Need help with stats (Fuel Trims) w/ P0300 code
 

1995 Chevy Blazer 4Dr 4x4 4.3L V6 RPO=L35 Package - OBD=1.5 (Certified OBD1 w/OBD2 connection)
Mileage: 166,000
Problem: Rough at Idle, Poor Gas Mileage - Runs smooth at higher speeds and RPMs
Code: P-0300 - Random misfire detected
No other codes active

What I have done to date:
Replaced Plugs, Wires, Dist. Cap & Rotor
Cleaned EGR valve (Definitely Clogged - P0401 code now resolved)
New Air Filter
New Gas Filter
Pre-Treated oil then Fluid & Filter w/Lucas
Seaform'd Fuel System & Throttle body
2nd round of Injector cleaner - 30 days later

Done by Previous owner on February 2, 2018***:
New Gas Tank
New Fuel Sending Unit
New Vent Valve
Repaired fuel lines
*** Note: I trust these guys as far as I can throw them. The gas tank has horrible fumes when filled past halfway. I am going to have to investigate the pump seal at some point.

SCAN TOOL USED: Actron CP9145
RESULTS
Test at Idle @ varies between 750 -to- 850 RPM
MIL Status = ON
Absolute (ABSLT) TPS = varies between -0% -to- 5.1%
Calculated Load = varies between 3.3 -to- 7.3
MAP (“HG) = varies between 13.3 -to-16.2
Coolant = 127 °F
Intake Air Temp (IAT) = 86 °F
Ignition Advance (IGN ADV) = varies between 0 – 23.5

Short Term Fuel Trim 1 (ST FTRM1) = varies between -42.2 -to- -55.5 (@ 2500 RPM = -39 -to- -40)
Short Term Fuel Trim 2 (ST FTRM2) = varies between -39 -to- -52.3 (@ 2500 RPM = -39 -to- -40)
Long Fuel Trim 1 (LT FTRM1) = 4.7% (@ 2500 RPM = -0%)

Fuel Sys 1 = CLSD
Fuel Sys 2 = n/a

02S11 = varies between .1 -to- .780
02S12 = varies between .05 -to- .09


************************************************** ************************************************** **********
As I understand it, the Short Term Fuel Trims are way out-of-whack indicating a rich condition.

Things I know to check are (but what is most likely?)
MAP Sensor – Cleaned today. It looked good and cleaning helped a little
02 Sensor
Exhaust Issue - Has near new Exhaust, not sure about CAT Converter
Leaking Fuel Injectors – Possibly replace Spider CMFI
Bad Fuel Pressure Regulator
EVAP Issues
High Fuel Pressure

If you could share your opinion, that would be great!

I am leaning toward a fuel system issue and possibly a new spider. For now I am going to follow this Sticky Thread: https://blazerforum.com/forum/2nd-ge...eakdown-88305/

Thanks in Advance!

Suspect a faulty FP regulator. Watch this video for FP leak down testing :

Schrader valve cross threaded :(
 

So after much research, I have determined that I am running excessively rich . Determined not only by the fuel trim levels but also the heavy carbon coming out of the exhaust and high carbon deposits and other internal sensors to the manifold, the EGR valve, the map sensor, etc. Of course I got my new Actron CP 7818 fuel tester yesterday only to find that the Schrader valve on my fuel rail is cross-threaded therefore it will not screw on; and I don't have that die. How difficult is this to replace?

I noticed that your coolant was at 127°F. If that's the normal operating temp your ecm sees then it's definitely throwing your fuel trims out of spec. A bad temperature sending unit can cause all sorts of hell. Have a look at it. Wouldn't hurt to cross it off the list of possibilities.

Nice Catch GB2002!

I will check the coolant system as well.

Thanks.

GB2002, The 127°F was measured when the truck was just started and rather cool. I drove the truck today on a 5 mile trip it got up to 165°F. Normal Temp is 195°F Tomorrow have have a longer trip so we see the results afterwards, but I think I am running in OK temp, but I'll verify.