Just for my piece of mind more or less let's say some one IS reading this.
My blue blazer 2 door rear wheel drive with a engine i perched from e-bay
for $900.00 that is suppose to have only 37,000 miles on it is showing an
error code P0306. Yes i did read as meany post as i was able to find on the error code and even looked under flashing engine light . Yes i have changed
all the spark plugs with AC/deco $7.00 each they were all new before change
because i just doped a different engine in my blazer and wanted all new stuff to keep things like this from happening . All so got new cap rotor plug wires for the second time. no change. got lucky and still have not gotten around to getting rid of old motor and pulled the fuel spider out (after reading other people post thinks every body for this great body of knowledge!!!).
problem changed from P0306 to P0300. But my check engine light went off.
Well for a little wile . I was thinking i was in the clear it was Thanksgiving
and i had to drive 3 hours to see mom.I got up on the highway just fine was drive for about an hour at 65 mph was going good but was getting past by every body. So i speed up to 85 mph check engine light come on
and flashing (knowing this can be vary bad ) i slow down about to pull over and all the bad lights go clear truck sounds good no flashing check engine light no check engine light so i get backup to 65 for about 15 min.All good
i take it back to 85 the same thing starts all over.no prob ill just stick to 65 mph right? another hour go's and every thing looks good no lights come on so i pull over for coffee. when i come out and start the blazer the check engine light comes on i shut off the engine and check every thing i can think of and can not see a thing wrong and i do not have a engine reader
and no one is open on thanksgiving day that has one so it's not blinking i go
on to mom's. ran good 145 miles on a little over 1/4 of a tank. i think may i got 20 mpg? (is this bad for a blazer?) (0h and my blazer has a sever right pull so I'm sure this did not help gas mileage). had dinner came home keeped it at 65 all the way the check engine light is still on.Ill have to get it read before i know more can this be an 02 problem?

 

20 mpg is normal for a blazer, and yes it very well could be a 02 sensor, but when you get the codes read it should tell you if it is an O2 sensor or not