Can't pull codes.

[strtrcr50]

I just swapped my 88 speed density computer and harness for an 89 mass air computer and harness. Everything is in and it runs fine, but I can't pull any codes with my code reader. On my 89 harness, there are 4 wires from the diagnostic connector, and the one in the corner by itself was cut. On the speed density harness that came out, there was only 3 wires. What do I hook the 4th wire to?
Thanks in advance
Rob

 

[85ragtop]

I could be wrong about this, but if I remember right the one by itself plugs into the main harness. Right beside the three prong.

 

[strtrcr50]

Sorry. I'm not really explaining myself correctly. There is the one wire connector, and there is the diagnostic connector. On my mass air harness, one of the wires that goes to the diagnostic connector was cut. It is the one that is not there in a speed density connector. Now the code reader will only read 000 and not go into test mode. I'm assuming that is because of the cut wire.

 

[85ragtop]

I see. Yea that could be why. Sorry it has been a long time since I messed with an EFI car.

 

[strtrcr50]

From looking at wiring diagrams, it looks like that is a fuel pump test wire? JRichker, can you help?

 

[jrichker]

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See http://www.troublecodes.net/Ford/

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

 

[strtrcr50]

I've been trying to dump the codes with a eqqous scanner. It worked fine until I changed the 88 speed density setup to an 89 mass air setup. Now the scanner just stays at 000 and will not go into the test mode. Is this caused by the fuel pump?(the wire that is in a 89 harness that is not in an 88 harness) being cut?

 

[jrichker]

I've been trying to dump the codes with a eqqous scanner. It worked fine until I changed the 88 speed density setup to an 89 mass air setup. Now the scanner just stays at 000 and will not go into the test mode. Is this caused by the fuel pump?(the wire that is in a 89 harness that is not in an 88 harness) being cut?

Nothing in the fuel pump circuit should keep you from dumping the codes.

Computer will not go into diagnostic mode on 86-90 model 5.0 Mustangs

How it is supposed to work:
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. Since it is a dedicated ground, it passes through the computer on its
way to the computer main power ground that terminates at the battery pigtail ground. It should
read less than 1.5 ohms when measured from anyplace on the engine harness with the battery
pigtail ground as the other reference point for the ohmmeter probe.

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. Only an experienced electronics technician can open
the computer up & repair the trace if it burns up and creates an open circuit.

The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering
it to power can produce unknown results, including damage to the computer. The ohm test
simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
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
1.5 ohms.

If that check fails, remove the passenger side kick panel and disconnect the computer
connector. There is a 10 MM bolt that holds it in place. Measure the resistance between
the black/white wire and pin 46 on the computer wiring connector: it should be less than
1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms or less, then the
computer is suspect. On the computer, measure the resistance between pin 46 and pins
40 & 60: it should be less than 1.5 ohms. More that that and the computer’s internal
ground has failed, and the computer needs to be replaced.

If the first ground check was good, there are other wires to check. Measure the
resistance between the STI computer self test connector (red/white wire) and pin 48 on
the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem

The following is a view from the computer side of the computer connector.

Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the black/white wire goes. Almost every
sensor on the engine except the MAF is connected to it.

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

 

[Red88 RICK]

i have a question slightly related to this and dont wanna start a new thread so here it is. i also have an 88 SD which i converted over to MAF and i also put in a bulb for the check engine light a while back not knowing that the 88's didnt have a working light but anyways the light will turn on only when im turning the key shouldnt it go on as a regular check engine light like i have a feeling i have a few codeds stored in there i havnt had the time to get the paperclip out and look but im running rich as paris hilton ha and when i do the paperclip do i need a test light now shouldnt the engine light blink also?

Edit: also where did you get that scanner from iv been looking around at speedshops and liek little parts stores around here but nothing only that stupid one that flashes at me for $30 iv seen seom online for $30 with a screen but i dotn wanna buy offline ha (i hate waiting) but i will if thats the only choice anyone buy theres at a store?

 

[strtrcr50]

I got my scanner from amazon.com. I'll try checking the wiring as listed.
Thanks,
Rob

 

[jrichker]

[

i have a question slightly related to this and dont wanna start a new thread so here it is. i
also have an 88 SD which i converted over to MAF and i also put in a bulb for the check
engine light a while back not knowing that the 88's didnt have a working light but
anyways the light will turn on only when im turning the key shouldnt it go on as a regular
check engine light like i have a feeling i have a few codeds stored in there i havnt had the
time to get the paperclip out and look but im running rich as paris hilton ha and when i do
the paperclip do i need a test l ight now shouldnt the engine light blink also?

Edit: also where did you get that scanner from iv been looking around at speedshops
and liek little parts stores around here but nothing only that stupid one that flashes at me
for $30 iv seen seom online for $30 with a screen but i dotn wanna buy offline ha (i hate waiting)
but i will if thats the only choice anyone buy theres at a store?

If you follow the instructions below, you will not need an extra test lamp. They detail making the
check engine light work on an 86-88 Mass Air conversion car.
Copied from mustang88GT:

"I have not finished it yet but I put the bulb in and it works. There are wires that you can tap into
and run to the self test connector. The reason I have not run the wires yet is because I am
tripping 2 codes because I did not run wires for the secondary fuel pump or speed senor yet
for the MAF conversion... but it should be real easy to do here is

Adding a "Check Engine" light
Another difference between the speed density and MAF cars is that MAF cars have a "Check Engine"
light in the dash to alert you to possible serious problems and it makes reading out self test
codes much easier. The MAF cars have the "Check Engine" light located in the light panel on
the lower right of the instrument cluster. Speed density cars don't have this window, but there is
a "Check Engine" position for a light in the tachometer face, though there is no bulb installed.
The wire from the EEC to the bulb (via the flex connector) is also missing.
In the '88 harness (not sure of other years), there is a tan and a black/blue wire connecting up
to the 'Check Engine' circuit on the instrument cluster flex circuit. For MAF models, the tan wire hooks
to the EEC STO/MIL line and the black/blue is for the lamp test out when you start the car. I don't
know what these are connected to in an '88, but the test out feature does not work, and the STO/MIL
line at the EEC-IV and self test connector is yellow/black. The wires connected to the check engine
lamp probably end at some open connector somewhere, but I couldn't track it down, so I cut
the tan and black/blue wires off the flex connector and ran a new wire to the STO/MIL wire on the
self test connector under the hood (you could also tap in by the EEC-IV, but it was easier for me to go
through the firewall. You can get a bulb socket from the HELP! rack at the local parts store, put in a
N194 bulb, and voila, you now have a working check engine light."

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx –
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

I have heard some rumors of WalMart having them, but I can't confirm that.