4.3l engine data and help on diagnosis.
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
|| Freeze frame DTC
|| Fuel system status
|| Closed-loop, using oxygen sensor feedback to determine fuel mix
|| Calculated load value
|| Engine coolant temperature
|| Short term fuel % trim - Bank 1
|| Long term fuel % trim - Bank 1
|| Short term fuel % trim - Bank 2
|| Long term fuel % trim - Bank 2
|| Intake manifold absolute pressure
|| Engine RPM
|| Vehicle speed
|| Mass air flow rate
|| Absolute throttle position
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.
Upper and lower intake manifold gaskets(which were obviously blown and leaking coolant)
O2 sensors(before the cat, ones after cat were replaces no to long ago)
Throttle position sensor
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.