Join Date: Jun 2010
Location: Fraser Valley, BC, Canada
Drives: Caribou, Otter, Buffalo
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OBDii Diagnostics with SCANNER
The screen shots are the basic required information of an OBDII compliant vehicle.
The screens will be noted left to right from top to bottom.
the screen with the Six dials contain;
Throttle .. Vacuum
Tachometer .. Speedo
Intake Air Temp .. Coolant Temp
The second screen contains the
air (MAF)......fuel (adjusted for 14/1 ratio, LTFT)
The first dials of value are the IAT and the Coolant, they must be equal (ambient) when the engine is cold..
Second value (TPS), engine off, key on, throttle depressed slowly must register on gauge with a gradual sweep with no jitter/jumps.
On cold start the ECU checks the coolant temp and if <180* will initiate rich injection and open ISC (idle control), colder the value the richer the injection(longer pulse).
As the coolant temp increases the ECU commands the ISC and Injection pulse to reduce fuel/air, lowering RPM to +/-800.
On reaching coolant temp >170* the ECU obtains CL (closed loop) and allows the O2 S1 to control the data based on the amount of unburnt oxygen in the exhaust prior to CAT.
In order to achieve the stoic 14.1/1 AFR ratio, the ECU considers the coolant temp + MAF + O2 + TPS.
The second screenshot displays the MAF value. Once running the ECU adjusts the fuel (STFT) based on the collected data, the STFT fluctuates to quickly to be useful at this point so the LTFT is required The closer to 0.0 the better, +/-10 requires attention, and above serious investigation. The system will trigger a CEL somewhere close to 15% and above..
It is important to recognize the O2 values must switch rapidly and even top to bottom. If the readings are consistently High(rich mixture) or Low(O2 sensor is biased or sees an O2 leak) and if slow has become lazy..
It is important to know that the system cannot have any illegal air leaks, either post MAF>prior combustion chamber, or post combustion chamber>pre CAT. Hence the requirement for the Vacuum gauge. The S2 has no bearing on the fuel air ratio and the sensor only monitors the values exiting the CAT
Remember switching/replacing parts and guessing just wastes time and $$$.....
The trick is to get the engine working correctly.
Hope this has given you a start......Philip
Last edited by aquanaut20; 08-10-2011 at 07:14 PM.