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1994 Explorer Sport O2 low voltage

markhenry63

Member
Joined
January 27, 2013
Messages
19
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Year, Model & Trim Level
1994 Ford Explorer
I've got a 94 Ford Explorer that has STFTRM1 number that jumps to 43 and sticks until the engine warms up then it starts tracking normally with STFTRM2.
The B1 o2 sensor only ranges from .00-.03VDC while B1 o2 sensor is ranging normally from .01-.09 even after the engine is warm.
I always get a 332 error some time after going down the road (usually 1-3 miles depending on outside temp). The code clears after engine off/on but sets sooner once engine is warm.
All other readings from the OBD appear normal. Both o2 sensors were replaced at the same time due to low reading for both about 12 months ago.
During warm idle the engine intermittently "putters" but there are no misfire codes.
One thing I've noted, ST FTRM1 will regularly go to 43% and hang there even though pulse width doesn't always reflect the level.
While monitoring, it will suddenly start tracking with ST FTRM2 and PW1 will return to track PW2.
O2SEN1 always reads lower and has a smaller range than OSSEN2 at any temperature or throttle position.
I consistently still get EGR flow insufficient CM 332...Not sure how to troubleshoot that one further.
The source and monitor tubes for the DPFE sensor are clear,
Old EGR valve was clear with intact diaphragm but I changed it anyway since it was original and I had it off.
While I had EGR off, I spray cleaned EGR and DPFE tubes with carb cleaner to insure no fowling in the orifice (no change to 332 CM code)
EGR Control Valve was failed (read high resistance across the solenoid)
IAC solenoid read open (swapped out)

I've driven several trips (one 1500 and several 500 mile) after these repairs and it seems to run good around 70mph/2000rpm and I get right at 19mpg.
My usual daily driving to work is only 7-8 miles round trip so barely gets warmed up by the time I stop on each trip.

Here are some the running results from the OBD testing and monitoring. I only included a few frames so you can see the variations on the different sensors.

Reset PCM (disconnected battery and left hood light on).
1994 Ford Explorer X=4.0L Auto (5 Spd M5OD)

DTCs (Codes)

111 ECM

Sys Pass Code No Faults Detected During
KOEO Test

KOEO
------------------------------
111 ECM
Sys Pass Code No Faults Detected During
KOEO Test

KOEO
------------------------------
111 ECM
Sys Pass Code No Faults Detected During
KOEO Test
MEMORY
==============================
DTCs (Codes)
332 ECM
EGR Flow Insufficient
Sample Frames while running after warm-up
FRAME: 3 TM: 0.5

BOO/BPP Off
CANST PURGE On
ECT(V) 0.6
ECT(°F) 197
ENGINE SPD 1564
EVR(%) 0
FUELPW1(mS) 3.6
FUELPW2(mS) 3.6
IAC(%) 43
IAT(V) 1.8
IAT(°F) 118
LOOP STATUS Clsd
MAF(V) 1.0
O2SEN 1(V) 0.21
O2SEN 2(V) 0.70
SPARK(°) 26
ST FTRM1(%) -1
ST FTRM2(%) -1
TP MODE P/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 0
WOT A/C OFF Off

------------------------------

FRAME: 4 TM: 0.6

BOO/BPP Off
CANST PURGE On
ECT(V) 0.6
ECT(°F) 197
ENGINE SPD 1564
EVR(%) 0
FUELPW1(mS) 3.6
FUELPW2(mS) 3.6
IAC(%) 43
IAT(V) 1.8
IAT(°F) 118
LOOP STATUS Clsd
MAF(V) 1.0
O2SEN 1(V) 0.21
O2SEN 2(V) 0.70
SPARK(°) 26
ST FTRM1(%) -1
ST FTRM2(%) -1
TP MODE P/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 0
WOT A/C OFF Off

------------------------------

FRAME: 5 TM: 0.8

BOO/BPP Off
CANST PURGE On
ECT(V) 0.6
ECT(°F) 197
ENGINE SPD 1564
EVR(%) 0
FUELPW1(mS) 3.6
FUELPW2(mS) 3.6
IAC(%) 43
IAT(V) 1.8
IAT(°F) 118
LOOP STATUS Clsd
MAF(V) 1.0
O2SEN 1(V) 0.21
O2SEN 2(V) 0.70
SPARK(°) 26
ST FTRM1(%) -1
ST FTRM2(%) -1
TP MODE P/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 0
WOT A/C OFF Off

------------------------------

FRAME: 6 TM: 0.9

BOO/BPP Off
CANST PURGE On
ECT(V) 0.6
ECT(°F) 197
ENGINE SPD 1520
EVR(%) 0
FUELPW1(mS) 3.6
FUELPW2(mS) 3.6
IAC(%) 43
IAT(V) 1.8
IAT(°F) 118
LOOP STATUS Clsd
MAF(V) 1.0
O2SEN 1(V) 0.00
O2SEN 2(V) 0.40
SPARK(°) 26
ST FTRM1(%) 1
ST FTRM2(%) 1
TP MODE P/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 0
WOT A/C OFF Off

------------------------------
Any/All help/insight is appreciated!!
Sincerely,
Mark
 
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Centaurious

Well-Known Member
Joined
April 28, 2015
Messages
433
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125
City, State
Pensacola FL
Year, Model & Trim Level
1994 Explorer Sport
Have you considered swapping the O2 sensors side to side and seeing if the error moves from one bank to the other? If it does the O2 sensor is faulty, if not your problem is elsewhere.
 
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