My 2000 Chevy express van make a funny sound only when I accelerate. And number 4 and 6 spark plug misfires

ECM may require a CKP relearn. Use of scanner required.

the high humidity (water) is attacking your electrical starting system, whens the last time you changed your spark plug wires , distributor cap & rotor ? how about your fuel & air filters ? cleaned your battery terminals ? try it , it will help !!!!!!!!!

No, the catalytic convertor does NOT sound right.
Normally with a random misfire a tune up takes care of it. What has also caused a misfire on those early motors is the popet injectors. They were prone to having problems and have been updated back around 2000 or so. But usually its a cyclinder or two or three or... misfire. All popets going bad is unlikely.
Might try changing the fuel filter and maybe checking pressure. Just the key on pressure should be 60-66psi. While running it may be around 60 and a snap of the throttle will make it rise to 65 or so.

Was it running that way before tune up ? If not you have a loose spark plug wire or plug.Make sure the plug wires are not touching each other or any part of manifold this could lead to spark jumping. You could even have a wire crossed. It could be a TPS ( throttle positioning sensor) I hope this helps

Start with fuel system. Listen for fuel pump humm at fuel tank No humm check wiring to pump for power. Then check for spark at plugs and wires. Remove wire from coil and hold near engine and see arch when you crank. No arch. Replace ignition Modular inside distributor cap or cap or rotor

I sincerely apologize for the late response...Due to the bad economic situation this site has had a substantial (+50%) increase in the number of questions being asked in the last four months.

I am not sure if you have the 1/2, 3/4 or 1-Ton model.
Also Not sure if you have the 4.3L, 5.0L, 5.7L or 7.0L Engine. However I have included all below.

For the 4.3L (6cylinders):
Firing Order:
1-6-5-4-3-2
Cylinders:
6------------5
4------------3
2------------1
(front of vehicle)
Distributor:
coil wire-->
-----6------->............<--------5-------
-----4------->............<--------1-------
-----2------->............<--------3-------
............(front of vehicle)

For the 5.0L AND 5.7L AND 7.0L (8-cylinders):
Firing Order:
1-8-4-3-6-5-7-2
Cylinders:
8-----------7
6-----------5
4-----------3
2-----------1
(front of vehicle)
Distributor:
coil wire-->
-----6------->............<--------5-------
-----4------->............<--------3-------
-----2------->............<--------7-------
-----8------->............<--------1-------
............(front of vehicle)


Let me know if this helped, or if you have additional information or questions. Feel free to contact me at FixYa.com!

The cylinder 7 misfire is likely a symptom of the problem, not the problem itself.

Typically, the catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream 02 sensor reading should be fairly steady. Typically the P0420 code triggers the check engine light if the readings of the two sensors are similar. This is indicative of (among other things - such as faulty sensors in the "emissions loop") a converter that is not working as efficiently as it should be.

I do not believe that it is a problem with a valve/head gasket or cam.

You should definitely replace the fuel filter though this probably won't fix your hesitation. It wouldn't hurt to replace the spark plugs this is usually the culprit on these engine. I have the same engine in a '99 caravan and found the for some reason the spark plugs on cylinder 3 and 4 loosen up after one year and cause a misfire between 45 and 50 mph under load (when mildly accelerating).

#1 plug is the 1st plug on passenger side by firewall

i have a 2000 Chevy van where is the fuse for the two(2) rear power outlets