Our bone stock 96 blazer 4x4 is acting up, 96K miles and in excellent condition. What is happening is at highway speeds the engine will intermittantly loose rpms and then surge back up, and the tach actually swings up and down 500 and up RPM each way. Does this for a few seconds, then goes away, then comes back sometime later. The engine doesnt feel like it is dropping a cylinder, and no OBDII codes are set. I tried running in 3rd gear rather than overdrive and no help there, still does it. I will be doing plugs,wires, cap, and rotor tomorrow but feel this may be a sensor issue. Anything I can clean or look at? Can I clean the sensor in the air intake with anything (MAF sensor if that is what it is?) Anyone have any ideas? Truck feels like a bucking bronco and I really want to fix it. Thanks for any suggestions!

Clogged convertor-period..been there done that..went thru this with that with my wifes 94 Blazer w/a 4.3 Vortech..hope this helps smile.gif

when you have the cap and rotor off look at the distributor where the pickup coil is and see if the center shaft magnet pointers have cracks where the rivets go through, this will be the part that rotates. i have had this problem twice and will really through things out of time.

Thanks guys,
Heading out to the parts store now..planned on doing this today but other things have come up that may keep me until monday. Chris, how did you find out the converter was plugged? Any way I can check it?

Intake gasket between the upper and lower intake plenum.

Leo,
would that create a vacuum leak, something I can find with a propane torch? I did the intake manifold gaskets on the truck last summer because of a coolant leak, and it has run fine up till about a month ago. I replaced the oring seal between the two halfs but will give it a retightening just in case. Truck was due for a tuneup so I dont mind buying the regular parts but dont want to replace the catalytic if I dont have to. I have an xray OBDII scanner but dont know if it will scan realtime while the engine is running. No codes are set so not sure what I should be looking for anyway :(

Yes it will create a vacuum leak and I am told it will surge like you have with your Blazer. I don't know if you could find it with a propane torch, certainly wouldn't hurt to try.

thanks for the tips guys, think I have it fixed. Did the tuneup, plugs (couldnt get to the #3 plug, what do you have to do, remove the steering column??) wires, cap, rotor..test drive showed no change, but actually this was the first time I had driven it and experienced the problem. Its my wifes blazer and I only saw the problem from the passenger seat, when driving it seemed the problem was the torque converter was locking/unlocking causing the surge. Checked the trans fluid and it was down almost 2qt, topped it off and now all seems well. My fault, I havent checked it in quite awhile. I will know for sure once she drives it, but I am hoping that is it.