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engine stumbles when pressing on accelerator

Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 2:25am

Just an fyi I put Dielectric Grease on all Spark plug wires and on all wires connectors I could find under the hood.
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Re: engine stumbles when pressing on accelerator

Postby chem_man » Sep 16 2020, 7:42am

OK on the Carquest spark plug wires. They are a quality wire set. Also, good on putting the dielectric compound on the spark plug wires, and electrical connections.

To address MotorEng91, I am in agreement that the IAT sensor is reading temperature, but my concern is that it is not responding quickly enough relative to the data the Engine Coolant Temperature (ECT) sensor is sending to the PCM. Hence, the PCM could (emphasis on could) be seeing conflicting data while in open loop fuel status at ambient air temperatures below something like 80 Deg F. Also, I did take into account that the data was presented in Deg C. I am able to work with both Deg F and Deg C without difficulty.

NOTE: I am not a professional automotive technician, just a very experienced DIY-er with a great deal of experience in electronics. I've seen thermisters go flaky in non-automotive situations and they can be a bitch to track down especially if they work right above a certain temperature and intermittently below a certain temperature.

robertbassin5, if you have a friend with a 1999 - 2009 Silverado with either the 4.3 V6, 4.8 V8, or 5.3 V8, see if they will let you swap MAF sensors with them for a day or two to either confirm that the IAT sensor is bad, or confirm that it is working properly. That way you don't have to spend any money to test your MAF sensor.
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 2:00pm

These readings are after just starting the truck this mornig

Numbers of DTCs 0
Fuel system 1 statusOL
Fuel system 2 statusOL
Calculated Load Value(%)3.9
Engine Coolant Temperature(°C)39
Short Term Fuel Trim -Bank 1(%)3.9
Long Term Fuel Trim - Bank 1(%)3.1
Short Term Fuel Trim -Bank 2(%)3.1
Long Term Fuel Trim - Bank 2(%)2.3
Intake Manifold Absolute Pressure(kPa)35.0
Engine RPM(rpm) 768
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(°)19.5
Intake Air Temperature(°C)30
Air Flow Rate from Mass Air Flow Sensor(g/s)7.17
Absolute Throttle Position(%)0.4
Location of Oxygen SensorsB1S12--B2S12--
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.870
SHRTFTB1S1(%)3.9
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.625
SHRTFTB1S2(%)N/A
Oxygen Sensor Output Voltage Bank 2-Sensor 1(V)0.815
SHRTFTB2S1(%)2.3
Oxygen Sensor Output Voltage Bank 2-Sensor 2(V)0.500
SHRTFTB2S2(%)99.2
OBD requirements to which vehicle is designedOBDII
Power Take Off(PTO) StatusOFF
Last edited by robertbassin5 on Sep 16 2020, 2:15pm, edited 1 time in total.
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 2:09pm

These readings are after running for about 5 to 10 mins. Up to over a 1000 rpms and holding it there.

Numbers of DTCs 0
Fuel system 1 statusOL
Fuel system 2 statusOL
Calculated Load Value(%)6.3
Engine Coolant Temperature(°C)51
Short Term Fuel Trim -Bank 1(%)10.9
Long Term Fuel Trim - Bank 1(%)1.6
Short Term Fuel Trim -Bank 2(%)13.3
Long Term Fuel Trim - Bank 2(%)1.6
Intake Manifold Absolute Pressure(kPa)31.0
Engine RPM(rpm) 1331
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(°)35.0
Intake Air Temperature(°C)30
Air Flow Rate from Mass Air Flow Sensor(g/s)11.2
Absolute Throttle Position(%)3.5
Location of Oxygen SensorsB1S12--B2S12--
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.880
SHRTFTB1S1(%)7.8
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.690
SHRTFTB1S2(%)N/A
Oxygen Sensor Output Voltage Bank 2-Sensor 1(V)0.910
SHRTFTB2S1(%)10.2
Oxygen Sensor Output Voltage Bank 2-Sensor 2(V)0.805
SHRTFTB2S2(%)99.2
OBD requirements to which vehicle is designedOBDII
Power Take Off(PTO) StatusOFF
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 2:16pm

During this time frame I got a pending code P0300
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Re: engine stumbles when pressing on accelerator

Postby chem_man » Sep 16 2020, 3:18pm

OK on the P0300. Is this with or without the new spark plug wires?

I also notice that from just after starting to after running 5 to 10 minutes your engine coolant temp goes from 39 Deg C to 51 Deg C, a change of 12 Deg C, while the intake air temperature stays at 30 Deg C. My intake air temperature starts to go up within a minute or two of the engine starting. I'm still thinking of a lazy IAT sensor at the "lower temps". On my 1999 Buick Century, from a cold start, I'll see a 5 Deg C change over a 5 minute period.
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 3:21pm

New spark plug wires
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robertbassin5
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 3:30pm

Mine is all in one with the maf.
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robertbassin5
Combustion on 2 pistons [L2]
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Posts: 229
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Re: engine stumbles when pressing on accelerator

Postby robertbassin5 [OP] » Sep 16 2020, 3:32pm

Would it be a good idea to buy a used one?
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Re: engine stumbles when pressing on accelerator

Postby MotorEng91 » Sep 16 2020, 4:30pm

hey chem man, I put the temperature conversions for my own benefit, not to suggest you didn't see it or didn't understand. I just think more clearly in degrees F.

About the IAT, I am not convinced the temperature should increase much at all with engine coolant temp. Maybe a little due to ambient heat in the engine bay. But it depends mostly where your airbox is drawing air from. Mine is from inside the passenger side fender.

Take a look at your short term fuel trims, you go from +3% at idle to +13% at 1300rpm. Suggests you are running lean at higher rpm, could be partially clogged injectors
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