Alright, I'm turning to the masses here at BF to help solve my problem. I've done all the reading and tried out a few things but I can't seem to cure my Blazers P0300 misfire.

I've done:

Spark plugs when I first got it. Seemed to cure the miss... for about a week.

Spark plug wires. Also seemed to cure the miss... for about a week.

Different plugs, AC Delco plugs. ""

Replaced the cap and rotor. ""

Had a friend at a dealer scan it with a Tech 2 and saw that it was missing mostly on (if memory serves me) Cylinder 4, moderately on cyl 6, and barely on cyl 2. Nothing on the other bank. He hinted, as most do on here, that it may have been the fuel spider.

Replaced/upgraded the fuel spider. Seemed to cure the miss for a few hours and it returned. Again.

Now it mostly misses when it is cold/ has been running for less than 30 min. Not to say it won't after that but it isn't as prevalent. It also seems to go away if I floor it. I'm really at my wits end with this thing and I don't want to be throwing money at it when there are other things that need addressed. So, with that said, any input fellas?

PS, anyone have the part numbers / good place to get fuel supply/return lines from tank to filter/transfer case. Sprung a leak during the fuel spider swap from, I guess, releasing/rebuilding pressure in the system.

 

Hmm. Have the fuel system pressure checked. Must be around 60 psi at key on. and hold above 55 psi for 10 min. For example If it pops up to 57 and drops below 55 etc then id suspect bad pump. Have you replaced the fuel filter?

 

2x what chris said
DO a fuel pressure diagnosis

96+ Fuel System Diagnosis - Blazer Forum - Chevy Blazer Forums

also what brand cap and rotor did you use
These engines prefer ac delco for all ignition products

 

And it is all on the right side it seems for what that is worth.

 

Update: Fuel pressure is fine.

It really seems to be spark related and I did not install an AC Delco cap/rotor, just whatever AutoZone had in stock. I went ahead and got an AC Delco cap/rotor and put them on and it seems to run a bit better... but now I've got a dead miss on cylinder 2. Completely dead, no spark. Every other cylinder is fine and the wires should be too as they are only a few months old and are AC Delco wires.

 

did you pull that plug and see if it fouled?

 

Never assume anything. Even with new and quality parts. Hope you kept one or more of the old wires.. I always do, esp if I've got a chronic problem.

Or ohm #2 out compared to working cyl.

 

Hmmm, every other plug in the firing order, check the distributor bushings and drive gear for wear. Also check camshaft retard, should be zero degrees + or - 2 degrees.

 

Its possible you have an intake gasket problem. I was running only two good cylinders on my 97 blazer, until I replaced the gasket. Now i've got one or two cylinders misfiring every once in a while.

Good luck. I know how much these trucks can be a pain to work with.

 

I swapped plug wires to verify they were good and they were. Turns out, somehow, something burnt out in the cap causing #2 to be dead. The weird part is the burns are on the #1 "track." I also went ahead and got a reman'd AC Delco distributor because the one in the truck had a lot of slop anyway. Put the new dis in and swapped with the last cap I had and she's running without throwing any miss codes.

Now I've got a bigger problem because when I took her out for a highway test ride to get a drive cycle on it I lost 3rd and 4th gear. Appears the 3-4 clutches burnt up. Awesome. This truck is really testing my patience.