Engine Multiple engine codes

No need to create multiple posts just to get your post count up.

Instead of pestering General karthief, ask me - I am the one who wrote the instructions.

Post #180 has the revised code 26 instructions. The MAF voltages are tested with the engine running.

Judging from your comments, either you didn't bother reading all the instructions or you didn't understand them.

The 12 volts for the MAF heater can only be measured with the ignition switch in the Run position.
Do not use body, engine or chassis ground when making resistance or voltage measurements unless specifically instructed to do so.

MAF output readings: Use the computer connector diagram to help choose the proper pin connection on the computer when measuring the MAF output voltage. . Since the car is most likely parked for simplicity's sake, the idling voltage check can the done with the voltmeter directly stuck in the backside of the MAF connector.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

If the output of the MAF C&D pins exceeds the specs above, there are two possible problems:

1.) The MAF sensor is defective and needs to be replaced.
2.) The MAF sensor is installed in a a different housing than the one it was designed for. The sensor is designed to work with a specific MAF part number or model MAF housing.

Check the resistance of the MAF signal wiring. For the next 2 checks make your measurement with the MAF disconnected from the wiring harness. You are checking the resistance of the wiring between the MAF wiring connector and the computer wiring connector.

Computer wiring harness connector, wire side.


Computer wiring harness connector, computer side.



Pin D on the MAF wiring harness and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF wiring harness and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and pins A or B.

TTSaleen05 said:

i also tested the MAF harness ground wire(pin B) to the negative post of the battery. I got nearly 4 ohms, then I tested that same wire to chassis and got nearly 10 ohms. Any ideas?

Click to expand...

A bad ground will keep the MAF sensor from heating up and not reducing the MAF voltage output. This would cause an overly rich mixture at all RPM ranges.

Voltage drop testing of connections and grounds.

Use a Digital Volt Meter (DVM) to measure the voltage drop across a connection or wire. Adding length to the test leads may be required, and does not affect the accuracy of the test. Use 16-18 gauge wire for the test leads if you have to lengthen them.

Voltage drop increases with the increase of current in a circuit and it also increases with heat. Put a maximum current load on a bad wire or connection and it gets hot and drops more voltage across the wire or connection. As it heats up, resistance increases which makes more heat. Round and round you go in a vicious circle until something catches fire or fails.

Voltage drop testing must be done while the usual load is on the circuit. If it is a starter, it has to be tested while cranking the starter. If it is lights, A/C or fan, they must be turned on high while testing. Fail to do this and you will not get accurate results

1.) Most grounds use the negative battery post as their starting point. Keep this in mind when checking grounds.
2.) The voltage will be small if the ground is good: less voltage drop = better connection.
3.) Be sure that the power to the circuit is on, and the circuit is being used in its normal manner. For instance, if it is a light circuit, the lights on that circuit should be powered on.
4.) To measure grounds, place one DVM lead on the battery negative post and the other on the wire or connector that goes to ground.
5.) 5.) Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections (sensors are low voltage devices and small drops can have a large effect on the devices dependent on sensor accuracy)
0.0V Connections
A voltage drop lower that spec is always acceptable.
6.)
See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .

TTSaleen05 said:

thanks jrichker, if the MAF ground is compromise. Is it probable that the other sensors that share that ground is compromised as well? And when testing the voltage drop, you said it should be in use. So that means I have to probe the negative wire of the sensor with a safety pin?

Click to expand...

That is correct.

TTSaleen05 said:

thanks jrichker, if the MAF ground is compromise. Is it probable that the other sensors that share that ground is compromised as well? And when testing the voltage drop, you said it should be in use. So that means I have to probe the negative wire of the sensor with a safety pin?

Click to expand...

The MAF uses the same ground as the computer.
The following are diagrams courtesy of Tmoss & Stang&2birds

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


Engine mounted fuel injector harness


5.0 wiring diagram for Fuel Injectors, Sensors, and Actuators


Grounds

This checklist applies to all Mustangs , not just the EFI equipped cars. Some of the wiring will be different on carb cars and carb conversions

Revised 26 –Oct -2016 to add fuel pump ground to the list.

Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

Make sure that all the ground places are clean and shiny bare metal: no paint, no corrosion.

1.) The main power ground is from engine block down by the oil filter to battery: it is the power ground for the starter & alternator.


2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery, computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972


Correct negative battery ground cable.


3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

All the grounds listed in items 1,2 & 3 need to bolt to clean, shiny bare metal. A wire brush or some fine sandpaper is the best thing to use to clean the ground connections.


4.) All the sensors have a common separate signal ground. This includes the TPS, ACT, EGR, BAP, & VSS sensors. This ground is inside the computer and connects pin 46 to pins 40 & 60, which are the main computer grounds. If this internal computer ground gets damaged, you won't be able to dump codes and the car will have idle/stall/ performance problems

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) Fuel pump ground the fuel pump has a ground pigtail the connects to the body under the gas tank. You have to drop the gas tank to see where it bolts to the body.



See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections
0.0V bolt together connections



]

Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.[/b]