Seems that i have no luck with this blazer ! See if anyone knows what might this be. Running on a straight flat like and interstate or if going up a moderate hill the heater blows hard even on setting one . This is the kicker, I usually run just on the deforst BUT when the heater goes bazerk it blows out the vents that blow in your face ect. This lasts about ummmmm i dont know about 10-20 seconds something like that. Now while this is doing That the engine has a like a mis step or surge that drops 1 rpm and its pretty noticeable . Maybe this is 2 different problems but they seem to go with each outher.

 

The drop in rpm is the air conditioner coming on with the defrost, I dont know why the heater is coming on though, mine blows hot air out the vent all the time.

 

This sounds like you have a vacuum supply problem. Much of the HVAC system is controlled by engine vacuum.

 

That was my first thought but I cant find one, I did find a cracked small line going to the round canister attached to the hood and fixed itbut it didnt make a difference in how it runs, most of the problems I have had have been because of ignition problems, wires, plugs etc, they caused the same problem at the same rpm but I have replaced all the parts, I was thinking maybe the ignition module??? it can idle a little rough at times, not allways but it runs really well, lots of power, just that fluctuating at about 22000 rpms or at 65 mph, it drops off and then picks up over and over until I let off the gas and then power through the rough spot...really confusing!
I drive it for work about 200 miles a day and it is driving me crazy!
Do you know if it has 1 or 6 fuel injectors??? I cant locate any, as you know it's pretty tight in there! Thanks for your help! Brock

 

Brock, the CPI motor that is in your truck has one main electronic fuel injector and 6 individual pressure actuated poppet nozzles that are fed by the single electronic injector.

And who's truck are we working on here??? The OP has not yet responded on his problem... Are you helping him locally or??? Lets try to keep to one topic here.

 

I was thinking that there is a vacume problem also SOMEWERE. But i did find out that it doesn't seem to do the power surge, rpm loss when the heater is off....I havn't seen any lines off or cracks ect that i can tell anywere ....