WHY are you using an injection cleaner..and why didnt you mention that in your 1st post?
With your scanner, recheck the P0300 code, then look for a setting that reads "Freeze Frame Data". then access that data.
You will see engine operating conditions at the moment the diagnostic trouble code was recorded. You will see RPM, MPH, LFT and SFT(Short and Long Fuel Trims) and ECT(Engine Coolant Thermosensor).
These readings will allow you to recreate condition to again set the trouble code.
Look closely at SFT--this reading will tell you of the engine is running lean(a positive % or rich(a negative %). Ideally you want it close to zero, but plus or minus 5% is fine.Then look at LFT--if SFT is low or zero, but LFT is high, the engine control unit has shifted the operating parameters to compensate for a lean or rich operating condition.
Record the code and Freeze Frame Data, then use the scanner to clear the code--which will reset all engine operating parameters back to factory spec. This action will also clear the Freeze Frame Data. Be sure to disconnect the battery afterwards, and step on the brake pedal for at least 30 seconds to clear the Keep Alive Memory. From that point on, any code or data recorded will be new.
Freeze Frame Data is valuable in determining what system your problem is located in.
Remember--the code doesnt tell which part is bad, it merely guides you to the system the failure has occurred. The days of "Get a code, get a part" are long gone.
---------- Post added at 08:11 PM ---------- Previous post was at 06:55 PM ----------
i bought an OBD II scanner and it said no current problems. it had one code in the history P0300 random misfire. but it ran normal when i tested it and it sounded like normal. im going to just wait and drive it til it happens again, and keep the scanner with me. maybe it was just a bit of bad gas or gunk got in there. because since ive had the truck (2 weeks) ive been running Lucas injector cleaner and UCL, and maybe its just clearing out a bit of crud? any other ideas/suggestions?
EDIT: drove it for a bit, and it happened P0305 cylinder 5 misfire... so i happened to be near a Kragen auto parts, and they suggested it was the coil for cylinder 5. is it difficult to replace?
Very easily could be #5 coil, and not difficult to replace. At least now you have a direction to take, as the code indicates a problem with #5 cylinder. This rules out a MAF, IAC, and other items which would affect all the cylinders, not just #5. Keep in mind--a missfire can be caused by a compression problem, injector problem, vacuum leak, and any ignition component affecting #5 cylinder. Missfire does not automatically mean it's an ignition fault.Your earlier P0300 suggests that at one point you had more than one cylinder missfire at the same time.
I suggested reading your Freeze Frame Data to see if your fuel trims were correct. If so, then the problem certainly could be an ignition issue. Rule of thumb--if you replace the coil, replace that cylinder's spark plug at the same time, and if the plug wire to that coil is high resistamce(open as measured with an ohmeter) or shorting to ground(use an alligator clipped wire, grounded at one end, the other run along the wire) replace that coil's wire as well.
