marlboroa

Hello, The other day my truck went from running fine to knocking and lost power while going down the road. I did a cold start this morning and #4 is cold if i touch the exhaust manifold. all the others warmed up like usual the knocking was still there. just a few minutes ago i let i warm up all the way and the knocking seems to have went away for now but still runs bad and misses. Heres the scan tool data i got. Its a 2002 4.8 silverado 2wd 200,000 miles

fuelsys2 CL
load_pct 1.2
ETC (F) 181
SHRTFT1 22.7
LONGFT1 25.0
SHRTFT2 30.5
LONGFT2 25
FRP (psi) N/A
MAP (KPa) 38
RPM 539
SPEED 0
SPARKADV 25
IAT (F) 61
MAF LB/MIN 0.435
TP (%) 0
AIR_STAT N/A
02SLOC B1S12--B2S12
02B1S1 (v) 0.090 this will go up to 0.810
02B1S2 (v) 0.835 this will go down to .01 but takes a while to start dropping
02B2S1 (v) N/A
02B2S2 (v) N/A
02B3S1 (v) 0.110 goes to 0.795
02B3S2 (v) 0.875 goes to 0.865
02B4S1 (v)
02B4S2 (v) N/A
OBDSUPPORT OBDII
02SLOC N/A
PTO No Act
And the rest of the data was all N/A

Do i need to run the truck longer to get a reading on the N/A 02 sensors or are they bad? Any help is greatly appreciated

EDIT: I went and put a higher octane gas in it and let it run for about 20 minutes and then drove it and it seems to be running fine. I really would like to know what caused the initial problem in case it returns.

chem_man

Thanks for the data, but what we really need from you in order to better assist you are the OBDII codes that are in the PCM - all the codes - pending, current, historical.

It's obvious from the fuel trims that something is amiss and if your Check Engine Light is not illuminated or flashing, you better see if the lamp behind the instrument panel for the Check Engine Light is burned out.

Based on your observation that the exhaust manifold by the #4 cylinder is significantly cooler, I would say that no combustion is occurring there. Possible causes - bad ignition coil, bad spark plug, bad fuel injector, bad wiring to the fuel injector, bad wiring to the ignition coil, or a bad #4 spark plug wire.

For what it's worth, your fuel trims are indicating that the PCM believes that the engine is running really lean so it is increasing the amount of fuel that is spraying into the cylinders.

Good Luck!