Hello, I am new to these forums, so please keep that in mind. I have searched through these threads for something similar to my condition, but I have come up with no luck, so I started a new thread. If by any chance I happened to have missed it, please direct me to that thread so I can take a look because this has me at my wit's end. If I have posted this in the wrong forum topic, I am sorry for that as well. I will give a quick run down for those that don't feel like reading a small story and then go into detail to completely explain my problem and steps I have taken to try to correct it.
Long story short, I am misfiring in cylinders 3, 6, and on occasion 1. I have changed out my cap and rotor, plugs and plug wires. I have also done the MFI conversion for the fuel injectors to get rid of the poppet nozzles. My compression is good all around (150PSI+). I have cleaned my MAF and I still cannot get my check engine light to stop flashing at highway speeds. I get P0300. Hope this gives someone any possible fixes for me. And now the details.
Okay, so I about a week ago I got a 2002 Chevrolet Blazer Extreme 2WD. It has almost 83,000 miles on the 4.3L Vortec V6. Everything seemed fine until I drove it on the freeway for the first time. Once I hit about 70MPH, my check engine light started flashing. I know that means that my catalytic converter is going to clog up and get ruined if I keep driving it while it was flashing. So I slowed down and was about to get off. Once I got down to 65, the flashing went away and the check engine light did not stay lit. I sped back up and the same problem happened. I basically knew that I was misfiring.
I assumed that a tune up has never been done, so I figured I would do it. When I got home, I changed out the spark plugs and wires. Changed the oil as well. I go back on the freeway and I get on it while I'm going on the on-ramp. As soon as I hit 70 and above, the Malfunction Indicator Light begins to flash again. I slow down and this time it stays on. I go to my shop because we have a scanner there. The code was P0300- Cylinder misfire detected. I go into the datastream on the scanner and it shows that cylinders 3 and 6 are misfiring. It does it at idle as well, but not enough to set the check engine light off or cause it to flash. I drive it home in town and the light goes away.
The distributor is what popped into my head. So I changed out my cap and rotor. Problem still not fixed. Same thing happens. From there, I started thinking fuel problem. I read that the poppet nozzles on this are notorious for going bad and saw that many people to the MFI fuel injector conversion. I spend the $300 and sprang for the conversion. After I get them in, I check it with the scanner and it is still misfiring and now cylinder number 1 does it every once in a while when I rev it. It might have been there before but I might have not noticed it.
Having put in a new fuel deliver system, new cap and rotor, new plugs and plug wires, I now think that maybe there is something wrong with the internal components of the engine. And easy way is to check my compression, so I did that. It was 150+ PSI all around. So my valves are good so it can't be something as serious as that, which is a sigh of relief.
I read that the MAF sensor can sometimes cause this problem, so I get some MAF cleaner and clean it out, but I had no luck with that. I am seriously at my wit's end with this truck. I have tried everything that I know and that comes to mind. I need your guy's help.
I used to be able to set the check engine light off and cause it to flash when I would rev it in park or neutral, but after I replaced all these parts, it only does it when I am driving at high speeds. So I guess I fixed the problem a little bit at least. The engine does not seem to be greatly affected. It does not bog down, it starts right up, I can cruise just fine in town. Once I get on the freeway, it goes downhill once I hit 70MPH. It seems to begin to vibrate a bit and then the light comes on. My gas mileage isn't doing that great, I don't know if that because of the constant misfires even while I drive it in town or if the Blazer does not get that good of mileage to begin with.
So yeah, that's basically about it. Well at least all I can remember off the top of my head. Did I miss something in my diagnosis that could lead to me fixing my truck? It's a nice truck and I would love to keep it, but I don't want to keep pouring money into it if I cannot rectify my problem. Please, any insights are more than welcome. I have run out of ideas. If you have read this far, I am very greatful. Thanks to all of you who have taken a few minutes of your time to read through my thread. I hope to get some responses soon so I can finally not have to worry about my new vehicle.