I'm an idiot

flashback87 · Oct 1, 2011

well, i went to try and pull my codes with the paper clip and test light. I grabbed the first connector i saw, which was the brown one and not the grey sti, and connected that to the cpu connector via the paperclip.

now, no codes will pull. did i fry the cpu? (of course this is the new cpu i got for my maf conversion that was only $30)

thanks,

jrichker · Oct 1, 2011

The computer pin 46 signal ground is a critical component: it provides ground for the
Map/Baro, TPS, ECT, EGR position sensor and ACT. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground,
although both may have a common connection origination point. Signal ground usually
has some conditioning that reduces the electrical noise to prevent false readings
The black/white wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. If this ground is bad, none of the sensors mentioned
will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. What sometimes happens is that the test connector black/white wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.

Troubleshooting signal ground problems:

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. That means disconnecting either the battery positive or negative cable since there is always some current draw due to the computer and radio circuits.

1.) With the power off, measure the resistance between the computer test ground
(black/white wire) on the self test connector and battery ground. You should see less than 2.0 ohms.

2.) MAP circuit: 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 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice
inside the main harness where the wire from the 10 pin connectors joins the rest of the black/white wire. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 2.0 ohms.

3.) Engine mounted sensor circuit: Check the resistance between the black/white wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the black/white wire.
Repeat the process for the ACT and ECT sensors. Your results should have the same specifications.

See the graphic for the location of the 10 pin connectors:

See the graphic for the 10 pin connector circuit layout.

flashback87 · Oct 1, 2011

thanks,

i tested the ground on the diagnostic tester and it was below 2.0 i think. I am not too sure i am measuring the ohms correctly. Can some one help with this? i know i hook the voltmeter up to the ground wired and ground terminal on battery but what seeting do i use on the voltmeter? i have 5 settings, 20m, 200k, 20k, 2000 and 200.

also, i am pretty sure the tps is meesed up now because when i start the car my idle spikes to 2500 rpm's.

so what are my options? do i need a new cpu, or do i need to rewire stuff?

thanks again,

flashback87 · Oct 1, 2011

ok, so i put my meter to the 200 setting on ohm and when i tested the ground wire on the engine diagnostic connector it read 165.

What does this mean? I am just confused what i need to do after i do these tests.

can someone please help? i think i really might have messed things up.

thanks

jrichker · Oct 2, 2011

Figure out how electricity works and how to use your meter BEFORE you do anything else. After you have a basic understanding of how things work, the instructions I posted above will make sense.

Automotive circuits are mostly simple stuff: a power source, a connection path, a control device, a load, and a ground.
The battery/alternator is the positive power source.
The wire and fuses are the connection path.
Control devices are switches, relays and sensors.
A load is a light, motor, solenoid or heater element.
In automotive circuits, grounds are the return path so the electrical power can flow from the load to the negative side of the power source.
Electricity flows like water:
Voltage is like pressure,
Current in amps is like volume,
Resistance is like the kink you put in a garden hose to decrease the pressure or volume.
Power is pressure multiplied by volume or voltage multiplied by current (amps)

Digest that, and you just got the first 3 days of Electricity 101.

Use some jumper wires (connection path and ground) to hook up a switch (control device), a battery (power source), a light bulb (load). Now make the light turn on and off with the switch.

That's the electrical lab for the first week of Electricity 101. People pay hundreds of dollars and sit in hard chairs in a stuffy classroom to learn what I just told you for free. So smile, you just got an expensive lesson for free

For free automotive electrical training, see Automotive Training and Resource Site . I have personally reviewed the material and it is very good.

Step 1.) Find the instruction book that came with your Multimeter. Read it and familiarize yourself with how it works and how use it. If you lost the book or didn’t get one with it, do a Google search on the web to find the manufacturer’s web site & download a copy of the manual.

Step 2. ) Make sure that you know what test lead plugs into which jacks on the Multimeter. There are usually several different jacks on most Multimeters, and they have different functions. Make sure that your battery(s) in the Multimeter are good: if you have any doubts, replace the battery(s).

Step 3.) Once you are sure that the Multimeter is functional and you have the leads plugged into the jacks for Ohms ( the upside down “U” symbol), do some simple measurements to make sure that you know how to use it correctly. Set the switch to the lowest range and touch the leads together: you should not see “nothing” but you should see 1.0-0.3 ohms. Measure a 60 watt light bulb: cold it will measure about 17.5 Ohms. It you measure it while it is hot, the reading will be greater.

Step 4.) Make several test measurements using the ohms function and the DC volts function. Remember all resistance measurements must be done with the power off the circuit. This avoids false readings and possible damage to the ohmmeter.. Repeat steps 3 & 4 until you are sure that you can do it without making any mistakes.

Step 5.) Then see Repair Info | AutoZone.com and carefully study ALL the information under the Heading Chassis Electrical, Basic Electricity – Understanding & Troubleshooting

Step 6.) Go back and carefully re-read both of my previous posts and download and print the diagrams from the following website for some help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Step 7.) Apply what you have learned and make the test measurements using the information in the wiring diagrams & my previous posts. You will find either a broken wire or bad connection in the signal ground circuit .

flashback87 · Oct 2, 2011

jrichker said:
Figure out how electricity works and how to use your meter BEFORE you do anything else. After you have a basic understanding of how things work, the instructions I posted above will make sense.

Automotive circuits are mostly simple stuff: a power source, a connection path, a control device, a load, and a ground.
The battery/alternator is the positive power source.
The wire and fuses are the connection path.
Control devices are switches, relays and sensors.
A load is a light, motor, solenoid or heater element.
In automotive circuits, grounds are the return path so the electrical power can flow from the load to the negative side of the power source.
Electricity flows like water:
Voltage is like pressure,
Current in amps is like volume,
Resistance is like the kink you put in a garden hose to decrease the pressure or volume.
Power is pressure multiplied by volume or voltage multiplied by current (amps)

Digest that, and you just got the first 3 days of Electricity 101.

Use some jumper wires (connection path and ground) to hook up a switch (control device), a battery (power source), a light bulb (load). Now make the light turn on and off with the switch.

That's the electrical lab for the first week of Electricity 101. People pay hundreds of dollars and sit in hard chairs in a stuffy classroom to learn what I just told you for free. So smile, you just got an expensive lesson for free

For free automotive electrical training, see Automotive Training and Resource Site . I have personally reviewed the material and it is very good.

Step 1.) Find the instruction book that came with your Multimeter. Read it and familiarize yourself with how it works and how use it. If you lost the book or didn’t get one with it, do a Google search on the web to find the manufacturer’s web site & download a copy of the manual.

Step 2. ) Make sure that you know what test lead plugs into which jacks on the Multimeter. There are usually several different jacks on most Multimeters, and they have different functions. Make sure that your battery(s) in the Multimeter are good: if you have any doubts, replace the battery(s).

Step 3.) Once you are sure that the Multimeter is functional and you have the leads plugged into the jacks for Ohms ( the upside down “U” symbol), do some simple measurements to make sure that you know how to use it correctly. Set the switch to the lowest range and touch the leads together: you should not see “nothing” but you should see 1.0-0.3 ohms. Measure a 60 watt light bulb: cold it will measure about 17.5 Ohms. It you measure it while it is hot, the reading will be greater.

Step 4.) Make several test measurements using the ohms function and the DC volts function. Remember all resistance measurements must be done with the power off the circuit. This avoids false readings and possible damage to the ohmmeter.. Repeat steps 3 & 4 until you are sure that you can do it without making any mistakes.

Step 5.) Then see Repair Info | AutoZone.com and carefully study ALL the information under the Heading Chassis Electrical, Basic Electricity – Understanding & Troubleshooting

Step 6.) Go back and carefully re-read both of my previous posts and download and print the diagrams from the following website for some help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

Step 7.) Apply what you have learned and make the test measurements using the information in the wiring diagrams & my previous posts. You will find either a broken wire or bad connection in the signal ground circuit .

Thanks a lot. this is really good info and givg me a solid foundation.

flashback87 · Oct 4, 2011

ok, so i did the tests above, and let me explain what i did( and yes i read through all the links jrichker referenced above). i checked resistance between the computer test ground right after the self-test connector and the batter ground pig tail right next to the batter by the windshield washer fill tank. that was .5. I did the same with the tps and bar/map using the battery ground pigtail by windshield washer fill tank and those were both .5.

i took the cpu out and opened it up and saw that one of the traces looked fried. my buddy can do circuit board soldering so he put a wire in to fix the trace.

now when i start my car the idle does not spike anymore but i still can not pull the codes. also, the car smells pretty rich.

do you think i just need a new cpu? can i put the old speed density cpu in and see if that will go into test mode or will that mess things up since i coverted it to maf?

i apologize for the newbie and obvious questions but you guys are helping me learn a ton and i really apreciate it!

jrichker · Oct 4, 2011

The old computer will not work properly since the MAF conversion involves moving several wires around to different pin locations.

Keep in mind that 86-88 cars did not have a working check engine light, so you will need a test light or votlmeter to read the pulses from the computer.

flashback87 · Oct 4, 2011

I am using the paperclip and test light method.

I was thinking about putting the old speed density cpu in to only see if I could pull codes/get cpu in test mode. I figured rhat would tell me if the maf cpu was bad and I should get a new one.

I just wanted to clarify as my post above was not well explaied.

Will that work?

Thanks a lot for helping me with this

jrichker · Oct 5, 2011

You said all of the wiring checked out and that you found a burned trace inside the computer. Going on that, I would replace the computer.

Noobz347 · Oct 5, 2011

Here... Save yourself some headache if you're having difficulty with getting the codes. I bought one of these years ago from Walmart (they don't appear to have them anymore), but Amazon does. No flash counting, no paper clips, no B.S..

I had to install a jumper into the cannon plug going to the pigtail harness on the tranny to run the KOER codes but that was simple.

Amazon.com: Equus 3145 Ford Digital Code Reader: Automotive

flashback87 · Oct 5, 2011

When my buddy repaired the fried trace he said it looked like another trace looked damaged near where the damaged trace connects. I'll see if fixing that makes a difference first.

If I new cpu is needed is a reman unit from an auto parts chain store a decent option?
I got my current one off craigslist for $30 but that seems rare.

Thanks

jrichker · Oct 5, 2011

flashback87 said:
When my buddy repaired the fried trace he said it looked like another trace looked damaged near where the damaged trace connects. I'll see if fixing that makes a difference first.

If I new cpu is needed is a reman unit from an auto parts chain store a decent option?
I got my current one off craigslist for $30 but that seems rare.

Thanks

As long as th part numbers match up and you get a good warranty, the Auto Parts Remain is a good idea,

flashback87 · Oct 6, 2011

so the autozone near by had a maf cpu in stock and they let me go up there and put it in to see if it would fix my problem (pretty sweet of them).

well with the new computer in i tried to start running the codes with a paper clip and the fuel pump did not prime. so, i asked autozone to hook up there code scanner and they did not read anything either.

i thought the cpu would cure this for sure but it did not. I am pretty confused now. i did the resistance tests above and they all seemed to pass. i ever did the bar/map one more time and it was still .5.

i did notice witht he cpu from autozone it was not smelling as rich.

what do you guys think?

please give me some advice.

thanks

jrichker · Oct 6, 2011

The basic check is to measure the resistance between computer pin 46 and pin 60 or pin 37. It should be less than 1 ohm. It it isn't, the computer (even the new one) has problems.

flashback87 · Oct 6, 2011

jrichker said:
The basic check is to measure the resistance between computer pin 46 and pin 60 or pin 37. It should be less than 1 ohm. It it isn't, the computer (even the new one) has problems.

thanks,

i unscrewed the cpu from the connector and placed one probe of my multimeter on pin 60 and the other probe on pin 46 on the cpu. it measured at .5 when set to 200 on the ohm setting. i then reconnected and measured it at the wires for pin 60 and 46 at the connector and that was also .5.

i must be missing something. anymore advice please?

thank you for your patience and helping me

flashback87 · Oct 8, 2011

well, i was finally able to pull my codes so i guess the cpu is good since my friend soldered it.
.
i only did the koeo and got 22. ive been doing some research and i did the volt and resitance tests. both seem good. acutally the volt test was 4.97. is that ok?

if i need a new bar/map are they interchangelable from anyother ford cars?

jrichker · Oct 12, 2011

You probably have already done this testing, but just in case, here it is again...

MAP/BARO sensor operation and code 22

Revised 19-Jul-2011 to add functional descriptions for MAP and BARO operation.

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 acts to sense 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 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.

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

Baro or MAP test using frequency meter - 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.

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.

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