Yesterday while driving about 60-65mph the service engine soon light on my 2000 Blazer 4.3V6 4x4 w/106k came on and remained on for about 24 hours. As soon as it came on I had the code checked at Autozone. It was a code P0300 - Cylinder Misfire detected - Random cylinders. Possible causes: Plugs, wires, coil, vaccum leak, Injector fault, High or low fuel pressure. Planned to replace (as prescribed by local dealer service) Plugs, wires, pcv, and air filter since fuel filter and fuel pump were replaced this 4 days ago. Today the service engine soon light went away. The only change is premium fuel prior to SES light (not my choice). Otherwise the blazer idles smooth runs strong under acceleration but at steady speed tends to have very vague missing (hesitation) feeling around 60mph. Previous owner said "tuned up recently" (no exact date). Could this have anything to do with the new fuel pump? Should I wait to see if the SES code P0300 comes back?

Also anti-lock brake warning light is on... are there sensors or is this always a control module issue? ABS is inoporative, but hydraulics work great.

Any help on either issue is appreciated. Thanks!

 

Update: I also noticed that each time the light comes on; during a cold start there is always a ticking (sounds heavier than a lifter) quite pronounced, but goes away after a few minutes. And coincidentally seemingly happens with a full tank of gas. Light is back on. lifter sound is back. any correlation?



And I found the ABS speed sensors. Thx.

 

You could be experiencing detonation that you are likening to a lifter tap... If premium fuel helped, then you likely have predetonation which is causing the P0300 code.

Check out the DTC listings in the Tech Article (DIY) section as well as run a search for P0300 and you will find a rather large, lengthy thread on this code.

As far as your ABS light, it is most often caused by one of the WSS (whee speed sensors) either having a low mV output (needs to be between 200 and 350 mV-AC when you spin the tire) or a WSS wire being broken near the wheel.

 

Light is off again and blazer is running like there are no problems. half tank of gas again (regular unleaded) no more ticking sounds from the engine during cold start. But I am sure problems will be back when I fill'er up. All was ok until I had the fuel pump changed.

I will check the codes section for possible fixes. Thx

 

Found broken wire on ABS electrical line. patched it, ABS light has been extinguished.

 

Good deal!

 

Have you checked fuel pressure and leakdown? Ignition in RUN position, engine cold and off, fuel pump running, pressure must be 60psi to 66psi. Pressure must remain above 55psi for 3 to 5 minutes after the pump shuts off.