I bought a blazer today that doesn't run right, it has a rough running 4.3, barely stays running on idle. I hooked up my tech 2 scan tool and seen a bunch of codes, map, mass air flow, misfire etc, I then cleared all codes and started it up a few times with only the misfire code returning, it runs but ruff, It will barely stay idling and wants to die but stays running for the most part. I pulled up the misfire graph and cylinder 5 is misfiring constantly across the graph with 3 following behind very slowly... not nearly as bad (The guy that owned it before me gave it a full tune up, wires and plugs, cap, rotor and map sensor before giving up.) those are the only two cylinders that have misfire data, I disabled the fuel injector for 5 with the tech 2 and there was no change in rpm or the way it was running so I figured it was an injector or spider injection problem. I didn't mess with 3, had to leave for work, I only looked at it for about 10 minutes so far... had limited time working on this since i had to get to work. I've heard the spider injection on these motors are notorious for problems and was thinking it is a fuel injector but have a feeling it could be a cam or crank shaft sensor. from reading other peoples posts. I don't hear a vacuum leak and seen decent intake air flow on the tech 2 so i took MAF and intake gasket out of the equation, although that would make sense why the two cylinders next to each other are showing the problem... It sustains a hiccuping steady rpm with 1/4 throttle for a few seconds and then it seems to get confused or trys to compensate and starts dying down... sometimes staying at 1/4 longer??? I have to play with the throttle a tiny bit and bring it back to 1/4 for it to sustain again. does anyone have any suggestions on what the problem seems to point to more than others?

According to the Tech 2 the Engine is running constantly rich and not changing between rich and lean like it is suppose to. (I'm not 100% if I was in closed loop or open loop but thought reguardless it should variate between the two even if I was still in open)

I haven't been able to check fuel pressure or pull the #5 spark plug yet.

I know I have bits and pieces of information but I have only had time to look at it very briefly and am at work now.

TPS reading worked from 0 - 100%

 

ended up finding no compression in #5, pulled head, bent valve and broken pushrod, replace head with junk yard head and she runs great...

 

Thanks for the follow up! Glad you got it fixed!