I'm 99.9% sure I have a vacuum leak. Replaced the PCV valve and elbow as it was held together with tape, replace MAF sensor, check the fuel pressure, 60 and when it turns off after a couple of seconds drops to 55 which I believe is normal. What is making me believe that it is a vacuum leak is that when I am accelerating on the freeway, the a/c seems to be held back and blows out all at once when I release the accelerator.
It has rough idling, bad mpg, sluggish and hesitant when accelerating. Sometimes I cannot even go on the freeway because it won't go above 65mph. When I am going on the freeway, frequently I'll hear "cracks" in/under the windshield. Can anyone point me to common vacuum leak areas? I plan to spray it down with carb cleaner tonight and check the EGR as well tonight. Also I can't find where the vacuum ball connects, it's a 97' 2wd 4-door Blazer but I don't see any missing lines. Replaced the hood which is why I think I lost the line somehow.

 

I've got a 98 V6 and just fixed a vaccuum leak by replacing the line from the source of the vaccuum which is below the PCV valve housing. The other end goes to a tee at the driver's side firewall. From there it goes to my heater/AC controls and to my AT (I believe) which shifted hard before I replaced. Hope this helps.

 

I just changed that line as well but it made no difference. I had an old rotten line that was degrading to dust, and the tee is now connected just fine. The only thing that isn't connected is the ball under the hood, do you have that? Hard shifting is also another issue I have.

 

The only under hood lines I have are for my windshield washers and a wire to the engine compartment light. Have you capped one branch of the vaccuum at a time to see if anything changes in the engine performance?

 

I had a leak and it ended up being at the transfer case! Took forever to find.

 

I was suggested the capping idea by an autozone worker, but the problem is I don't know which lines are vacuum lines, and how exactly I would go to capping them. I don't want to damage something in the process so if someone could describe the procedure that'd be great. Before anyone suggests there is no sticker detailing the vacuum lines on the rad support, I swapped it with a junkyard one. Thanks guys! I don't think I have a transfer case because it's a 2WD

 

At the tee where you replaced the old line, take one of the branch lines off. For a couple of bucks you can get a variety of rubber caps to put on the end of the tee from which you removed a line. Run your engine and see if the performance is improved. If so, you've found your bad line. Now tracing it to the other end is another thing. If it runs toward the distributor and firewall, it is probably going to your climate controls. That's all I got, Good Luck!

 

The only one I could find was at the tee, the one that came from the pcv cover. I capped it and the ses light turned off but it continues to run the same. Any other lines I can cap?

 

Somebody correct me if I,m wrong, but it sounds like you capped the new line you installed to the vaccuum source and SES light went out but engine still running hard. It would be helpful to read the codes in your computer.

 

The codes are p0171 and p0174. Already replaced the MAF sensor, and checked fuel pressure. Light has stayed off for a couple of days, but still rough idle, loss in power, hesitation in acceleration and misfire, not always as bad but still there.