Greetings to all, it has been a while since I have checked in.


My wife's 1999 Blazer just threw a P0300 code at me. It ran like crap, she parked it and took my truck. I went out a few hours later and it was running fine. She went to pick up my son from baseball practice and again, no problems. The Blazer has about 130k on it, and I think the plugs, wires, cap and rotor were all changed about 30k ago when it gave me the code that time as well.


My two questions are: if the truck is running ok now, should I just consider it a random thing?


And, how tough is it to get to the plugs, wires, cap and rotor to change them? As I understand it, I have to take the inner well off to get to them, is this true?


thanks for any info you can give me.


Dino

 

If you have large/big hands...then yes going to be a tough job for you. Two things special about the 4.3L engine:
1) plugs wires at distributor are not in sequence on driver's side, 3-1-5(I think), passenger side is 2-4-6. This is front to rear on both.
2) getting plug #3 out requires either a special wrench, going through the fender wheel liner, or unbolting the steering shaft and moving out of the way. I have always just moved the steering shaft; pop-off plastic cover, remove one bolt, then compress shaft and move out of way. Shaft can only go back one-way so no problem with steering wheel alignment.

Be sure to use only GM/Delco plugs, cap, rotor.

Good luck.

 

Thanks for the info. My wife drove the car around today and said it ran fine, so I am not sure what happened. Is a random misfire common once in a while? The plugs, rotor, cap, filter and wires all have about 30k on them, so I don't think they are too worn yet.

 

That's the way I do it. To me, it's easier than jacking around trying to find some perfect angle to get to it. Pop off the shaft, and there's suddenly plenty of room!

 

For me and plug #3 I put the spark plug soccket on the plug and then I`m able to catch enough of the 3/8s drive with an extension to pop it loose

 

Update to the situation. Wife was driving the car around yesterday and the CEL went off and the car is running fine. I think I read somewhere that if the computer gets a certain number of OK's when it checks the system it resets. Does this sound right? Thanks again to all who replied.

 

Yes, the computer will turn off the check engine light after what ever condition caused it is gone for long enough.

When ever I have a CEL come on, but the vehicle exhibits no symptoms, I'll clear the light with my scan tool. If it doesn't come back, great, there must have just been a hiccup somewhere. If it does come back, time to investigate.

Since yours was running bad for a little while, there is probably something wrong with it. If it's running ok now, I probably wouldn't start replacing parts right away. It's pretty tough to diagnosis something if the condition isn't there! I would be wary,though, and keep a sharp eye out for signs of trouble. Usually, cars don't heal themselves.

 

My thoughts exactly. Maybe it just misfired one time as a fluke, and it corrected itself, but I will keep a watch on it. I have a mechanic that I like to use, so if it acts up again he will be checking it out. My hope is it is just a one time thing, but my luck is usually not that way.


Thanks for the reply.

 

Question for you, what was the humidity like outside at the time of running poorly? Any recent rain? Was it raining then? Reason i ask is because missfires during damp conditions (like sitting overnight and the engine is cold allowing condesation to form) is an early sign if ignition component failure, i have a Blazer and 2 Astro vans that are real bad about this (Same Engine and Ignition System), i put high quality plugs wires cap and rotor in them and have never had a problem since, however the first time i used Oreilly store brand junk because i was being cheap and they never fully cured the problem and lasted about 25k miles before throwing codes again, i chased my tail for a while looking for a "new problem" because i "assumed" that everything was still good since it didnt have that many miles on it....... until... i ran it in the total darkness in the garage one night and found a light show coming from my distributor cap and plug wires, its now 60k later after putting good parts on and havent had single misfire code since.

These ignition systems are designed to jump the spark across a long gap inside the distributor cap, this in turn forces the coil to produce more energy before it releases the spark, then the spark is sent down the wire to make a nice hot spark at the plug. Incorrectly gapped spark plugs, high resitance in cheap plug wires and corrosion/moisture in the cap will make this gap jump, plus the added resitance, just too much for the coil because there is not an easy path for it to take to graound, so what happens is, the spark is released within the coil itself which will damage it in a short time, the spark being released inside the coil is why you usually feel a buck or jerking, its cutting more than one cylinder for each time it happens, the cylinder that the spark was supposed to go to misses and the next cylinder and possibly one more mis because the coil is recovering from an internal high voltage dump (it's also why you get "Random" misfire, its multiple cyliders and happens to any given cylinder), its like youre turning the key off for a split second cutting spark, it may still work just fine sometimes but everytime it drops the spark internally it hurts it even more, this is why testing procedures will tell you to ground the the coil wire if you need to crank the engine without sending spark to the distributor, that spark needs to go somewhere, preferably Ground to the block, not inside the coil.

Anyway, the point here is to use high quality name brand parts like AC Delco or Delphi and you shouldn't have any more problems. One weak link in the sytem and it throws everything off. MSD makes a coil for these engines, Part No. 8231, i'm running one now and have had good results so far, they can be had for about $35 on ebay, i guarantee they are better than the low quality crap that most shops will put on and probably even cheaper priced. If it keeps giving you trouble try watching the distrubutor cap at night in a completely dark place like a closed garage (Obviously not for very long though!) If its making a little light show back there then Replace the Coil, Distributor Cap, Rotor, Spark Plugs and Plug Wires with AC Delco or Delphi Parts or the MSD Coil i mentioned, chances are you wont be messing with it again for a long time.

Sorry that was probably way more information than you needed but it's good info about the Vortec Ignition System.

Hope this helps!

 

Wow,, thanks for all the info. Not too much at all. I am not sure what parts were used as the mechanic did it all. It had about 100k the first time I changed everything, so I knew it was due. This time we are at about 30k, so not sure if it is due or not.

I live in the SF bay area, so humidity and all is never a problem. The car had sit for a few days as my wife is a teacher and on spring break, but nothing that I would say was out of the ordinary.

I did the garage test on an old 79 Camaro I had when I was in high school, and it lit up like a tree. Ended up replacing the coil I think. Either way, for now, it is running well, so I am going to leave it be.

Thanks for the info, and taking the time to type it all. I appreciate it.