Ok so I've taken my 2002 Chevy blazer to many mechanics and no one can seem to figure out what is going on with my blazer.

When I'm driving normally everything is fine, but when I go above 70mph OR when I'm going up a hill the SES light starts flashing and I can feel the blazer kind of stall a little or just jump a little and it seems like I have to give it more gas to keep going at the speed I was going. As soon as I get off the hill or slow down, the SES light stops blinking and turns off and everything is back to normal. I've had the code checked and they say it's an engine misfire code, P 030 or something like that. It's just one cylinder apparently. So I changed the plugs, wires, cap and rotor, and I even replaced the distributor. It still does this though. PLEASE HELP!!!!! I don't know what else to do, and I really really love my blazer. It's my baby and it has sentimental value, I don't want to get rid of it. Thanks for reading

 

Sounds like you are in need of a new fuel spider to me. Do a fuel pressure and leakdown test and report back with your results.

Also curious was your cam retard properly adjusted after installing the new distributor?

 

agree with rex, also, fire your mechanics

 

Take it and get the codes read. Even if the light goes off, there will still be DTCs stored. Get them all and write them all down. In the USA, O'Reilly Auto Parts will read all your codes for free.

There is a huge difference between P0300 Random/multiple misfires and P030x (where x is between 1 and 6) which is/are specific cylinder misfires.

If you have a single cylinder misfire, it might be a single injector failing in the spider, it might be the wiring to that single injector. However, it could also be a bad spark plug wire, a spark plug wire grounding out where it's touching metal, arcing in the spark plug boot (indicated by traces on the insulator of the spark plug), a worn spark plug, or a spark plug that's gapped too wide. It could also be an issue with the distributor cap post for that cylinder, look inside the cap for any problems on the post for that specific cylinder. Closely inspect everything in the ignition system related to the specific cylinder that's misfiring. Make sure the spark plug is gapped properly. Make sure the spark plug insulator is clean (clean it with mineral spirits or acetone and a clean cloth), and make sure you fill the boot on the spark plug wire with dielectric grease before pushing the wire all the way on.

BTW, if it's P0303, and you had a shop of questionable reputation change the spark plugs, it's highly likely that the #3 spark plug wasn't changed. That one can be a bear to change unless you have the right swivel/universal spark plug socket. I've seen S10 pickups with >150K miles with the original factory plug in that cylinder because nobody ever bothered to change it.

What's the CMP Retard angle/ CMP offset angle. If that's off, it can cause misfiring under specific load conditions, although that usually causes misfires on more than just one cylinder.

Fuel pressure issues, bad fuel pressure regulator and general issues with the fuel injector assembly (spider) tend to cause misfires on multiple cylinders rather than a single cylinder misfire.