Hi,
I am new to the forum and have a specific problem with my truck that I have been working on for months. Here is the vehicle description, problem description, data, and parts that have been replaced.

Vehicle: 2000 Silverado 1500, 4.3l v6, 190k miles


Problem description: Starts and idles fine, but stumbles for about 5-10 seconds after I give it gas. As soon as it recovers, the truck runs fine. Occurs when engine is hot or cold. Throwing codes 171 and 174(lean fuel banks 1 and 2). Getting about 16MPG, expecting to get 20mpg.


Data: I have a OBDII to USB interface and OBDWiz software on a laptop that collect live data. Here are the reports:


Service $02 - Freeze Frame Report (when code is thrown)
Date: 6/27/2012 1:19:52 PM
PID Description Value Units
0x02 Freeze frame DTC P0171
0x03 Fuel system status Closed-loop, using oxygen sensor feedback to determine fuel mix
0x04 Calculated load value 23.92 %
0x05 Engine coolant temperature 188.6 F
0x06 Short term fuel % trim - Bank 1 15.62 %
0x07 Long term fuel % trim - Bank 1 23.44 %
0x08 Short term fuel % trim - Bank 2 20.31 %
0x09 Long term fuel % trim - Bank 2 23.44 %
0x0B Intake manifold absolute pressure 12.47 PSI
0x0C Engine RPM 1582.5 RPM
0x0D Vehicle speed 54.68 MPH
0x10 Mass air flow rate 5.17 lb/min
0x11 Absolute throttle position 36.08 %







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The above charts(except the Freeze Frame) show a trip through to to corner store about 2 mile away(on a hwy) with the engine already warm. Each chart is synced with time and the stats are for this same trip. The Short Term Fuel Trim(STFT) mean is above 10, which causes the 171 and 174 codes. However, O2 sensor mean volt is .5 and .4, which I believe good. Thus, I do not think there is actually a lean condition here. Thus I am stumps to what is causing the codes and presumably, the stumbling.



Parts replaced:
Upper and lower intake manifold gaskets(which were obviously blown and leaking coolant)
EGR valve
Map sensor
O2 sensors(before the cat, ones after cat were replaces no to long ago)
MAF sensor
Throttle position sensor
fuel filter
Fuel pump(including sock filter)
Cleaned injectors(took the spider out and cleaned)
Cleaned entire intake and throttle body.


I have checked for vacuum leaks extensively by spraying card cleaner around the engine and cannot get the rpms to budge or the O2 sensor data to show any deviation.


I was thinking a possibility is that both cats are clogged. The coolant leak was going into cycliders and out the exhaust. However, I would expect data to indicate this. The freeze Fame data for when the codes are thrown shows 12.47psi at 54mph.


I am running out of ideas. Any help would be appreciated.


Randy