Ok here's what I'm having, recently especially when it rains, my blazer shifts kinda weird... not really shifting but it justfeels, you know that feeling when the car shifts between gears, and it does it between 0 and 45 mph... feels like gas isn'tkicking
I've recenlty had a fuel pump installed, and couple days later my check engine light came on and it was my O2 sensor, I didn't change it anda week later the light went off!!
Any suggestions?

 

I would take a look at your ignition components (cap, rotor and wires) real close like. Go out at night and mist the engine with water (spray bottle on a fine mist) with the engine running. If you see sparks jumping to ground, then you have bad wires.

When was the last time you did a tune up?

 

Back in octobor 07 I did everything rotor, cap, spark plugs andwires... changed my pcv valve and had a new fuel filter all done bydecember 07.
Tell you the truth, it feels a little bitthe same before I replaced my wires, plugs, cap and rotor!!
but why??

 

What brand of parts did you use?

I would pop the cap off and check for carbon trails on the pins inside as well as carbon buildup on the tip of the rotor. Being humidity dependant points a big finger at the ignition system.

 

a mechanic suggested that my cap could be lose or untightend right... I checked it today and it seems pretty tight to me, wires are all tightin places!!

 

Dude, I am having the exact same issues with my 01 Blazer, but the first time it was an intake valve I belive that they replaced. My serpantine belt also looked pretty warn down so that also got replaced. I do remember hitting one puddle on a rainy day on this ****ty road near my house but since that its in to the shop 2-3 times. Also one of the times it went there it was an O2 sensor they replaced. It just came back on last week then went off and it came back on today on my way home from work.

 

I also have the same issue. I think It's pretty common for these. I have a 96 4x4

 

It could mean that the new parts are defective. I think that's what Kyle was getting at without saying it directly. You see, this is always a possibility. Just because you replaced something doesn't mean the new parts are good. If I were you, I'd do the test Kyle mentioned to eliminate the wires as the problem. If you don't find a bad wire, then your cap may be defective. I don't know how to test this, but I'm sure somebody on here does. Hopefully they will answer.

A lot of people on here suggest only using AC Delco parts for ignition components. Hope this helps.

 

One thing that has cropped up from time to time here is a plugged screen at the bottom of the distributor that may cause condensation under the cap. If this is the case, then it really wouldn't matter what you are using for ignition components as your misfire could be happening inside the cap given the right conditions. Something else to look into.

 

I would definitely put this screen on the 'usual suspects' list.