I'm back...changing out the CAT didn't help. I got a new CAT in from Summit, changed it last week then went on a road trip this weekend. The Blazer still lacks power, it used a full tank to drive 2 hours down the freeway at 70mph, I couldn't even keep up with traffic on the inclines. My tail pipe tip now has a 1/4" carbon ring around the end of it.

It popped a code during my 2 hour trip: P0300 - Random Cyl misfire. On the freeway, the SES would flash while it strained on an incline.

This morning I pulled all the plugs and found cyl's 2,4,6 normal; cyl's 1,3,5 were completely covered in carbon. After I saw that, I did a compression check on all cyl's and luckily they were all 178-182. Checked fuel pressure for the heck of it, it was 61 psi (KOEO) and dropped 4 psi in five minutes or so after the pump primed.

Chasing this misfire down, I've already replaced the EGR Valve, both O2 sensors, distributor, cap, rotor, plugs wires and most recently the CAT. I gave it some fresh plugs today, but I know the problem is coming right back. Now I'm thinking something to do with the intake manifold??? Since it's fouling only the left side.

If I don't get this figured out soon, it's going to the shop. My Haynes manual is of no further use. If any of you have any other ideas to help me figure this out, I'd surely appreciate it...Thanks!

 

Ok, guess I'm taking it to the shop. We'll let the pro's figure it out. I'll post what the fix was when I get it back.

 

Have you checked out this thread?
https://blazerforum.com/forum/diagnostic-trouble-codes-dtcs-49/p030x-explained-x%3D0-1-2-3-4-5-6-a-35153/

 

It seems to me that you have a problem with one particular side of the engine. Seeing as how you checked the fuel pressure leak down and it sounds reasonable, that would rule out the fuel pressure regulator leaking fuel into that side of the engine and flooding the cylinders with gas. The next easiest thing I would think to look at is are you losing coolant? You may or may not see puddles beneath the car depending upon where it may be leaking, so keep an eye on the reservoir. A leak in the lower intake manifold is fairly common on these engines.

 

I just got off the phone with the mechanic. He ran his diagnostic on it and found that after the car warms up, the injector pulsewidth on cyl's 1, 3, 5 increases by 25%, opening as much as they can to compensate for a reported lean condition. The SES light came on without setting a DTC. The P0300 code seems to be spot on since the injectors are going full open and fuel-fouling the plugs. Tomorrow he's going to try swapping O2 sensors from left to right to see if the problem follows. He also said if the O2 sensors are not the problem, it's more than likely the PCM.

After reading posts on O2 sensors, I can see where my new sensor I just put in could be culprit. It wasn't an AC Delco sensor, but an el-cheapo from my local auto parts store. Guess we'll know more tomorrow.

I'll be relieved to discover it was something so simple, but upset to find out one of the new sensors I just replaced has already failed.

 

Im EXTREMELY interested in the results. I'm going through the exact same thing. I'm throwing codes p0143 (O2 signal, low bank 1, sensor 3), p0300 (random cylinder misfire), and p0404 (EGR feedback signal out of range). I'm misfiring on cylinders 1 and 6 though which are on opposite sides of the engine. I also did a compression test and got 175-180 psi on all cylinders. Plugs 1 and 6 are much more covered in carbon than the others. I think we're in the same boat, so any information you find out I'd much appreciate it, and I'll do the same. Hopefully it's just an O2 sensor! Cheers

The link listed above has a ton of diagnostic information but I didn't see any actual results. It seems like people have replaced EVERYTHING to try to fix this problem without getting to a solution.. Has anyone had a definitive fix to the common p0300 problem??

 

My problem is starting my ol girl... My problem is i haven't put the code reader on her lately. But when i start her foot to the floor, and cranking away she fires up smokes blue and smells like gas.... lol

 

I have the same problem except when my 1996 blazer warms up, the misfire goes away for the most part. I have read about this same problem(P0300)
over and over on this forum, and after everyone does the same ole' same ole', etc.(plugs, wires, dist. cap, fuel filter, etc.,etc., ) I have yet to find any cure, just symptoms. I must have missed it. If someone knows what this gremlin is, could you repost it or better yet, send me an e-mail, I am at my wits end trying to figure this out

Oh yea, this is Sam, my e-mail is dsnl@gmail.com
Thanks