Ok i have a 91 gt. Basic bolt ons, cam, longtubes, 76mm mass air, 70mm throtte body. It runs great other than one problem. After I start it and drive a few miles it will miss like it's flooding, if I floor it, it clears up, but comes right back. Then after a couple minutes of doing this it will clear up and run great no more problems until it sits and cools off then the same thing again. Any ideas or help is appreciated. New plugs, wires, cap, button, coil. New act sensor, ect sensor. New o2 sensors. Only code I get is about act sensor saying it's an open circuit. Thanks for any help.
Engine 91 mustang gt
- Thread starter bman91gt
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Go to the 'surging idle checklist' in the technical/how to forum, I think that will show you how to test the act sensor and what pin on the computer to test and how to do it.
Here is some info on testing act sensor and wire to the computer:
ACT = Air Charge Temperature. It is normally located in #5 intake runner on the driver's side of the car. It has two wires that connect it to the wiring harness. The temp gauge sender is nearby, but only has one wire and it is a push on connector. The ACT provides information to the computer about what temperature the incoming air is and uses that information to adjust ignition timing and air/fuel ratio. Sometimes the ACT may be relocated to the intake filter airbox because the manifold isn't drilled for it.
ACT & ECT test data:
The ACT & ECT have the same thermistor, so the table values are the same
Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts
Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer. Here's the table :
Voltages are measured across the two connector pins of the sensor with the sensor connected. Some safety pins used to probe the connector from the rear will be helpful
50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61 v
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v
Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms
ACT = Air Charge Temperature. It is normally located in #5 intake runner on the driver's side of the car. It has two wires that connect it to the wiring harness. The temp gauge sender is nearby, but only has one wire and it is a push on connector. The ACT provides information to the computer about what temperature the incoming air is and uses that information to adjust ignition timing and air/fuel ratio. Sometimes the ACT may be relocated to the intake filter airbox because the manifold isn't drilled for it.
ACT & ECT test data:
The ACT & ECT have the same thermistor, so the table values are the same
Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts
Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer. Here's the table :
Voltages are measured across the two connector pins of the sensor with the sensor connected. Some safety pins used to probe the connector from the rear will be helpful
50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61 v
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v
Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms
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