View Full Version : Need Tech help

02-19-06, 09:16 PM
I have a Maggie with SW headers and RT CATs. Since the Maggie install earlier this week I am constantly getting the CEL "P0300" (random misfire). I clear it and it goes away for awhile, then comes back. I cleared it last night, drove a little bit, got up this morning and drove to work, all OK. I start the car to go home and let it idle for a couple of minutes to warm up and the damn thing comes on again. The car appears to run fine. It comes on under all different conditions, I have cleared it 8 times this week. I have run the car with the superchips tune and the stealthV tune and still get the CEL. I am afraid perhaps this might be damaging something or maybe it's nothing but an annoyance.
I have the following thoughts, since this is a random misfire it would appear that it would not be a sparkplug, sparkplug wire, wire connection to the coil or the coil itself as that would be on a particular cylinder and would generate the appropriate CEL for that cylinder. I have new plugs and wires and have checked connections. Plugs are Iridium NGK 55's gapped at .40 (same as stock).
The summary for the cel says:
"The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set. Conditions for Setting the DTC The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards."

Could it be the Crankshaft position sensor needs to be recalibrated. (I read something, somewhere in the FAQ's about when that needed to be done but don't remember).

Any ideas or help would be greatly appreciated....

02-19-06, 09:53 PM
It seems most likely that a plug wire isn't fully seated on a plug, or is damaged (plug or wire). I'm no expert on the CKP issue - but have not ever had a P0300 code EXCEPT when I didn't get the #8 plug wire all the way back on (easier to do from underneath the car, believe it or not).


02-20-06, 12:05 AM
I have SW headers on my Z06 and have the same problem as wildwhl with rear plug wire. I have put it on 4 times knowing it is on tight an snaped on the plug yet I will still get a random misfire code, check the wire and its loose. Finally it has stayed on but it made me question my ability to install a plug wire several times:thepan:

02-20-06, 11:43 AM
anyone else? I will install new plugs next week (going one range colder) and re-check wires.