Today I was sitting at a light and my engine light came on, sure enough, I got home and plugged up my scanner, and it was random/multiple misfire. I took these readings off of the scanner. All readings are at time of misfire.

ABSLT TPS 0.0%
565 RPM
Load 2.7%
MAF Flow 4.82 (gr/sec)
MAP 40 kpa
Coolant temp 190
ST FTRM1 0.0%
LT FTRM1 9.3%
ST FTRM2 0.0%
LT FTRM2 0.0%
0 MPH
Fuel sys 1 closed
Fuel sys 2 closed

Are all of these normal?

I've had this random misfire on and off for about 3 months now. It started after my radiator cracked and my truck overheated. Replaced ignition coil, distributor, cap, rotor, plugs, and wires. It went away and my car ran perfect when my intake gasket was later blown. Replaced the spider injector, thermostat, and the gasket and my misfire was there again. Cleaned EGR Valve, ran seafoam through my truck, then replaced the fuel filter and crank sensor, problem went away for about 2 days and came back. I cleared the code about three weeks ago, then my ignition coil went out, I replaced that about a week ago, now the code has come back. My truck starts hard when it is warmed up, kinda bogs a little before it starts all the way, but starts great if it's had a chance to cool down. Sometimes it bogs down a little in reverse too, or if I'm in park and rev the engine, it will dip below 350 RPMs when it comes down sometimes. I have another truck that runs good aside from the engine knock that I can take parts off of. I know no one will have a magic answer, but this misfire is killing me, please help.

I also thought I should mention I have a spectre CAI if that affects any of the readings above.

 

Long Term fuel trim on Bank 1 is getting excessively rich. You probably have an air leak somewhere on the driver's side of the engine. Spray some brake cleaner or carb cleaner, etc, around the intake manifold & note any changes in fuel trim or RPM - intake gasket could be leaking again.

Wouldn't hurt to spray clean the MAF sensor either.

Looks like you've replaced everything normally associated with a 0300 ... so something isn't right here ...

Keep us posted.

 

I took the brand new MAF sensor out of the other truck to see if it would change anything, nothing. I sprayed carb cleaner anywhere I could get it and there was no noticeable change. My scan tool only read the freeze frame from the computer, so I can't get live data. I took a video to try to show my RPM dip, which of course didn't happen since I was recording it, but it does do it slightly when I put it in reverse. I had my scan tool hooked up as well, and you can see the blinking engine light in the video, but as that happened it pulled a P0306 code. No freeze frame.

Blazer misfire - YouTube

 

with the p0306 code then its your 6th cylinder that's misfiring cause of the 6 at the end of the 300 code. like a p0301 is the first cylinder and so on. i also had the p0300 but mine was cause of cheap plugs.

 

Alright I got another freeze frame while driving, it was raining if that affects anything

Abslt tps 17.6%
1563 rpm
Load 16%
maf flow 26.86 (gr/sec)
Map 59kpa
Coolant 134
St ftrm1 5.4%
lt ftrm1 11.7%
st ftrm2 4.6%
lt ftrm2 7.0%
8mph
Fuel Sys 1 & 2 closed*

 

I'm driving this thing off a bridge, whatever is left is up for grabs.

I had two shops tell me it was my injectors. I had them replace those. I had an oil leak at the lower manifold so i had them replace that gasket too, along with the distributor gear. Ran fine for 3 days and now it's back to missing again. Although my hard starting problem went away so at least SOMETHING got fixed. And maybe it's just me but I think my brakes work better...

I'm definitely running out of ideas here. My exhaust leak sound was also gone for a short while after the job was done, but slowly came back the next day.

1 & 6 are the cylinders that misfire the most.

 

Could have some leaky intake manifold gaskets, or (going out on a limb here) possibly a failing crank position sensor - but usually that will result in a no-start condition.

I feel your pain. I had the same problem after spending thousands over the course of 2 years fixing a myriad of other problems ranging from the entire front end, y-pipe and cat, express UP drivers window ( the Guillotine ), and headlights that just quit at 9pm on a busy road, just to name a few off the top of my head. I threw in the towel after the misfire. My avatar is how it sits today - I didn't have the heart to pass the curse on to anyone else.

Never did figure out what it was, but when I was installing that engine in the '89 Blazer I found the intake manifold gaskets in HORRIBLE condition - cracked & split wide open ... and the worst of it happened to be around those 2 same cylinders intake ports.

Just food for thought. Good luck!

 

last time I did a tune up on my truck I accidentally broke the plastic clips holding the plug wires down, and they touched, creating a crossfire ie caused a P0300 code.