Need a little help here..
04-12-2018, 07:22 PM
#1
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Thread Starter
Need a little help here..
How does the MAP and intake temperature sensor work in conjunction with the ECM, do they contribute to adjustments in the ECM prior to reaching a certain temperature? I'm trying to trouble shoot a backfiring issue through the intake after warm-up. The motor runs great then after 10 minutes I get the backfire when rolling on the throttle and something similar to a misfire while on the throttle. A little background, the motor is a 2000 502 Mag MPI, under 300 hours, I just swapped the cool fuel to a Aeromotive A750 with return regulator set at 42 psi with vacuum unhooked. I also replaced the injectors while I doing the plumbing for the rail. This afternoon was my first run with this setup, prior to the fuel swap I would occasionally have the same issue after a long run.
04-13-2018, 06:37 AM
#3
Platinum Member
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iTrader: (6)
have you checked the timing ? plugs, wires, cap and rotor can all cause similar issues.
04-13-2018, 07:25 AM
#4
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How does the MAP and intake temperature sensor work in conjunction with the ECM, do they contribute to adjustments in the ECM prior to reaching a certain temperature? I'm trying to trouble shoot a backfiring issue through the intake after warm-up. The motor runs great then after 10 minutes I get the backfire when rolling on the throttle and something similar to a misfire while on the throttle. A little background, the motor is a 2000 502 Mag MPI, under 300 hours, I just swapped the cool fuel to a Aeromotive A750 with return regulator set at 42 psi with vacuum unhooked. I also replaced the injectors while I doing the plumbing for the rail. This afternoon was my first run with this setup, prior to the fuel swap I would occasionally have the same issue after a long run.
Need to scan for codes
Is it getting a bit to hot?
Distributor cap clean
Knock module/sensor
04-13-2018, 07:35 AM
#5
Registered
Thread Starter
Cap, rotor, plugs and wires are good. Haven’t checked timing or the TPS, but will tonight. I’m suspecting the ECM is pulling fuel once it reaches operating temperature just by the way it runs for the first 5-10 minutes and didn’t know if a bad MAP and/or intake temp sensor would send the motor that direct... any way of checking these with a volt meter? Something else I should add, on a hard pull while trimming up the tach will jump in sync with the tab button...it’s doesnt effect the way the motor runs but I’ve noticed it and wasn’t sure what’s going on there.
04-13-2018, 07:41 AM
#6
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Thread Starter
Last year it would flutter under a long pull intermittently, which is why I did the fuel swap, but no backfire, the backfire is a new issue, It runs between 160-180 so not getting hot. Im going to check the cap again tonight just to be sure. I’m also going to find someone with a scanner because on my way back to the dock I was getting a diagnosis beep from the ECM. I havent checked the knock sensor, I’ll look into that tonight as well.
Last edited by JonnyT; 04-13-2018 at 09:02 AM.
04-13-2018, 10:17 AM
#7
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iTrader: (1)
Here is some theory - and coolant temp resistance values. Not sure if this will help or not - are you familiar with using a DVOM to diagnose automotive applications? If not, I'd suggest that you do not front probe a connector with your DVOM leads - use a T pin and backprobe so that you do not damage the (very) delicate terminals. Ideally, you could hook up a scan tool to understand what the sensors are telling the ECU.
STARTING MODE
When the ignition switch is turned to the crank position, the ECM turns ON the fuel pump relay and the fuel pump builds up pressure. The ECM then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor and determines the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injectors are turned ON and OFF. This is done by pulsing the injectors for very short times.
RUN MODE
When the engine is started and rpm is above 300, the system operates in the run mode. The ECM will calculate the desired air/fuel ratio based on these ECM inputs: rpm, Manifold Absolute Pressure (MAP) sensor, Intake Air Temperature (IAT) sensor and Engine Coolant Temperature (ECT) sensor. Higher engine load (from MAP) and colder engine temperature (from ECT) requires more fuel, or a richer air/fuel ratio.
Scan Tool Normal Specifications (Idle / Warm Engine / Closed Throttle / Neutral)
Coolant Temp. ° F(° C) 150-170° F (66-77° C)
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine coolant is cold, the sensor (thermistor) resistance is high; therefore, the ECM will see high signal voltage.
As the engine coolant warms, the sensor resistance becomes less, and the voltage drops.
ECT Sensor
Temperature - to - Resistance Values (Approximate)
ECT Sensor
Temperature - to - Resistance Values (Approximate)
°F OHMS
40 7500
70 3400
100 1800
160 450
210 185
STARTING MODE
When the ignition switch is turned to the crank position, the ECM turns ON the fuel pump relay and the fuel pump builds up pressure. The ECM then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor and determines the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injectors are turned ON and OFF. This is done by pulsing the injectors for very short times.
RUN MODE
When the engine is started and rpm is above 300, the system operates in the run mode. The ECM will calculate the desired air/fuel ratio based on these ECM inputs: rpm, Manifold Absolute Pressure (MAP) sensor, Intake Air Temperature (IAT) sensor and Engine Coolant Temperature (ECT) sensor. Higher engine load (from MAP) and colder engine temperature (from ECT) requires more fuel, or a richer air/fuel ratio.
Scan Tool Normal Specifications (Idle / Warm Engine / Closed Throttle / Neutral)
Coolant Temp. ° F(° C) 150-170° F (66-77° C)
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine coolant is cold, the sensor (thermistor) resistance is high; therefore, the ECM will see high signal voltage.
As the engine coolant warms, the sensor resistance becomes less, and the voltage drops.
ECT Sensor
Temperature - to - Resistance Values (Approximate)
ECT Sensor
Temperature - to - Resistance Values (Approximate)
°F OHMS
40 7500
70 3400
100 1800
160 450
210 185
04-13-2018, 10:46 AM
#8
Banned
iTrader: (9)
fuel pressure psi is when backfiring is taking place ? Also laymens test is unscrew the gas cap while running to see if problem stays or not. Fuel venting issue if it clears up.
How old is the coil ??? no mention if that is new as well
My big question is ------ so which injectors did you change out to ? and where did you buy them. That would be a concern as well. Are they new or used ? where they tested , and flow tested before you installed them ?
How old is the coil ??? no mention if that is new as well
My big question is ------ so which injectors did you change out to ? and where did you buy them. That would be a concern as well. Are they new or used ? where they tested , and flow tested before you installed them ?
04-13-2018, 10:52 AM
#9
Registered
Thread Starter
Here is some theory - and coolant temp resistance values. Not sure if this will help or not - are you familiar with using a DVOM to diagnose automotive applications? If not, I'd suggest that you do not front probe a connector with your DVOM leads - use a T pin and backprobe so that you do not damage the (very) delicate terminals. Ideally, you could hook up a scan tool to understand what the sensors are telling the ECU.
STARTING MODE
When the ignition switch is turned to the crank position, the ECM turns ON the fuel pump relay and the fuel pump builds up pressure. The ECM then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor and determines the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injectors are turned ON and OFF. This is done by pulsing the injectors for very short times.
RUN MODE
When the engine is started and rpm is above 300, the system operates in the run mode. The ECM will calculate the desired air/fuel ratio based on these ECM inputs: rpm, Manifold Absolute Pressure (MAP) sensor, Intake Air Temperature (IAT) sensor and Engine Coolant Temperature (ECT) sensor. Higher engine load (from MAP) and colder engine temperature (from ECT) requires more fuel, or a richer air/fuel ratio.
Scan Tool Normal Specifications (Idle / Warm Engine / Closed Throttle / Neutral)
Coolant Temp. ° F(° C) 150-170° F (66-77° C)
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine coolant is cold, the sensor (thermistor) resistance is high; therefore, the ECM will see high signal voltage.
As the engine coolant warms, the sensor resistance becomes less, and the voltage drops.
ECT Sensor
Temperature - to - Resistance Values (Approximate)
ECT Sensor
Temperature - to - Resistance Values (Approximate)
°F OHMS
40 7500
70 3400
100 1800
160 450
210 185
STARTING MODE
When the ignition switch is turned to the crank position, the ECM turns ON the fuel pump relay and the fuel pump builds up pressure. The ECM then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor and determines the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injectors are turned ON and OFF. This is done by pulsing the injectors for very short times.
RUN MODE
When the engine is started and rpm is above 300, the system operates in the run mode. The ECM will calculate the desired air/fuel ratio based on these ECM inputs: rpm, Manifold Absolute Pressure (MAP) sensor, Intake Air Temperature (IAT) sensor and Engine Coolant Temperature (ECT) sensor. Higher engine load (from MAP) and colder engine temperature (from ECT) requires more fuel, or a richer air/fuel ratio.
Scan Tool Normal Specifications (Idle / Warm Engine / Closed Throttle / Neutral)
Coolant Temp. ° F(° C) 150-170° F (66-77° C)
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine coolant is cold, the sensor (thermistor) resistance is high; therefore, the ECM will see high signal voltage.
As the engine coolant warms, the sensor resistance becomes less, and the voltage drops.
ECT Sensor
Temperature - to - Resistance Values (Approximate)
ECT Sensor
Temperature - to - Resistance Values (Approximate)
°F OHMS
40 7500
70 3400
100 1800
160 450
210 185
04-13-2018, 10:59 AM
#10
Registered
Thread Starter
fuel pressure psi is when backfiring is taking place ? Also laymens test is unscrew the gas cap while running to see if problem stays or not. Fuel venting issue if it clears up.
How old is the coil ??? no mention if that is new as well
My big question is ------ so which injectors did you change out to ? and where did you buy them. That would be a concern as well. Are they new or used ? where they tested , and flow tested before you installed them ?
How old is the coil ??? no mention if that is new as well
My big question is ------ so which injectors did you change out to ? and where did you buy them. That would be a concern as well. Are they new or used ? where they tested , and flow tested before you installed them ?
