I have a 98 blazer with around 230k miles. It just developed a major misfire under load, worse when it’s cold. I’m not getting any codes to come up ( using dash command app on iPhone with extended Chevy parameters) I’m thinking at this point it’s vacuum or ignition. I replaced the plugs, distributor, and cap around 20-25k ago so plugs may be going bad. My brake booster has also been acting a bit odd to for several months so it could be that as well. I have had in the past codes for low catalyst efficiency bank 1 that kept going on and off, most recent code I got when the problem first started was a bank 2 rich fuel code. I have about 15 different things I can think of that could be causing the issue but don’t know how to diagnose without having more codes. I do have a video but don’t know how the quality would carry over to here to hear the problem

 

Just pulled the bank 2 sensor 2 o2 sensor and think I can rule out fuel and exhaust as causing the issue. I did get a code saying I had pulled the o2 sensor showing that they are working so if it was fuel or exhaust I should be getting codes for that which I’m not

 

Please check and report Cam Sensor Retard (GM.ENGINE.CMP_RTRD). General Tab of Data Grid/ADD PIDs.

 

I started it and it read -8.8°, slowly revved it to 4k and it went to -9.4° to -9.9° and basically stayed there with no load. The TPS is reading -0.8° at idle and about 12° at 4k with no load

 

I was able to log the misfire counters on dash command even without a check engine light code. All cylinders except 5&6 are misfiring badly. I’m thinking at this point a combination of bad plugs, wires, and a bad coil.

 

Cam sensor retard needs to be zero +/- 2 degrees to avoid misfires. This is very common problem. Rotor needs to orient to the terminals correctly or sparks can jump around where they shouldn't. Probably a worn distributor gear needs replaced. Timing chain slop showing up as excessive cam sensor sensor retard can be corrected by putting a SBC distributor hold down on and turning the distributor. Once you have cam sensor retard set correctly, then replace the cap/rotor with Delco units. (Timing is not set by turning distributor - it is determined by crank sensor and PCM.). So rotor needs pointing to right place when the spark comes through! Its the very first thing to verify when chasing down generic misfires on these.

 

I would really doubt it’s a distributor, I just replaced it less than 20k ago. As far as I know the distributor in the 4.3 vortec is fixed.

 

Fixed without basically removing the whole thing that is, I’m not equipped to do a distributor or timing anyway with what tools I have

 

OK then

 

I just figured I’d look into easy stuff before going all out and taking it to a shop🤷 my code reader has been wrong before on some of those PID as well. For whatever reason it was never able to get correct rpm from day one. If the coil, wires and plugs doesn’t fix it, I’ll be ahead a bit as they did need done and the cam retard would probably be where I would head next although I would probably want to investigate why it just went bad all at once. I was reading some older threads that said on the higher mileage vortec the cam can get excessive thrust which in that case I’m screwed because I do not have funds to pull an engine and tear it down