1995 Blazer - Dreaded P0300 Misfire Code
 

1995 Chevy Blazer - 4.3L V6 4x4

Original Problem: Started up great, but ran poor with poor gas mileage. O'Reilly Auto Parts pulled codes: ....the dreaded P0300 code.

What I have done:

Replaced Spark Plugs (NGK), Distributor Cap and Rotor (Genuine AC Delco) Replaced plug wires (AC Delco), replaced fuel filter. Sprayed entire can of SeaForm into intake. Added entire can of Seaform fuel injector cleaner into fuel tank. Added Lucas to new oil change. Sprayed ALL vacuum lines with Cleaner and no leaks found. Pulled battery cable for 15 minutes to reset SES light, light came back on within 10 minutes.

Now the problem is reversed: Hard starting, idles rough but goes down the road and the engine runs smooth, but still get really poor gas mileage. O'Reilly Auto Parts pulled codes again: ....still the dreaded P0300 code.

To my understanding the 1995 does not have a (Mass Air Flow Sensor) ?
(Could it be the MAP Sensor?)

Looking for a suggestion of Next Steps. Any Suggestions?

Thank you for any suggestions!

Checked fuel pressure?

And you are correct, no maf on 95. Map will usually idle and start fine, but fall on its face under load, when it goes bad

Possible fuel pressure regulator under the intake plenum.

Do a fuel pressure leak down test

Same problem, went thru same steps. Replaced cat converter, now fun’s like new.