Pirate 4x4 banner

LQ4 losing power under load

19K views 53 replies 11 participants last post by  Team208Motorsports 
#1 · (Edited)
The 2006 LQ4 in my rig has recently experienced power loss under heavy load conditions. It happens on ledges and hard 4wd 4th gear pulls moving about 35mph. Any time the tires meet resistance under heavy throttle it happens. When it happens, the motor de-revs even under constant open throttle. I can confirm this with a scan tool. When "calculated load" reaches 100%, power loss occurs.

This began happening shortly after I had the PCM reprogrammed from an express van MAF to a truck MAF. The tuner insists it is programmed for the correct mass air sensor. I am also running a brand new Delphi MAF after trying two used ones.

Periodically the PCM is throwing lean codes that I think may be related. I do not have any vac leaks and I have a new fuel pump and filter. It is converted to DBC.

What could cause sudden power loss under load? It seems uncanny that the problem happens immediately when the scan tool calculated load value hits 100% while driving.
 
#2 ·
The engine has parameters that defuel the engine to protect it. 100% load may well be one of those conditions and it sounds like your tuner changed something. Different mafs do have different table values that convert the Maf electrical outputs to air values but that should not have the effect you are describing if the tuner just changed the Maf table.
 
#3 ·
I agree make sure your tune is correct for the maf values. If you change the intake tube for example it will change what the MAF see's and could be getting more air then the PCM thinks its getting hence it running lean.
 
#6 ·
LQ4's don't have VVT....
 
#5 ·
If you are getting lean codes, it's most likely running lean. Lean condition will also cause it to loose power under high loads.

Put a pressure gauge on the motor so you can see it from within the rig and take it for a drive. Verify it never drops below 58 psi.

Changing the MAF tables and the problem could just be coincidental. The actual issue was probably already there before, but since the van MAF is smaller, wasn't showing an issue until you went to the larger truck MAF/Tune.

Post up some live data of when it's happening. That will help us, too.

EDIT: What's your o2 voltage under load, when it's loosing RPM's?
 
#7 ·
Fuel pressure is good. That was the first thing we checked. I am also running a fresh vette filter and walbro 255 now.

This morning we got some gopro videos of live data on the scanner while the power loss is occurring. I will post those vids ASAP. I'll also post the data log as soon as we can get it off the scan tool.
 
#8 ·
You checked fuel pressure WOT, under heavy load? Or idling in the garage? Two very different situations.... :)
 
#10 ·
Awesome :D
 
#11 ·
What's the actual DTC's your seeing?
 
#14 ·
Circuit Description


The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals without oxygen sensor input. During Closed Loop, the PCM adds oxygen sensor inputs and level of purge to calculate short and long term fuel trim adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. The values for the short term fuel trim change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes course adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The PCM selects the cells based on the engine speed and engine load. If the PCM detects an excessively lean condition, DTC P0171 or P0174 sets.

DTC Descriptors


This diagnostic procedure supports the following DTCs:
• DTC P0171 Fuel Trim System Lean Bank 1
• DTC P0174 Fuel Trim System Lean Bank 2

Conditions for Running the DTC


• DTCs P0053, P0054, P0059, P0060, P0101, P0102, P0103, P0106, P0107, P0108, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0200, P0300, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P1133, P1134, P1153, P1154, P2A01, or P2A04 are not set.
• The engine coolant temperature (ECT) is between −40 to +140°C (−40 to +284°F).
• The intake air temperature (IAT) is between −20 to +152°C (−4 to +304°F).
• The manifold absolute pressure (MAP) is between 15–105 kPa (2.2–15.2 psi).
• The vehicle speed is less than 132 km/h (82 mph).
• The engine speed is between 400–6,500 RPM.
• The barometric pressure (BARO) is more than 74 kPa (10.7 psi).
• The mass air flow (MAF) is between 1–250 g/s.
• The fuel level is more than 10 percent.
• The throttle position is less than 90 percent.
• This diagnostic runs continuously once the above conditions are met.
.

Conditions for Setting the DTC


The long term fuel trim weighted average value is more than a calibrated value for 2 seconds.

Action Taken When the DTC Sets


• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC


• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids


• Excessive resistance in the fuel injector control and/or the ignition 1 voltage circuits may cause the following symptoms:
- A lean condition
- Misfire
- Rough idle
- Refer to DTC P0200 .

• The system may become lean if an injector is not suppling enough fuel.
• A lean condition could be present during high fuel demand.
• Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .



Step
Action
Values
Yes
No

1
Did you perform the Diagnostic System Check –Vehicle?

Go to Step 2



Go to Diagnostic System Check - Vehicle


2
Are any DTCs other than DTC P0171 or P0174 also set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3




3
1. Install the scan tool.

2. Start and idle the engine at the normal operating temperature in Closed Loop.

3. Record the long term fuel trim.

4. Turn OFF the engine.

5. Turn ON ignition, with the engine OFF.

6. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.

Does the scan tool indicate that the long term fuel trim is greater than the specified value?
24%
Go to Step 4



Go to Diagnostic Aids

4
1. Operate the engine at idle.

2. Observe the HO2S parameters with a scan tool.

Does the scan tool indicate that the parameter is within the specified range and fluctuating?
200–800 mV
Go to Step 5



Go to Step 6




5
1. Turn OFF the engine.

2. Visually and physically inspect the following items:

• The vacuum hoses for splits, kinks, and proper connections—Refer to Emission Hose Routing Diagram .


• Ensure that the vehicle has sufficient fuel in the tank. If the fuel pressure is too low, this DTC may set. Refer to Fuel System Diagnosis .


• Fuel contamination—Refer to Alcohol/Contaminants-in-Fuel Diagnosis .


• Any lean fuel injectors—Refer to Fuel Injector Balance Test with Tech 2 .


Did you find and correct the condition?

Go to Step 8



Go to Step 7




6
1. Turn OFF the engine.

2. Inspect the heated oxygen sensor (HO2S) for proper installation.

3. Verify the electrical connectors and the wires are secure, and not contacting the exhaust system.

4. Test for continuity between the HO2S signal circuit and the low reference circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs .


Did you find and correct the condition?

Go to Step 8



Go to Fuel System Diagnosis


7
1. Operate the engine at idle.

2. Inspect for any missing, loose, or leaking exhaust components forward of the HO2S.

3. Inspect for vacuum leaks at the intake manifold, throttle body, and injector O-rings.

4. Inspect the air induction system and the air intake ducts for leaks.

5. Inspect the secondary air injection (AIR) system for leaks, improper air delivery, and for the shut-off valves not closing.

6. Inspect the crankcase ventilation system for leaks. Refer to Crankcase Ventilation System Inspection/Diagnosis .


7. The evaporative emission (EVAP) lines and components for damage or blockage—Refer to Evaporative Emissions Hose Routing Diagram .


8. Inspect the vacuum brake booster for leaks.

Did you find and correct the condition?

Go to Step 8



Go to Symptoms - Engine Mechanical


8
Important: After repairs, use the scan tool Fuel Trim Reset function to reset the Long Term Fuel Trim.
1. Turn ON the ignition, with the engine OFF.

2. Clear the DTCs with a scan tool.

3. Turn OFF the ignition for 30 seconds.

4. Start the engine.

5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2



Go to Step 9




9
Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK
 
#16 ·
Recorded data from my scan tool posted for heeper...



2006 Chevrolet Express 2500 U = 6.0
Without TAC
I/M Monitors
Since DTCs Cleared
Misfire Monitor ok
Fuel System Mon ok
Comp Component ok
Catalyst Mon ok
Htd Catalyst n/a
Evap System Mon ok
Sec Air System n/a
A/C Refrig Mon n/a
Oxygen Sens Mon inc
Oxygen Sens Htr ok
EGR System Mon n/a
=====================
DTCs (Codes)
P0171 MOD $10
Bank 1 System Too Lean
PENDING
TOP REPORTED FIX
1-Replaced Fuel Pump
FREQ REPORTED FIXES
1-Cleaned Fuel
Injectors
2-Replaced Intake
Manifold Gaskets
ALSO REPORTED FIXES
1-Repaired Engine
Wiring Harness
2-Replaced Engine
Wiring Harness
3-Replaced Exhaust
Valves
4-Replaced Fuel
5-Flushed Fuel
System
6-Replaced Mass Air
Flow (MAF) Sensor
7-Replaced Oxygen
(O2) Sensor
8-Repaired Vacuums
Lines
9-Repaired Wire
Harness
---------------------
P0174 MOD $10
Bank 2 System Too Lean
PENDING
FREQ REPORTED FIXES
1-Cleaned Fuel
Injectors
2-Replaced Fuel Pump
3-Replaced Intake
Manifold Gaskets
ALSO REPORTED FIXES
1-Replaced Exhaust
Valves
2-Replaced Fuel
3-Flushed Fuel
System
4-Replaced Mass Air
Flow (MAF) Sensor
5-Replaced Oxygen
(O2) Sensor
6-Repaired Vacuums
Lines
=====================
Record Data
FRAME: -6 TM: -14.4
MIL STATUS On
ABSLT TPS(%) 13.3
ENG SPEED(RPM) 2560
CALC LOAD(%) 21.6
MAF(LB/M) 3.41
MAP("HG) 8.0
COOLANT(°F) 196
IAT(°F) 99
IGN ADV(°) 48.0
ST FTRM1(%) 0.0
LT FTRM1(%) 9.4
ST FTRM2(%) 0.0
LT FTRM2(%) 6.3
VEH SPEED(MPH) 7
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.155
ST FTRM11(%) -71.1
O2S12(V) 0.440
O2S21(V) 0.080
ST FTRM21(%) -87.5
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: -5 TM: -12.0
MIL STATUS On
ABSLT TPS(%) 14.1
ENG SPEED(RPM) 2617
CALC LOAD(%) 22.0
MAF(LB/M) 3.38
MAP("HG) 8.0
COOLANT(°F) 196
IAT(°F) 97
IGN ADV(°) 48.5
ST FTRM1(%) 0.0
LT FTRM1(%) 9.4
ST FTRM2(%) 0.0
LT FTRM2(%) 6.3
VEH SPEED(MPH) 7
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.100
ST FTRM11(%) -79.7
O2S12(V) 0.440
O2S21(V) 0.050
ST FTRM21(%) -92.2
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: -4 TM: -9.6
MIL STATUS On
ABSLT TPS(%) 14.1
ENG SPEED(RPM) 2544
CALC LOAD(%) 21.6
MAF(LB/M) 3.33
MAP("HG) 8.0
COOLANT(°F) 196
IAT(°F) 97
IGN ADV(°) 49.0
ST FTRM1(%) 0.0
LT FTRM1(%) 9.4
ST FTRM2(%) 0.0
LT FTRM2(%) 6.3
VEH SPEED(MPH) 6
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.065
ST FTRM11(%) -89.8
O2S12(V) 0.440
O2S21(V) 0.040
ST FTRM21(%) -94.5
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: -3 TM: -7.2
MIL STATUS On
ABSLT TPS(%) 29.4
ENG SPEED(RPM) 2700
CALC LOAD(%) 42.0
MAF(LB/M) 7.25
MAP("HG) 13.0
COOLANT(°F) 194
IAT(°F) 97
IGN ADV(°) 43.0
ST FTRM1(%) 0.0
LT FTRM1(%) 4.7
ST FTRM2(%) 0.0
LT FTRM2(%) 6.3
VEH SPEED(MPH) 9
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.065
ST FTRM11(%) -88.3
O2S12(V) 0.440
O2S21(V) 0.050
ST FTRM21(%) -91.4
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: -2 TM: -4.8
MIL STATUS On
ABSLT TPS(%) 15.3
ENG SPEED(RPM) 3057
CALC LOAD(%) 18.4
MAF(LB/M) 3.56
MAP("HG) 7.1
COOLANT(°F) 192
IAT(°F) 95
IGN ADV(°) 46.0
ST FTRM1(%) 0.0
LT FTRM1(%) 9.4
ST FTRM2(%) 0.0
LT FTRM2(%) 6.3
VEH SPEED(MPH) 7
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.065
ST FTRM11(%) -89.8
O2S12(V) 0.445
O2S21(V) 0.045
ST FTRM21(%) -93.8
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: -1 TM: -2.4
MIL STATUS On
ABSLT TPS(%) 10.6
ENG SPEED(RPM) 2361
CALC LOAD(%) 18.8
MAF(LB/M) 2.69
MAP("HG) 7.1
COOLANT(°F) 190
IAT(°F) 95
IGN ADV(°) 49.0
ST FTRM1(%) 3.1
LT FTRM1(%) 9.4
ST FTRM2(%) 7.8
LT FTRM2(%) 6.3
VEH SPEED(MPH) 7
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.100
ST FTRM11(%) -83.6
O2S12(V) 0.445
O2S21(V) 0.775
ST FTRM21(%) -67.2
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 0 TM: 0.0
MIL STATUS On
ABSLT TPS(%) 15.3
ENG SPEED(RPM) 2919
CALC LOAD(%) 19.2
MAF(LB/M) 3.55
MAP("HG) 7.4
COOLANT(°F) 190
IAT(°F) 95
IGN ADV(°) 46.5
ST FTRM1(%) 8.6
LT FTRM1(%) 10.2
ST FTRM2(%) 2.3
LT FTRM2(%) 7.8
VEH SPEED(MPH) 9
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.880
ST FTRM11(%) -72.7
O2S12(V) 0.440
O2S21(V) 0.900
ST FTRM21(%) 29.7
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 1 TM: 2.3
MIL STATUS On
ABSLT TPS(%) 41.2
ENG SPEED(RPM) 3129
CALC LOAD(%) 82.4
MAF(LB/M) 18.21
MAP("HG) 23.9
COOLANT(°F) 190
IAT(°F) 95
IGN ADV(°) 28.5
ST FTRM1(%) 2.3
LT FTRM1(%) 4.7
ST FTRM2(%) -1.6
LT FTRM2(%) 7.8
VEH SPEED(MPH) 21
FUEL SYS 1 OPEN1
FUEL SYS 2 CLSD
O2S11(V) 0.880
ST FTRM11(%) -68.8
O2S12(V) 0.440
O2S21(V) 0.070
ST FTRM21(%) 10.9
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 2 TM: 4.8
MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 4229
CALC LOAD(%) 5.1
MAF(LB/M) 1.46
MAP("HG) 3.2
COOLANT(°F) 189
IAT(°F) 91
IGN ADV(°) 48.5
ST FTRM1(%) 0.0
LT FTRM1(%) 11.7
ST FTRM2(%) 0.0
LT FTRM2(%) 7.8
VEH SPEED(MPH) 20
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.055
ST FTRM11(%) -91.4
O2S12(V) 0.435
O2S21(V) 0.020
ST FTRM21(%) -96.9
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 3 TM: 7.7
MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 2647
CALC LOAD(%) 7.5
MAF(LB/M) 1.13
MAP("HG) 4.7
COOLANT(°F) 190
IAT(°F) 91
IGN ADV(°) 1.5
ST FTRM1(%) 0.0
LT FTRM1(%) 11.7
ST FTRM2(%) 0.0
LT FTRM2(%) 7.8
VEH SPEED(MPH) 20
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.030
ST FTRM11(%) -94.5
O2S12(V) 0.445
O2S21(V) 0.040
ST FTRM21(%) -93.8
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 4 TM: 10.1
MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 1227
CALC LOAD(%) 16.5
MAF(LB/M) 1.14
MAP("HG) 7.4
COOLANT(°F) 190
IAT(°F) 91
IGN ADV(°) 28.0
ST FTRM1(%) 14.8
LT FTRM1(%) 12.5
ST FTRM2(%) 15.6
LT FTRM2(%) 13.3
VEH SPEED(MPH) 7
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.075
ST FTRM11(%) -85.2
O2S12(V) 0.440
O2S21(V) 0.770
ST FTRM21(%) -0.8
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 5 TM: 13.0
MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 1041
CALC LOAD(%) 12.6
MAF(LB/M) 0.69
MAP("HG) 13.3
COOLANT(°F) 190
IAT(°F) 93
IGN ADV(°) 1.5
ST FTRM1(%) 7.8
LT FTRM1(%) 13.3
ST FTRM2(%) 7.8
LT FTRM2(%) 8.6
VEH SPEED(MPH) 7
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.735
ST FTRM11(%) 26.6
O2S12(V) 0.440
O2S21(V) 0.015
ST FTRM21(%) 37.5
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 6 TM: 15.4
MIL STATUS On
ABSLT TPS(%) 68.6
ENG SPEED(RPM) 3382
CALC LOAD(%) 85.1
MAF(LB/M) 20.54
MAP("HG) 24.2
COOLANT(°F) 192
IAT(°F) 91
IGN ADV(°) 41.5
ST FTRM1(%) 1.6
LT FTRM1(%) 9.4
ST FTRM2(%) 7.8
LT FTRM2(%) 9.4
VEH SPEED(MPH) 20
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.770
ST FTRM11(%) -75.8
O2S12(V) 0.445
O2S21(V) 0.030
ST FTRM21(%) -95.3
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
---------------------
FRAME: 7 TM: 18.3
MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 3072
CALC LOAD(%) 7.1
MAF(LB/M) 1.38
MAP("HG) 4.4
COOLANT(°F) 192
IAT(°F) 91
IGN ADV(°) 45.0
ST FTRM1(%) 0.0
LT FTRM1(%) 11.7
ST FTRM2(%) 0.0
LT FTRM2(%) 7.8
VEH SPEED(MPH) 13
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.040
ST FTRM11(%) -94.5
O2S12(V) 0.440
O2S21(V) 0.020
ST FTRM21(%) -96.1
O2S22(V) 0.445
PTO STATUS Dise
OBD2 STAT CA
=====================
View Freeze Data
P0174 (MOD $10)
TROUB CODE P0174
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 633
CALC LOAD(%) 10.6
MAF(LB/M) 0.45
MAP("HG) 10.6
COOLANT(°F) 199
IAT(°F) 127
IGN ADV(°) 8.5
ST FTRM1(%) 35.2
LT FTRM1(%) 25.0
ST FTRM2(%) 35.2
LT FTRM2(%) 25.0
VEH SPEED(MPH) 1
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
=====================
O2 Monitor Tests
Not Supported by Vehicle
=====================
Diag Monitor Tests
Vehicle did not return data for any
Diagnostic Monitor Tests.
=====================
Vehicle Information
VIN
#1 MOD $10: 3D7KU28C44G271481
CVN
Vehicle is not responding to CVN
requests
CAL ID
#1 MOD $10: 20325253AO
=====================
Modules Present
Module $10: VPW
 
#17 ·
It's running lean. I'm assuming some of that posted above is WOT, hard load? And none of the o2 values go above 440 mv. They should be over 800 mv at WOT.

You probably have a fuel issue, not enough pressure or flow.

Could also be where your MAF is associated to other intake parts, like an elbow. Just had a guy with pinging issues and he narrowed it down to a 90* right by his MAF. MAF needs a few inches of straight in front of and behind.


What are these? Which are bank 1 and which are bank 2? Position 1? position 2? It almost looks like one sensor is in the 2nd position and one sensor is in the first position? Both should be in the first position, since the second position should be deleted.

O2S11(V) 0.155
O2S12(V) 0.440
O2S21(V) 0.080
O2S22(V) 0.445
 
#18 · (Edited)
Yes, the frames around 85% calc load are close to WOT.

O2s11 is upstream bank one. O2s21 is downstream bank two. Right? Supposedly the downstream sensors are disabled in the tune but I see what you are saying that s1b2 looks disabled instead of s2b1. Correct me if I am mistaken.

The problem has remained with two different fuel pumps and two different filters. A walbro 255 produces ample flow. The lines are clear and there is good pressure at the rail. I am running 3 Wabro pickups in the tank. Teed into 3/8" line. The system has been cleaned with seafoam and is full of 89 octane.
 
#21 ·
I don't write the rules. Engines need fuel, air and spark to run. I don't care if you put 16 fuel pumps in a rig that has low flow it's still bad. And do yourself a favor, ditch the Walboro pickups. I can't tell you how many racers I've talked to with issues. We had issues Vegas to Reno with ours as well. Not saying that's your issue right now.....

I want WOT, not close. WOT the MAF numbers will be above 30, which is also a huge load and lots of fuel. 5 is not a high number, or a high load.

You can't disable o2's in the tune. All you can do in the tune is disable CHECKING for them. So if they aren't there, the PCM doesn't care, and never runs the test to look for them. If they are still there, they will read properly - as long as they are functioning properly of course.
Should be this:
O2S11 = Bank 1 Sensor 1
O2S12 = Bank 1 Sensor 2 (downstream)
O2S21 = Bank 2 Sensor 1
O2S22 = Bank 2 Sensor 2 (downstream)

I'll record mine tonight to see what it does with each location.
Thanks Pearce. So the o2s are the correct ones in the correct locations. I checked that a while ago and my memory was hazy.
O2S11 = Bank 1 Sensor 1
O2S11(V) 0.155
O2S12 = Bank 1 Sensor 2 (downstream)
O2S12(V) 0.440
O2S21 = Bank 2 Sensor 1
O2S21(V) 0.080
O2S22 = Bank 2 Sensor 2 (downstream)
O2S22(V) 0.445


According to the info he just posted, your o2's are plugged into the wrong location on the harness. You want your two o2's plugged into bank 1/2, position 1 (upstream). You have them in the downstream location. Downstream doesn't control fuel trims, it only checks catalyst. .1 mv is lean. There is your problem, I bet.

Have you pulled your plugs and verified they are reading lean?
 
#19 ·
Should be this:
O2S11 = Bank 1 Sensor 1
O2S12 = Bank 1 Sensor 2 (downstream)
O2S21 = Bank 2 Sensor 1
O2S22 = Bank 2 Sensor 2 (downstream)

I'll record mine tonight to see what it does with each location.
 
#22 ·
Here's the diagram
 

Attachments

#25 ·
This began happening shortly after I had the PCM reprogrammed from an express van MAF to a truck MAF. The tuner insists it is programmed for the correct mass air sensor. I am also running a brand new Delphi MAF after trying two used ones.
Obviously if it was working perfectly fine before the MAF and tune change then you need to look into the tune, MAF or intake tubing.

You changed something. Sometimes its that simple. Swap the org. tune and parts back and see if it goes away. Be very easy to do.
 
#28 ·
It seems that way. Unless the changes somehow uncovered an issue that was previously within operating parameters and not causing the issue. However that seems less likely than the problem resulting from what changed.

The intake does have a 90 in it. Based on wayne's comments I suppose that could contribute. Besides that the only change was the tune.
 
#27 ·
The rig saw WOT during the testing but the scanner only logs a few moments of data. I think the videos will show it better than the data log.

The highest MAF numbers achieved during testing were 30 or slightly below. Look at data from frame #1 where the MAF was at 18. That was during acceleration slightly before (maybe 2-3 seconds) power cut out.
 
#30 ·
have you considered deleting the MAF and having the tuner reflash and see what happens? that may help you pinpoint the issue if it is in fact with the MAF. i run a 5.3 with no MAF and it runs great-no problems-no complaints-ever. there are many people who would agree and disagree with this but for what im using the rig for it friggin works so im not going to change it.

hope your get it figured out
 
#34 ·
For some reason they starve the motor of fuel. That's what took us out of Vegas to Reno. Well, almost anyway. They were about to, so Josh took his hand and stuck it into the hot fuel tank and got the shit burned out of his arm. He disabled them on the advice from a friend that had the same exact issue at Baja a few months before. After that happened we hauled ass and made it to the next pit just a few minutes before it closed. We made it to the next pit in record time. The next pit, mile ~200, we had all kinds of fuel trim issues and limped in 4lo. No more screen in the tank and it started sucking up foam. Plugged up everything. We were done at taht point.

Now that we aren't relying on those fawking Walboro pick ups, we have a different setup that hasn't caused us any grief since. Granted, we only raced UT since....
 
#36 ·
Here are the videos. We had the gopro clamped to the passenger grab bar and the scan tool taped to the dash. Unfortunately there is some pretty bad glare off the screen of the scan tool.

Despite that I think they still help show what is going on.

Screen 1 is meant to show maf, rpm, tps, etc. Screen 2 is the o2 sensor voltages. Screen 3 is fuel trims. The data log is probably better for seeing what is happening, but you can see how easy the issue is to reproduce accelerating in 3rd gear low range.

The last video is fairly hard acceleration in 4th gear low range. The np435 is being shifted manually of course.

Cam's 6.0L Cutout Troubleshooting, Screen 1 of 3 - YouTube
Cam's 6.0L Cutout Troubleshooting, Screen 2 of 3 - YouTube
Cams 6.0L Cutout Troubleshooting, Screen 3 of 3 - YouTube
GOPR0655 - YouTube
 
#37 ·
I'm the idiot Wayne said burnt his arm......

After watching the videos and looking at the logs, I can't see where you ever reach WOT. The highest TPS % I see is in the 60s. Can you get 100% by pushing the pedal?

The other thing is the fuel trim is way off at idle. Are you sure you are getting fuel? What happend to us was the walbros spun 180 degrees and were pointed up. Then either got pulled or pushed shut by the foam.
 
#38 · (Edited)
I'm the idiot Wayne said burnt his arm......
BTDT, long story but I also burned my arm in a fuel cell years ago so I feel your pain.

After watching the videos and looking at the logs, I can't see where you ever reach WOT. The highest TPS % I see is in the 60s. Can you get 100% by pushing the pedal?
Correct. The refresh rate on the scanner is a little slow but the problem occurred before WOT in those videos. It usually does unless I am in neutral or 2wd or the tires break loose first (in all those cases there is less load on the motor). With the ignition on and the gas pedal floored the TPS reading is 100%.

The other thing is the fuel trim is way off at idle. Are you sure you are getting fuel? What happend to us was the walbros spun 180 degrees and were pointed up. Then either got pulled or pushed shut by the foam.
Based on our pressure gauge testing I am pretty confident I am getting fuel. Still it is worth checking visually. I have not opened up the cell to confirm but I can do that tomorrow evening.
 
#40 · (Edited)
I haven't. I ran speed density for a while. It ran good aside from a lack of low end power. After a couple years like that, the PCM then got a true tune for the first time and it ran great with the temporary van MAF.

The only change made from then to now was switching from the van MAF to the truck MAF and having the pcm reprogrammed for it. I also added a vss, which as you can see in the data log is working properly. It is also calibrated within a couple percent as verified by two GPS receivers.
 
#41 ·
If the only difference is the MAF and the tune, why not switch back to the van MAF and tune? Its a blue green express van PCM right? If it ran great with the van MAF then why change it......

It running so lean is still another issue. Have you shot the exhaust manifolds yet with a thermal gun? Maybe you have an injector issue you don't know. Shoot each exhaust port and see what its doing. Since its lean all the time you'll see it at idle if there is something going on.
 
#42 ·
I can't see it from here. Something is causing your rig to run lean. Figure that out, and your issue will go away. Everything I suggest you say you've already done.

I highly doubt it's a MAF issue. You said unplugging the MAF kept the same fuel trims. If the MAF was the issue, the trims most likely would have changed.

EDIT:
What happens if you unplug the o2's?
 
#43 ·
As I have said before something changed. The MAF and tune. So start there.

Seems to me like its the MAF trims. If they were not changed then it would be physically getting more air at WOT or close to it. And would be getting and be lean because the PCM thinks its still getting a smaller amount of air via the old smaller MAF.

I would double check with your tuner. And make sure the MAF and larger intake tube is tuned correctly.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top