New here, got a 1995 Blazer 4.3L. Here's the problem, idles real rough, going down the road it bogs and backfires after it warms up. Sart it up cold it runs alot better, but still has a miss. I took it to AutoZone and the code reader gave me some codes: misfire on no. 4, random misfire, an oxygen sensor code, and some other oxygen sensor code (sorry left them in truck at parents). What I did, I put all new plugs, wires, cap and rotor. Also, put new oxygen sensor in. That didn't help, searching here I saw that the spider injector causes my a lot of problems. So, I pulled the upper intake and saw the washing on the passenger side, and said cool that must be my problem, after $300 for that problem still isn't fixed. Does not have any codes in it know I put a fuel pressure tester on it, 55 at idle and about 58 with key on, doesn't bleed off very much in a half hour. Put a vacuum gauge on it, I got 15in. at could start, after it runs for about 5 minutes the motor start shaking and vacuum drops down to 10in. Did a compression test on the no. 4 cylinder and got about 100psi or so.

Is there only 1 oxygen sensor on the 95s? I could only find one, right in front of the converter.

What I believe is wrong is a vacuum leak somewhere, but I'm not sure where to even start. I unplugged the two or three vacuum lines off the intake and vacuum stayed the same. Sorry for the lengthy first post, but this this thing is killing me!!! Any thoughts or ideas, please let me know.

 

Just an update did a complete compression test and got
#1 167
#2 160
#3 167
#4 130
#5 170
#6 167

So, it looks like I either have a bad headgasket or a valve is bad. Any ideas on how to check for a bad valve under the valve cover.

 

Yeah, #4 looks low.

You could make your own fitting to pressurize the cylinder. Then look for bubbles in the radiator (headgasket) or listen for the sound of escaping air either from the oil fill tube (bad rings) or from the throttle body (valve).

You can also get a test for the coolant that will show byproducts of combustion.

 

Alright put air down into the cylinder, and it is defiantly coming out of the throttle body. So, it looks like a bad intake valve.

Do you think that this could cause all of the problems that I described in my first post?