2000 Blazer P0300 Random misfire code
 

So I have a 2000 Blazer as stated in the title with some issues. Everything started about 3 weeks ago. I drove it to Wal-Mart, got a few things and left. It started up fine. Got to work with no CEL, no issues at all. Then after work, it would crank but not start. Then I started diagnosis:

1. Changed the ignition coil and control module and the distributor cap.
2. Checked fuel pressure, a perfect 60 psi.
3. Ran the fuel pressure tester's by-pass hose straight into the intake to dump in fuel. Viola! It started but would die quickly.
4. Changed the fuel pressure regulator and NOT the spider. I didn't do this because of cost and because when it did start, all cylinders ran like a top.

Now a new problem. Once everything was put back together, the engine was very hard to start, but it did fire on its own. But it was very rough, didn't rev up well and vibrated like crazy. I revved it up to 3k for awhile and it did smooth out somewhat. CEL came on and there was a single P0300 code. It seems to me it's not firing on all cylinders. If revved over 1700, the CEL will flash.

So with everything that's been done to it, I'm almost certain I caused it when I replaced the regulator. I haven't had a chance to check for spark on all cylinders yet. What would be helpful is a list of things to check. I'm going to start by replacing all the spark plugs and checking to see if they fouled out. I'm also considering a new distributor altogether. As for the fuel delivery in the intake, what should I check for? I double checked firing order for the injectors and the plug cables. They all looked good.

Any help is greatly appreciated.

personally, if it was me i would replace the dis. cap and rotor. also look at the fuel pressure when it is running.

my cap and rotor was a big part in my p0300 code. i still have the code because i got a leaky spider, but it needed a cap and rotor badly. the only difference between my p0300 and yours is mine is at 1700RPM and below. above it runs perfect. not a miss, below 1700RPM it runs like crap it even backfires some. what is the millage on the truck??

but anyway's, i would start by replacing the cap and rotor (like 50$) before replacing the whole dis manly because its a pain & time consuming to do. I would look at the plugs, if there really dirty you can clean them off(like i did) or you can replace them, i did not replace them because i don't have the money to do so. (17 in high school with no job ): )

The mileage is 150k. The distributor cap, rotor, and gear were all changed about 4 years ago at about 125k miles. Along with plugs and wires. But I'm about to change all the plugs right now anyway. They're cheap, only spent $20 for all 6.

Thanks for the info, 4.3 vortec. :-)

I just finished with the plugs. I replaced each plug one at a time. Before it was replaced, I pulled the cable, put in a new plug then cranked the engine to verify spark. Then, I would remove the plug one at a time. Only three plugs had fuel on them, 3 did not and all cylinders had good spark. Cylinders 6, 4 and 5 are not getting fuel. I'm going to open up the intake again tomorrow to try to find the problem with the fuel system. My first thought is to try to clean the injector nozzles. Anything else I can do?

Solved.

Once I got the intake taken apart, I removed all the poppet nozzles, set the fuel meter body back into place, reconnected the fuel lines and the fuel meter connector. Then made my gf come out and turn the key for me. When the key is turned to the on position, our CSEFI system will give the cylinders a squirt of fuel. I saw 3 nozzles not working.

Since I already knew my injectors were good, and since I was in a hurry the last time I took all this apart, I already knew the problem. Some sort and gunk got into the poppet nozzles causing them to stick closed.

The plastic clips/housing came off the nozzles by gently prying the two clips away from the nozzle near the tip. Then I doused them with starter fluid, tapped them on the intake a few times and had the gf turn the key. I had to repeat a few times, but they all eventually broke free. Then, to be sure, we kept firing them 10 more times. (Because if timers in the computer, the steps for turning the key are, on position, wait 1 sec, off position, wait 8 seconds. Repeat.)

After that it was just careful reassembly. Anyone who attempts this, be sure you torque all the intake bolts to spec. 88 inch lbs or 7.3 ft lbs. There is a ton of connectors and steps, but I am nothing more than just handy with tools and got it done. Take your time, make mental notes, double check firing orders for the plugs and injectors and give it a try.

Hopefully I was detailed enough to help someone in the future.