1992 LX 5.0 mystery. use to run now doesn't. HELP

@voodoo18

I have personally seen occasions when the engine would not start until a plug wire was disconnected and then try to start to it. I don't have a solid answer for that,

I do have a few suspicions; spray the inside and outside of the distributor cap and rotor with WD40, wait 5 minutes and them wipe them dry. I suspect that the coil spark is bypassing the rotor and finding another path to ground. The extra gap provided by the insertion of the spark tester reduces the voltage so that it does not jump to ground and goes where it is supposed to go.

voodoo18 said:

the daalbert@yahoo.com is the right one

Click to expand...

Hi, Sent.
-John

Post the vid on YouTube and link it here.

Olivethefet said:

Post the vid on YouTube and link it here.

Click to expand...

If you’re asking it that’s correct, yes, that’s how to list your video here.
-John

voodoo18 said:

Just took a code reading. 22 and 24. 22 is Manifold absolute pressure (MAP) or BARO sensor out of range. 24 can either be Intake air charge temp sensor or vane air temp sensor out of range. OR coil #1 primary circuit failure. You think I should put my original coil back on? and what does MAP have anything to do with not getting spark?

Click to expand...

MAP/BARO sensor operation and code 22

Revised 24 Oct 2018 add warning about trying to measure the MAP/BARO sensor output with a common multimeter.

On a Speed Density car, the MAP/BARO sensor is connected to the intake manifold and acts to sense the manifold pressure. Lower vacuum inside the intake manifold when combined with more throttle opening measured by the TPS means more airflow through the engine. As airflow increases, fuel flow through the injectors needs to increase to keep the air/fuel ratio where it needs to be. When manifold vacuum increases, the engine is either decelerating or idling, and it needs to reduce the fuel flow through the injectors.

On a Mass Air car, the MAP/BARO sensor vents to open air and actually senses the barometric pressure due to changes in weather and altitude. Its purpose is to set a baseline for the computer to know the barometric pressure. As barometric pressure decreases, it leans out the fuel flow to compensate for less oxygen in the air. When the barometric pressure rises, it increases to add fuel since there is more oxygen in the air. The fuel requirements decrease as altitude increases, since the atmospheric pressure decreases.

Disconnecting the wiring connector from the MAP or BARO sensor will set code 22..

Misconnecting the BARO sensor to vacuum on a Mass Air car will cause the computer to lean out the fuel mixture.

Code 22 or 126 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There a very few DVM’s with a price tag under $40 that will measure frequency, but there are some out there.

Map sensor wiring:
black/white - ground
orange/white or +5 volts power
white/red signal out.

Measure the +5 volt supply using the orange/white and black/white wires
Measure the signal using the black/white and white/red wires.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold on 86-93 Mustangs.

The Baro or MAP sensor can only be tested using a real frequency meter. The sensor output is a square wave which cannot be accurately measured with a common multimeter. Run the test key on, engine off.. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout. And oscilloscope is very useful if you have access to one or know of someone who does. With an oscilloscope, you can see the waveform and amplitude.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.






Diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

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HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

87-92 power window wiring

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:



Code 24 - Intake Air Temperature (ACT) sensor out of range.
Bad sensor, bad wiring. The ACT for Mustangs built before 95 is in the
#5 intake runner. It measures the air temperature in the intake to help
computer the proper air/fuel ratio.

Note that that if the outside air temp is below 50 degrees F that the test for the ACT can be in error. Warm the engine up to operating temperature and retest.

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 :

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
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