wasn't able to get to the shop with the good scanner today. Hope to on Monday.

I did check the vacuum. Running at idle steady 16 in hg.
Checked at intake with other hoses removed. about the same.
Advanced the dist one gear tooth. Picked up about an inch of hg (17)
Seems like it ought to run around 19-21, but not sure.
Spent a good bit of time looking for leaks.

When I rev engine slightly, of course the vacuum increases some to about 21 in hg. In the couple of seconds it takes to come back to 16 the engine smooths out before it starts rough idle again.
Don't know if its the mixture from reving it clearing out or having enough vacuum for a moment.

The short term fuel trim on B1 has been running up to 40 % while the B2 runs
+/- in single digits. One reason I thought might be a vacuum leak on left side of engine.

These machines are certainly an education.
Glad there are some good professors out there.

Any thoughts?

John