I am getting p0300. Random misfire. 2000 2wd blazer 260k. It misses when I have gotten up to speed on the interstate and the load has decreased. I am getting almost 20 mpg. Yet smells a little rich. Cat was removed by po.
. I po installed new cap rotor and wires. I removed cap and played with rotor. There is a few thou. Play rotationally and it does pull up an 1/8th or so.
is it time for a distributor?
skip white ok?
pic of truck.

 

pic of my truck

 

Anything else but P0300? A rich smell w/o cat is hard to take If You could drop here the O2 readings that would be easier for further troubleshooting. I'm not trying to play an expert here, but the info is too brief for me to guess. We could start from a plugs through the ignition coil and end up on a shafts sensors...

 

no other codes. i installed rear o2 into "anti fouler " this eliminated the "catalyst code".
here are pictires of B1o2 sensor.

 

PCM is controlling the fuel mix in the photo. Cycles should be several times/sec when holding 2000 rpm in park (time axis is not labeled in the photo so can't tell).

Can you actually feel the misfire at speed, or are you just explaining a flashing SES light and P0300 code? If so, please describe speed and exactly what is observed/felt.

Diagnosis will require a capable scanner. If you don't have a capable scanner get Car Gauge Pro (Android app) and the BAFX Bluetooth OBD2 adapter as sold on Amazon. If you have iPhone or iPad, get Dash Command + PIDs for your particular vehicle and find a Wifi OBD2 adapter of your choice (I have no recommendation there). These are both very inexpensive setups and will do a lot, however know that if you end up needing to do a crank sensor relearn this will require software like EFI live, Autoenginuity, or HP Tuners - or quite expensive dedicated scanners such as Snap-on or Tech2.

Test cam sensor retard and report please. Should be 0° ± 2° This will measure your rotor position relative to the terminal in the cap (a common source of actual misfires). I suspect the problem may lie here - but proof is in the testing.

Also, please check to ensure that misfire detection is functional and correct. Display misfire counters and pull plug wire to induce a miss. Counts on that cylinder (only) should rapidly increase. If not, the misfire detection system is not working correctly and the P0300 may be a false code. In the meantime don't disturb the crank sensor in any way (a common source of screwed up misfire detection systems).

Then get back to us.

 

i can feel the misfire it usually happens just after getting up to speed when load lessens. stumbles a bit then quits stumbling. it does not do it every day. it takes at least a mile of sporadic stumbling to trip light. then light will go off after next start up without stumble. there IS a miss. sometimes it feels like it misses a couple cylinders in a row.
which obd2 adapter? will any work?

 

just ordered This

 

I hope you don't have to do the Timing chain. mine had 200,000 on it and it needed replacing,a lot of slack. I experienced occasional surges or timing misses also. That wasn't the only thing it needed The rotor was out of time, the housing was loose on shaft due to catastrophic damage, so I replaced the distributor also. I had a sensor re-learn done. I am in the middle of dropping the trans. for a rebuild now I haven't tested it yet

 

the "miss" is only lasts a short time and goes away. it does not do it every warm up cycle.

 

If there is 260k on the OEM distributor I would suggest replacing it with one from Skip White. The OEM plastic housing distributors sure seem to wear-out the bushings long before 260K. They do come with new rotor and cap and I used them for a couple of months before installing GM cap and rotor, along with new wires. This was four+ years ago and been running great since.