This 1995 "W" vin Blazer has been a thorn in my side. New symptoms: Runs rough, with black smoke (I assume rich fuel mix) and vacuum at the dipstick and oil filler cap.

Just put new plugs/wires and distributor on it, new IAC, purge solenoid, EGR, PCV valves, TPS, Coil, knock sensors, CPS, replaced all vacuum lines, new 02 sensors. Basically throwing money at it in a local garage. Scoped the cylinders, they look clean (for 139k miles), compression tested fine in all cylinders, did bleed down test on fuel system, that's OK too. Timing is on, so I know it's not that.

My thought is an internal leak on the intake manifold (has been all along). Smoke test didn't indicate anything wrong. My only other thought is a plugged CAT.

These parts were replaced within the last 6 months, one at a time as codes came up. This time, NO CODES!

Any ideas?


I was told to pull the upstream O2 sensor out and see if it runs better. I guess bypassing the cat with the extra pressure going out the hole will tell me this?

I'm a mailman, so I beat my vehicles but maintenance is always first and foremost.

 

Just pulled the PVC out, covered it with my thumb and the problem with vacuum at the dipstick has gone away. Disconnected the IAC and no change to the rough idle. Must be something wrong in the intake or IAC. Last time the IAC problem only caused hesitation and near stalling when in reverse. Removed the CAT, no change to the crappy sputtering, so I doubt it's that now.

 

Figured it out finally. Just doing a followup, I don't have the vehicle anymore. The problem was the gasket on the upper intake. It was sealed fine on the outside, but was worn out inside. Got the problem fixed.

 

It would of been nice to see the fuel trims while this problem persisted , I bet they would have showed a vacuum leak. Thanks for the update.