P0300... what causes this?

[gc96z28]

What can cause the P0300 code, random/multiple cylinder misfire detected? I have new plugs, wires, cap, and rotor.

[LS1 TA]

I have a 3rd gen with a regular distributor, and I'm not real familiar with the opti spark. What I'm trying to say is this is just a shot in the dark guess. Maybe one of the wires is on the wrong plug, or on the wrong post on the distributor.

[Injuneer]

Is the SES light flashing, indicating an "active" code? With long tubes, it isn't unusual to have problems with burned wires, arcing, etc. Have you inspected the wires closely? Even if they are new, doesn't take long to burn them. Possibly a loose or damaged plug from the recent replacement?

Did you do all that work in response to eh P0300 code, or is this a recent conditon, after doing all those replacements?

How many miles on the car? Any particular reason you didn't replace the complete Opti? Have you ever pulled codes for problems with high or low resolution pulse patterns from the Opti?

[gc96z28]

the light flashes sometimes, but it's usually solid. the guy that did my cap and rotor said the distributor itself was fine. Wires are good, no burn or nothing. Fresh oxygen sensors on as well. I have no idea.

All this was done in repsonse to the code.

there are 65,000 miles on the car.

[dochidalgo]

......then check each spark plug & connections carefully or replace them...Check each fuel injector, some must be damaged or dirty....(my car had this DTC and the culprit was an injector), the GM dealer scan tool can tell you wich cylinder is firing the DTC...is the easy and expensive way but the most secure to get a correct diagnosis of your problem
Good luck man
Dochidalgo

[Eric 97LT4SS]

Ever since Modding my engine and having a Custom Superchips program installed that very same Code keeps popping up about fours times a year or every 2K miles. I was told by the "Shop" that the HOT Cam was causing the P0300 Code to pop the SES light and that the only fix would be an LT1 Edit program. This of course would cost an additional $400 so I just keep erasing the Code because the Motor doesn't exhibit any problems that a Mis-firing cylinder would cause, revs perfectly to 6,500 even when the SES light is lit. Although my car & motor only had 14k miles, we decided to re-use the Original Opti along with the Cap & Rotor. During the surgery I had G2 Superwires, NGK plugs, and #24 SVO Injectors installed and they are all still perfect as far as I can tell. But, I have never actually pulled a Plug to check their condition. I do plan on installing MSD's new Cap & Rotor this Spring to go with their Coil and Digital-6 Plus Igintion which I am currently running. So, is the Shop right or do I have something else going on Internally?? Later

[dochidalgo]

With a new cam other than stock the reprogramm as you already know.
First you have to know in which cylinder the misfiring is happening. If is the #1, check the EGR valve hanging open or is dirty. Running out of fuel (INJECTORS) can set this DTC, excessive vibration from tires, brakes, driveshaft. Again, spark plugas and cables. An erratic camshaft sensor and the opticrap of course.

good luck
Dochidalgo

[Eric 97LT4SS]

My motor doesn't have an EGR valve but, you bring up a good point regarding determining which cylinder is "supposidly" misfiring. Can only a GM dealer Scan Tool determine this, because Autozone can only erase the Code. I have an Actron Super AutoScanner CP9145 which I haven't cracked open yet, wonder if it could tell me which cylinder is acting up.

gc96z28 Is your motor still pulling good or is it stumbling as the RPM's climb?

[dochidalgo]

As far as i know and see, the GM dealer scan tool can give an each cylinder graphic in real time....a very accurate way to get the misfiring cylinder, and the injector pulse as well.
Regards Eric
Dochidalgo

[Injuneer]

AutoTap (with the "enhanced" option) can give you the misfire history by cylinder. I don't know about the Actron 9145. I just picked one up, and so far I haven't been able to read the "enhanced" data from my 2001 Silverado. It just seems to read the very basic data.... not quite what I thought it would be. But I haven't spent a lot of time playing with it, so maybe there's a way to get beyond "basic" OBD-II data readout. Obvioulsy the dealer's Tech-2 will read the misfire history.