Misfiring Woes

1998 Blazer 131000 miles, 4.3 l, 6 cyl, 4X4

Two days ago at a speed of 60 mph my Blazer's motor began to misfire and the "Check Engine Soon" Light came on and then began to blink on and off. I pulled over and took my scan-tool (a reader...Accutron, $80 model) and a
P0300 error wich told me that a random series of misfires was logged. I cleared the code, drove on (40 miles from home) and the light came back on immediately and the engine was misfiring.

Reading the code again I now had a SPECIFIC cylider misfire (P0305) which told me the # 5 cylinder was at fault. After several code readings the last two days, the error code has ALWAYS been P0305. The P0300 never logged again.

I am haven a dickens of a time with this problem and I cannot seem to solve it. So far I have changed the #5 wire and spark plug with new parts and I still get the misfire.

I used an ignition spark tester by connecting it to the # 5 plug wire and starting the engine. It appeared the spark was normal and strong although it may be my aging eyes, but the blue spark sometimes had an "arc" shape instead of going straight across from node to node. Again, I'm not sure if this is an issue.

I checked the ignition coil primary with my handy Sears digital multimeter and read 1.5 ohms that quickly decreased to settle to .6 ohms across the primary as if I had some type of capacitive element involved. (Haynes service manual says .5 ohms is maximum but again I am not sure about the accuracy). The secondary resistance meaured 6 k ohms (Haynes service manual says 5 k ohms to 25000 k ohms is acceptable).

The distibutor cap and rotor were changed out (by me) 5 months ago but I removed the cap and rotor this morning and found no hot arcing spots. I did find that the six nodes to be coated with a white, chalky substance which I cleaned up with a pencil eraser. I re-assembled the rotor and cap, wired it up but it still misfires with the PCM returning a # 5 cylinder misfire.

So, I am at a loss and the ol' back is broke trying to reach plugs that are (impossible??) most difficult to get to. So far I have replaced the number 1 plug and the # 5 plug, and their corresponding plug wires and also the # 3 PLUG WIRE. I cannot remove the # 3 plug as there is a steering shaft in the way it seems. I have not even attempted to get to the 2, 4, and 6 cylinders (plugs and wires) as they appear to be even more inaccessable than the three on the left side of the motor.

Could the scanner be sending me a lousy error code by perhaps having another cylinder misfiring and the PCM is (for unknown reasons) defaulting to the # 5 cylinder error code (P0305) ?

Is there something else I am missing here and should be checking ?

The Haynes manual leaves alot to be desired some times. It appears as though I have a High Energy type coil and a CSEI (???) disributor system.

Missed two days of work already and any help would be very much appreciated.

Thanks,

Paul in Massachusetts

I've had this very same problem with my 2000 blazer it keep throwing multi cylinder misfire codes. I found out after replaces plugs and wires I still had the problem. Believe it or not I stumbled on a fix by taking it out on the highway and beating the shit on the engine continuously going from the speed limit to passing gear and ending up cleaning the injectors out this way. I have never seen that code or any other code yet and that was 2 years ago. Ever since I've been running Lucas fuel injector treatment on every other tank and I believe it's helping. Don