How to: 2000 SOHC PCM Data

This post will be a "work in progress" description of things I have learned about the operation of the PCM. The initial things learned are from analyzing performance changes resulting from my throttle body and MAF sensor modifications. The data was obtained using a Windows based Dyno-Scan scanner, an AutoMeter wideband Air/Fuel ratio meter, the stock instrument cluster, a combination ATF/engine oil temperature gauge, and personal observations. It is my opinion that a scanner and A/F ratio meter are the two most useful "tools" in determining what's happening in an engine. With today's fuel injected engines that rely heavily on electronics, these tools greatly simplify identifying degraded and failed components.

Abbreviations:
A/F: Air/Fuel ratio
BTDC: Before Top Dead Center
BX: Bank #
BX-SX: Bank #-Sensor #
CEL: Check Engine Light
DTC: Diagnostic Trouble Code
ECT: Engine Coolant Temperature
FMEM: Failure Mode & Effects Management
hr: hour
KAM: Keep Alive Memory
lb: pounds
LTFT: Long Term Fuel Trim
MAF: Mass Air Flow
MAFS: Mass Air Flow Sensor
MAP: Manifold Absolute Pressure
MIL: Malfunction Indicator Light
O2S: Oxygen Sensor
OBD: On-Board Diagnostics
PCM: Powertrain Control Module
rpm: revolutions per minute
STFT: Short Term Fuel Trim
SX: Sensor #
TPS: Throttle Position Sensor (1.0 volts at closed throttle, 4.7 volts at WOT)
v: volts
WOT: Wide Open Throttle

Definitions:
Bank 1: cylinder bank containing #1 cylinder (passenger side)
Bank 2: cylinder bank not containing #1 cylinder (driver side)
Closed Loop: PCM utilizes O2S data to control fuel mixture
KAM reset: battery disconnected for at least 5 minutes
Open Loop: PCM utilizes MAFS, TPS, engine rpm to control fuel mixture

Observations:

Fast idle: (1400 to 1500 rpm) lasts until ECT exceeds 62 degrees, or for approximately 3 seconds after engine start if ECT is greater than 62 degrees
Moderate idle: (1000 gradually decreasing to 850 rpm) lasts until ECT exceeds 120 degrees
Normal idle: 750 gradually decreasing to 700 rpm as ECT increases to normal

LTFT can 31% in 1.0 seconds
STFT can change 25% in less than 0.7 seconds

LTFT is computed by the PCM and stored in KAM for the next engine cycle. It will not change while the engine is idling. When engine speed exceeds 3200 rpm, LTFT becomes 0%. When A/F ratio is lean, LTFT is positive. When A/F is rich, LTFT is negative.

Engine started & idled with A/F ratio = 16.0:1, LTFT = +25%, STFT = +42%, no DTC
idled with A/F ratio = 14.7:1, LTFT = +10%, STFT = +42%, no DTC

Useful information:
MAFS dirty/degraded: negative LTFT at idle, positive LTFT at high engine speeds
Disconnecting MAFS initiates FMEM. In FMEM mode, air flow is inferred by using rpm and throttle position instead of reading the MAF sensor.
Theoretical best fuel economy A/F ratio: 15.4:1
Theoretical maximum power A/F ratio: 12.6:1
Measured maximum power A/F ratio: 11.7:1
Ignitable fuel mixture A/F ratio range: 11.3:1 to 21.0:1 (theoretical limits according to Bosch documentation, while experimenting I have unintentionally run my engine for brief periods at light load with A/F ratio meter indicating as low as 10:1)
O2S degrade with age, new: 0.95 to 0.07 volts, aged: 0.83 to 0.09 volts
V6 firing order: 1-4-2-5-3-6

The following is a list of the parameters that my scanner determined are available via the OBD port:

Absolute Throttle Position: mine varies from 19% at closed throttle to 92% at WOT, PCM reads the TPS min & max and stores value for next engine cycle, disabling KAM forces PCM to establish new limits
Air Flow Rate From MAF: PCM computes lb/hr based on MAFS output voltage, typical stock 55mm MAFS output: 0.8v@550rpm, 1.0v@1000rpm, 1.25v@1500rpm, 1.4v@2000rpm, 1.55v @2500rpm, 1.65v@3000rpm, 1.9v@3500rpm, 2.1v@4000rpm
Air Flow Rate From MAP
Average Economy
Average Economy 2
Average Speed
Battery Voltage: no valid data
Calculated Load
Distance Traveled
Drive Time
Engine Coolant Temperature: change in sensor value has significant impact on idle speed
Engine RPM: speed limited to 6188 rpm, for constant & gradual speed change good correlation with tachometer, for throttle "blip" tachometer displays significant lag then overshoot
Fuel Cost
Fuel Cost 2
Fuel Rate
Fuel Rate 2
Fuel Used
Idle Percent
Idle Time
Ignition Timing Advance: in degrees BTDC, mine varies from 8 to 42, typically 15 @ 700, 18 at 1000, 28 at 1800 rpm, 34 at 2400, 37 at 3800
Instant Economy
Instant Economy 2
Intake Air Temp: change in sensor value has minor impact on idle speed
Long Term Fuel Trim B1:
Long Term Fuel Trim B2
Long Term Fuel Trim B3: no valid data
Long Term Fuel Trim B4: no valid data
O2 Sensor B1-S1
O2 Sensor B1-S2
O2 Sensor B2-S1
O2 Sensor B2-S2
Short Fuel Trim B1-S1
Short Fuel Trim B1-S2
Short Fuel Trim B2-S1
Short Fuel Trim B2-S2
Short Term Fuel Trim B1
Short Term Fuel Trim B2
Short Term Fuel Trim B3: unknown meaning, range +100% to -100%
Short Term Fuel Trim B4: no valid data
Vehicle Speed

At my convenience I'll be adding comments to the above parameters.

I read on the forum that the 5R55E transmission reports it's ATF temperature to the PCM. I was disappointed when ATF Temperature was not one of the above parameters. I added an ATF temperature sender and mounted a gauge in a pillar pod to provide the data.

Bank 3 STFT?

Does anyone know anything about Short Term Fuel Trim (STFT) for Bank 3? Obviously, I don't have a "T6". I only have Banks 1 & 2 but my PCM generates STFT for Bank 3 and makes it available on the OBD bus. It doesn't correlate with any of the fuel trims (long term or short) for Banks 1 & 2. Any ideas?

The signal for trans temp should be there somewhere. Have you tried using a different device to get it? I can get it on my v8 with a scan gauge II, and with my x-cal 2.

V8 vs SOHC

techieman33 said:

The signal for trans temp should be there somewhere. Have you tried using a different device to get it? I can get it on my v8 with a scan gauge II, and with my x-cal 2.

Click to expand...

No, I haven't tried any other scanner for trans temp. It's in the list of parameters supported by Dyno-Scan (as are many others not listed in my post) but when I connect to the OBD port it's not available. I wonder if it's available from the V8 PCM and not the V6 SOHC.

Do you get any data with your scanner for Battery Voltage?

I'm pretty sure I do it's been a while since I've recorded any logs. The list is miles long though so I'm sure the voltage is in there somewhere.

I noticed you mentioned MAF sensor dirty due to negative trims, please note I would only follow that on a stock vehicle. If you have a tuned vehicle I would verify trims before trouble shooting. Just so you arent chasing a ghost. -j

From tsb

jah81592 said:

I noticed you mentioned MAF sensor dirty due to negative trims, please note I would only follow that on a stock vehicle. If you have a tuned vehicle I would verify trims before trouble shooting. Just so you arent chasing a ghost. -j

Click to expand...

Thanks James. I got that information from a Ford technical service bulletin. I moved the entry from "Observations" to "Useful Information" since I have not actually observed it. Also, I don't plan to post any data on this thread that does not apply to the stock SOHC configuration. I don't want to mislead someone who is not familiar with my unorthodox modifications.

pcm?

I got a pcm from the junkyard and wondered if you can send them to be flashed? From what I understand of flashing the pcm, there is dyno testing involved to fine tune it. I could misunderstand it. I don't know if it's possible but thought I might try since I pulled the unit for free.
Thanks

pcm tune/reprogram

any thoughts?

Custom tune & reflash

See the following thread for one way to obtain a custom tune: Custom tune by Henson

I doubt that any reputable tuner would provide a custom tune without the ability to test it on your vehicle.

Your vehicle is PATS equipped. Unless the salvage yard PCM is reprogrammed to defeat PATS or coded for your keys it will not allow the engine to start.

DynoScan

2000StreetRod I see this thread is a few years old.
But in the of chance you are still around and still have the DynoScan
here goes.

I too have a DynoScan and I too have the same exact issue you saw with the
data. (missing data on a few items and a data item with no apparent use)
I was wondering if you saw something this next item.
I see the same data on two of the items.
Short Fuel Trim B1-S2
Short Fuel Trim B2-S2
Also they are stuck reporting one value (92.2%)
Did you see this or have anything to share on them?
I have contacted the Auterra. They may never respond
to this exactly but did say to uncheck (fast data) and (CAN)
in the Tools/Options menu. It made no difference.
Scott