wow were in the same ball park here, im having the same problem with my 98 blazer 4 door 2wd, i just had my truck diagnosed, they said it was a vacuum leak and dirty maf sensor that i cleaned very well i believe. and i had the 2 same codes, i replaced all the vacuum hoses but they showed me 1 i forgot, they also said i did a poor job of cleaning the maf but truck had good acceleration when i left but now its back to rough idle and the initial takeoff hesitation + if i floor it from the engine bay it will bog and backfire out the TB. are you getting this also?. if i figure this out i will surely post it here and hopfully you will do the same.

P.S. the cracks you are hearing. i hear them when i turn the truck off and its comming from behind or unernieth the radio compartment. and also at operating temp can you smell antifreeze?

 

You are trying to diagnose one problem but you have another symptom that is causing to go down the wrong road. The missing vacuum resevoir is the reason you heater /AC changes when you accelerate. The damper doors in the dash operate on vacuum. Whn the engine is idling or not under a real load, vacuum is high. this gets stored in the magic black ball. When your truck is under load, the engine vacuum drops. the magic black ball is what is storing the needed vacuum for the heater/ac to operate correctly. If you replace the resevoir, your heater issures will probably go away. unfortunately, it wont solve your engine perfomance issue.

Have you checked for a plugged cat converter? pull an O2 sensor from infront of the converter and see if that makes a difference.

Good luck!

 

funny thing is my a/c and heat controls work fine, im just geting the same accel and ses codes he is we seem to be in the same boat, also my 98 blazer dosnt have that black canister. were the vacuum T is it goes to the fender and another wire runs under the abs down towrds the headlight but i dont have 4x4, so were does that one lead to?

 

The 98 has a vacuum canister mounted inside the fender instead of the big black ball that hangs from the hood. I have both a 97 and 98. This was one of the minor differences between the two.

Im not even really trying to figure out the drivability issue that was originally discussed. I am just pointing out that the missing vacuum resevoir is creating a problem that is quite possibly confusing the real issue.

 

Have you used the code 171 and 174 troubleshooting guide on this forum? There are many things to check that could cause this. Most of them dont cost any money either!

 

Ive checked but tried all the ones on there but nothing has helped. So im going to get a new fuel pump when i get paid but im also trying to find all the vacuum lines so i can check them all. I started the truck today to hear a low knock on cold start. Dosnt sound like lifters but sound was there for only 2-4 secs
hopfully not burnin anything up with it running lean

 

Sorry I forgot to mention I fixed the a/c problem by properly hooking up the vacuum ball, a/c and cracks are fixed but everything else remained the same.The light finally turned back on after about 4 days. How would I remove the o2 sensor?

 

An o2 socket or a large closed end wrench.

Why are you replacing the fuel pump?? Your first post stated you had 60 PSI and it dropped to 55 when shut down. I am afraid youre goint to be pretty ticked when the truck behaves the same way after spending $300 and 4 hours on your back!

The troubleshooting guide clearly states if you have the same pressures that you have, the pump is good!

Have you hook a scanner to the truck to do a live data stream? (Its cheaper than a fuel pump and can be used again and again!)

 

im the one replacing the fuel pump. primed its 53psi running about 47psi. pressure dropped more after i changed out a very bad fuel filter. i could here the filter shaking inside. and the fuel level goes haywire when i put it into N. juanfpina is having a vac problem and im havin the same problems he is besides my fuel pressure is low his is normal..

 

Sorry, i got the two of you confused. Im curious why the fuel pressure dropped with a good filter. Youre checking at the shrader up at the engine right? Not before the filter?

It sounds like juan has his vac issue resolved. Now he is just dealing with poor economy and drivability. Could be several things. But checking vacuum is a good start. Im not sure a vacuum leak could cause all the issues he is discribing though.