Is PO300 active when the engine is in open loop mode? I had a nasty PO300 that caused all kinds of misfires EXCEPT when the engine was in open loop mode. Then as the engine warmed and transitioned into closed loop mode the code suddenly became active. The problem turned out to be a corroded O2 sensor connector on the left bank. Cleaned the harness connector, replaced the O2 sensor, and applied dielectric grease to the terminals and the code when away. Truck has never ran better!

98 Blazer 4wd

 

Hi. Got two new ac delco O2 sensors..... and same thing.... flashing cel. Cylinder one and four now misfiring equally / at same rate. So then I installed a new distributor......NO more misfire....YAY................BUT now getting a po341 code. So im guessing I need a case relearn....but before; do I need replace the Crank Sensor under the front of the engine? Thanks? More infor on code po341 will be helpful. Thanks again.

 

just a guess, but did you try disconnecting the battery for a while?

 

hi blazinloud..... the negative cable was unhooked before and after installing distributor. Clear codes with scanner....been at work since after, will go out there and check it out today. Sure happy i can now install my cat.

 

Ok problem solved. I install two faulty cam sensors, replaced this time with genuine acdelco and put in a new cranksenor then took it from a case relearn at a gm dealer... They did it for free! (I went in expecting to pay 120 for the relearn and so should you.) First aftermarket sensor made cel flash at 2500 rpm with huge missfies on 1 & 4 equally.... Second aftermarket cam sensor no misfire, but code po341.

 

Glad you got the problem solved! I try to always steer people towards AC Delco sensors and ignition components. Their quality control seems to be quite a bit better than other aftermarket suppliers. It is unfortunate that you had to find out the way you did though.

 

With a P0300 and P0301 and P0304 check your spider for leaks. Pull the top half of the intake, then reconnect your fuel lines to the spider, plug it in and turn the key to ON and look for fuel leaks from the lines or the regulator. If the regulator leaks it dumps fuel directly into the runners and fouls plugs. I just did mine today. Replaced the regulator which was leaking and now runs great again.