Hey folks, I have a 94 model 4x4 with a 4.3 vortec that runs AWESOMELY. One exception - when it is above freezing & it is wet outside, it runs like crap and I smell un-burned gas. I suspect I have some ignition wire that is missing insulation that shorts out when it is wet outside causing some of the cylinders to not get spark. I know when this happens, it runs like crap & sucks gas like nothing else. It is so cold outside, I dont want to get out there to fix it, so if anyone knows a good place to start looking so I can get it done fast, then please inform me. Just for the record, I did a serious tune up with upgrades less than a year ago. I put in NGK iridum plus, good wires, high flow air filter, removed the cat & put in a flowmaster 40 series mufler. There is no trouble light showing and again, when it is dry out, it runs great.

 

Wet weather problems are a clear sign that you have an ignition problem. Areas of concern are the wires, cap, and rotor.

 

To Kyle's note about cap, wires and plugs, I'd add that you only want to put Delco plugs in - the NGKs are great in Nissans and Toyotas, but you need Delco plugs in your Blazer.

 

On the later trucks, NGK plugs were used at some point in the factory. I have removed them from a few different s-series trucks and they looked good. There is much speculation about AC Delco and NGK in terms of who makes what for which company and then rebrands them. I am fairly confident that some AC Delco O2 sensors are in fact made by NGK, but branded for AC Delco. I would agree though that in terms of plugs, AC Delco plugs seem to be more consistent and longer life than most all others.