I'd been chasing a P0300 misfire code for almost 2 years.
I finally got it fixed and she's running like a champ again.

It was the plug wires. Like a dope I thought after 3 sets of Autolites from Advance, it couldn't possibly be the plug wires. The plug wires were brand new and looked good. I couldn't really see any arcing. How could 3 separate sets of wires be bad out of the box? Well, they were. I was close to dumping the car when my mechanic neighbor suggested a set of Taylors or anything that wasn't Autolite.

I got a set of Taylor Spiro Pros from Summit, re-checked/gapped all the plugs, ran them all tight through the stock looms for the fifth time, a set of wire separators, and convoluted tubing. I fired her up and I couldn't believe the miss was finally gone.

In my quest to fix it, I started by throwing parts at it and then wised up somewhat and started diagnosing first.

I broke a lot of expensive stuff along the way too:

-Replaced the opti twice (NEVER got an opti code even with the opti full of oil)
-Fragged a bunch of ground wires
-Cooked the starter (just dumb)
-Broke the weatherpack connectors to the coil and icm
-Fragged the ignition lock cylinder wires (think they broke from age)
-Cooked the Fuel pump about the same time I cooked the starter (fuel pressure was in 40psi range then dropped to 0 when you hit the gas)

I'm posting this in the hopes that maybe I can save somebody else a lot of heartache by pointing out some of the dumb stuff I did, and how I finally fixed the problem.

 

glad you got it fixed.

did you ever scan the cars codes after it had been running a while like before you shut it off? Im just currious. cause if i shut mine off and hood up the scanner i get a P0300 (random cylinder missfire detected) but it i start it and plug in my scanner or im driving or anytime after the car has idled for more than 30 seconds i get a cylinder #2 missfire. (i have a blown head gasket but found it interesting that the missfire code changes as soon as i shut the car off and start it back up)

I ask cause if you had checked it when running maybe it woulda pointed you to the bad wire / plug sooner.

again hope it can help someone else later down the road.

 

Yeah I scanned it about a bazillion times, and it would occasionally be a cylinder 3 or 6 misfire.

I figured that I had put 3 different brand new sets of wires on, there was no way it could be the wires, it had to be something else, so I was off on a wild goose chase basically.

 

I feel your pain.

When I bought mine I was chasing down why it was misfiring and wouldn't stay running. Swapped plugs and wires and it fired right up and ran smooth for 10 min and then just died. Traced everything and couldnt find anything wrong... just wouldnt start. The wife came out and asked it if had gas..... "OF COURSE, IT SAYS IT HAS A 1/4 TANK!" Well, that was before I knew the gas gauge blows **** and after I got mad about listening to her dig me about the gas I put 5 gallons in and she fired up..... That was over a year ago and I still hear about it when I am tinkering with the car.

I always had a miss after 4000 rpm, like the car was getting fuel cut. A few weeks back I was testing fuel pressure and checking the injectors to see if they were leaking and found out that the lower O Rings were cracked and weathered out causing unmetered air to enter. Some were so bad they fell off when I pulled out the rail. Replaced them and I havent had a studder yet so I may have fixed it....cross my fingers

 

Glad to hear you tracked down the gremlins and got it running well.

I am surprised to hear that a major parts manufacturer (Autolite) has such poor quality control that they boogered up three out of three sets of new wires that you purchased! Man that sucks. But wait, aren't the crummy Fram oil filters made by the same parent company Allied Signal?! Yep. Well, that explains it.

Don't beat yourself up for doing all that other work trying to fix that faulty wire problem. Most of us have been down that road more times than we care to admit.

 

When i did my engine swapp i couldnt get the fuel pump to prime. THe wife comes after i have been going over the wires for quite a while. She lookd under the back of the car and asks if i needed the 2 wires that were hanging down to be pluged into to something (the ABS and fuel pump conector) DUH! Thats right i did take those off when i swapped the rear last weekend. Lucky for me i think she has forgoten about it.

 

I just went through the same thing with my LT1. Only I didnt spend any money because I did'nt have any. But, my plugs ended up being defective. Brand new TR6's. I pulled them out the other day and put my old TR55s in and the problem went away. I went through hell and back changing off parts before I decided to just try putting my old plugs back in.

 

It blows my mind that I bought 3 separate sets of wires and they all were garbage. I never thought that could be possible.

But then I'm looking at my Taurus that eats a set of rotors every 6 months. What happened to quality control?

Seriously, when I was a kid helping my dad do brakes on cars, you would do brakes once or twice in the entire lifetime of the car. The rest of the car would fall apart before you did brakes again.

The metal is junk these days.

Anyway, it is awesome to be able to just drive my baby again.
This website and a lot of its resident LT1 gurus helped clue me in when I thought I was at the end of my rope.

 

[quote]That guy telling bull ****.. if you have a wire plug or coil pack broken it will trow a specific code for that cylinder broken coil pack or wire... got code p300 it say 02 closing loop something about fuel trim .. its a randoms misfires and if 1 cylinder only was misfiring it would tell me p0301 cylinder 1 or p0302 cylinder 2 etc...

Not sure where to start on that p0300 troubleshoot but that forum is clearly bull ****.. shouldnt start my troubleshoot in here...



change your dizzy with your dizzy wire on top .. if coil is external change your coil too .. should be done on all old car when you change spark plugs...


If it say p0300 closed loop fault...

What repairs can fix the P0300 code?

The most common repairs to address the P0030 code are as follows:

• Have a certified technician from yourmechanic.com verify the code with a scanner. Reset the fault codes and perform a road test.
  
• If the P0030 code returns, then follow the test procedure. It can have several problems, but wiring being damaged by excessive heat from the exhaust is most common. Make certain the wiring is in good condition and has proper voltage and ground to the sensor before replacing the sensor.
  
• With key on and the engine off use a voltmeter to check for 12+ volts fused battery feed to the heater element. If there is no voltage present, repair open or short in the 12 volt feed circuit but first determine if it is necessary to replace any fuse blown from the short.
  
• If the battery feed is correct, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit. If there is infinite resistance, repair the open in the circuit.
  
• If the control circuit is good, suspect a bad O2 sensor. Replace and re-check.
  

The P0030 code is a relatively common situation as it is located in front of the catalytic converter and gets considerable heat generated from the converter.

 

You appear to be unfamiliar with the LT1 (Gen 2 SBC) discussed in this thread. If you were, you would know that he DID replace the “Opti” (Optispark distributor with integral optical cam position sensor), TWICE.

You might also want to consider that he actually had a true RANDOM misfire (P0300), due to poor quality ignition wires, allowing cross-firing, and multiple cylinder misfires.. Hence he did not get a code for a specific cylinder misfire.

P0300 (which you appear to randomly type as P0030) is for “Engine Misfire Detected”, per the factory service manual. It is not for “closed loop fault”.

The rest of your post appears to be a copy and paste of the steps for tracking down a heated O2 sensor fault (P0030), which is not applicable to this engine, again per the factory service manual. Apparently you looked up the wrong code on “yourmechanic. com”.

Not sure why you decided to call the quoted post (or are you calling the entire site) “bull****”, when you apparently do not have a clue what you are talking about.

We're happy you decided you “shouldn’t start my troubleshoot in here...”.

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