Ok, I've been searching around a bit on the P0300 multiple misfire code, and it seems that the multiple misfires has multiple possible problems, so maybe with my details, someone can help me narrow down where to start...

97 Blazer LS, 2WD, stock, 130k miles. Little overdue for an oil change, also has that annoying P0446 Evaporative Emissions Vent code... (I'll worry more about that with warmer weather)

Stumble/hesitation/misfires started about a month or so ago when we had a little warmup... So I started paying attention... If the temp is below freezing, almost no problems, if the outside temp starts climbing and gets above 40, I start noticing it a lot more... Happens in town, interstate, accelerating, whenever, sometimes at idle, but not as much...

Should I start at the plugs and work my way through the wires to the cap and rotor, then start checking for vacuum leaks and such if nothing seems to be wrong electrically? Should I start at the cap and rotor and work to the plugs? Should I start with vacuum and air intake?
Does it matter where I start? All of the above is a hassle, as I'm sure you all know the way things are wedged and routed and shoehorned in... and I've got big hands which means I usually leave a little blood on the motor somewhere...

It just makes it mine.

Thanks!

 

check the plugs first, cheap to more expensive route and when replacing parts use only ac delco. These trucks are fussy

 

dont forget NGK.

 

I fixed one of those codes (P0300) on my 2000 Blazer 4X4 LT with new Rotor, Dist. Cap, Plug Wires and Plugs and fixed the other (P0446) with a new Gas Cap. I used ALL new AC Delco parts.

Good luck...

 

Well I took my aftermarket locking gas cap off months ago, put the original back on... 446 code has been cleared and came back multiple times...

Plugs are either NGK or Delco Rapidfire (I'd have to check my log at home to confirm which), wires are MSD if I remember right, cap and rotor are Delco also I believe... Only thing not "stock" is a Cold Air Intake, and I've already checked it for leaks, because I had that problem once before, and filter is freshly washed and oiled.

I haven't cleaned the MAF sensor since last summer... last winter got a new fuel pump put on... And I believe two O2 sensors replaced last spring... I'm at work at the moment, so can't get specifics on everything right now, it's home on a spreadsheet...

Going to check things out Saturday and see what I can find...

 

Well, checked it Saturday, couldn't find anything obvious... didn't have as much time as I expected, but checked plugs, wires, cap and rotor, air intake, and everything was good, tight, non-cracked etc...

Drove it Sunday, no problem.

Went to take my son to school yesterday morning... Cranking like mad, no fire, no catch, no cough, just cranking and cranking...

Now I've got to figure out if I'm not getting fuel or not getting spark... I've got a funny feeling it's no spark somewhere...
Is there an easy way to check for spark on your own (alone)? I've got a spark checker, but it normally needs someone under the hood watching it while someone else cranks... And my under-hood remote start switch is a huge hassle to hook up (especially in a muddy dirt driveway...), is there an easier way? If I can't figure out a way to test it by myself, I'll have to wait until the weekend to get some help with it, as my work schedule doesn't mesh with most others, lol.

 

i have a 2001 chevy blazer ls 4wd with 108k. about a week ago i fixed a hissing vacuum line and drove it the next day to work had no problem. when i got off work it ran like crap till i was able to get on it a little bit and it missed pretty bad and then came right out of it and ran fine the rest of the way home. finally the check engine light came on. the codes came up as a p0300 and p0452 so i checked the cap and rotor looked good and wires look. changed the dia-electric grease on the icm pulled plugs and looked ok. nothing worked. so i took it to the shop and they had it for all day spraying vacuum lines and intake. found nothing found that i was missing on cylinder 2,4,6 and noticed the fuel trims were on the high side which they said would be lean condition. did a fuel pressure test and found 57-62 psi. all in all they gave it back to me told me to dump sea-foam in the tank and fill it and drive it. That did not change anything at all. so today i pulled the plugs on 2,4,6 and they were o.o70 and 0.080 so i cleaned them and re gaped them to the 0.060. still did not fix it. tested the icm its good and same with the coil. im at a lose any advice would be helpful. note it only misses when the engine is warmed up and at idle and up to 2000 rpms till its over that and then it does not miss again till you shut it off and restart it after going into the store.
thanks in advance.

 

DarkRose, did you ever find out the problem? Im having the exact same symptoms as you, except the no start. My misfire will happen when the weather is warmer, it runs great when below 15 degrees F.

 

I would check fuel by doing a fuel pressure leak down test. Rent a fuel pressure gauge at auto zone and test at the schrader valve which is at the rear of the engine bay with key on engine off. Pressure should go up to 60 - 65 psi and drop to no less than 55 psi after 10 minutes. If it fails then your problem is either your fuel spider or fuel pressure regulator or it could be your fuel pump. To pinpoint where your problem could be would be by testing fuel pressure at the fuel filter. If it passes the fuel pressure leak down test at the fuel filter your problem is in the plenum. If it fails, most likely a fuel pump.