Hi Guys,

I am having some major issues regarding my 1998 blazer 4.3L 4x4.

Here are the engine codes I have gotten recently.

PO300 - Engine misfire random or multiple
PO304 - Misfire cylinder 4
PO305 - Misfire Cylinder 5
PO101 - MAF or VAF sensor performance problem
PO442 - EVAP leak detected (small)
PO446 - Evap emission control system vent control circuit
PO453 - Evap emission control system high input

While I drive on the highway after 5 minutes or so at about 110km/hr in 4th gear (i assume) at 2100RPM I can feel my truck studder and it is hard to maintain that speed and my engine light is flashing. It only happens when I am on the highway.

The other codes have come and gone all while doing normal city driving or in conjunction with the highway speeds. Usually I will get a mix of them.

Recently I have changed my cat, replaced my plugs, wires, cap and rotor and the O2 sensor just after the cat as well as a new gas cap. I took out the MAF sensor and cleaned it out as well as looked at the EGR valve and it looks good.
I have also recently changed my fuel pump but replaced it what seems to be correct (had to change the wiring harness due to the new and improved ones that NAPA sells.

Ya its been a good year for my truck.

Any ideas guys what could be causing this. Is it all caused by one simple problem (i really hope so cause my gas milage is horrible).

Thanks a mil

Mike

 

Have you done your research on the codes in this section:
Diagnostic Trouble Codes (DTCs)

 

multiple codes uasually means the vcm (computer) is bad. Had the same problem and spent a fortune replacing ALL the sensors only to find out the computer was bad, even though it was reading as funtional. Have seen this problem on other GM vehicles, and it was the computer on those too. You can get a computer at the junkyard uasually for $25 to $50. just make sure it is the exact same year make and model, and the same engine. Good luck !

 

Maybe it was the cause in your case and a few select others, but to jump straight to that conclusion without proper testing is reckless.

Seeing as how many of the above codes are inter-related, it could very easily be a few simple problems completely unrelated to the PCM.

P0101 - Mass Air Flow System Performance - This code can cause the misfires.
P030x - Random/Multiple Cylinder Misfire Detected

When was the last time a full tune up was done on the truck? Have you tried cleaning the MAF sensor?


The EVAP codes could be caused by a malfunctioning vent solenoid (under the back of the truck).
P0442 - Evaporative Emission Control System Leak Detected (small leak)
P0446 - Evaporative Emission Control System Vent Control Circuit
P0453 - Evaporative Emission Control System Pressure Sensor High Input

 

Recently I put a new cap/rotor, plugs and wires 1st as well as cleaned the MAF. I thought that would clean it up and I'd be good to go... Guess not. I have all the testing procedures listed in the engine code section. hopefully I can get all this tested before the sub-zero temps set in... my vehicles always go down in the winter.

Thanks for all the help guys, i'll keep ya's posted when if I get this solved.

Mike