I have a 99 blazer 4x4 4 door. First of here's the issues. I can not get 4x4 to engage after the transfer case I get no bliking lights or anything and actuator seems to have suction but wont engage, iv changed the transfer case vaccum switch and the electric switch upfront. Second issue is when the a/c is on depending on the location I want air to come from like floor or windshield, heat comes out. Third issue is ONLY in reverse often but not always when I back up my brake pedal will go to the floor and the brake light on the dash will come on signifying an error. As soon as I put it back in drive and oump my pedal pressure back up I have brakes, light goes off and its fine. Only in reverse it doea this, fourth is I had acceleration issues so I changed my regulator and it fixed 90% of the issue, now when I hqve to go into passing gear for an extended amount of time , like going on the on ramp to a highway at as soon as my blazer hits 70mph it seems to lose all power and just steadys out and wont go any quicker, like it struggles for power. Ill let off and cost for 10 to 15 seconds and go into passing gear again and it will go right past 70 no problem. In the time all this is happening I usually get a random multiple cylinder misfire. Someone said all of this could be entirely caused by a vaccum issue, I'm completely lost and could use any help given at this point. Thanks in advance for any help.

 

Sounds like the problem is related to vacuum like you said, although im not sure about the brake issue. What does your truck idle at when its warm? Also, while its idling can you open the hood and hear a sucking noise? indicating vacuum leak. More often than not, misfires are caused by faulty ignition parts but vacuum can cause a misfire symptom i believe.

 

it idles at about 650 to 700 rpm, that i can remember i don't think i can hear any sucking noise under the hood. its all very confusing.

 

So you changed the fuel pressure regulator? Or are you talking about the distributor cap? Have you checked the timing? Cleaned the MAF sensor? When was the last time it had a tune up?
To check for vaccum leaks spray some brake cleaner around the throttle body with it runing. If the idle changes, you found the leak.
Have you checked to see if the 4x4 actuator cable is free? Are there any lights on the selector switch at all? May be just a bad selector switch.

 

Yes I changed the regulator, cap, timeing is fine, automatic. Iv cleaned MAF, new plugs, wires, cap and rotor within last 3 to 4 months. The 4x4 actuator cable is free, no lights blink in error. Everything engages except actuator, iv had someone watch to.see if it moves and it doant.

 

I'm thinking that you may actually have multiple problems but one of them is likely to involve vacuum.
One thing to check is a vacuum hose that goes from the intake manifold to a connector near the master cylinder. It's known to collapse and crack, something that you can really only observe while the engine is running.
When you mentioned the reverse issue, I immediately thought about a case with a Jimmy that I encountered. It had rear drums. That truck had been driven hard and was a little low on brake fluid. Drum brakes only adjust themselves whenever they're used in reverse. To make a long story short, I topped off the brake fluid and made a series of stops in reverse. Whether I did the right thing (or solved the underlying problem) or not, I may never know... I do know that the brake light stopped coming on.