Thinking bad EEC. Can someone confirm?

You cannot measure resistance on a circuit that is powered up. You will measure the small voltage drop in the circuit due to the current flowing through it. That will upset the meter's reading. You must have no power on the circuit to get an accurate reading. Disconnect one of the battery terminals prior to making any resistance measurements on the EEC circuitry.

The orange/white wire is supposed to be 5 volts for the sensors. Pin 46 is the signal ground for the same sensors. No 5 volts, the sensors don't work. No signal ground, the sensors don't work.

The break in theharness is probably at the junction where 37 & 57 are soldered to the fuse link. The fuse link is back by the starter solenoid, and is a blue wire that comes off the starter solenoid.

Make your test measurements at the computer wiring connector to eliminate the wiring harness as being the source of the problem.

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error. Warm the engine up until you get good hot air from the heater and then dump the codes again.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

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.

Voltages may be measured across the ECT/ACT by probing the connector from the rear. A pair of safety pins may be helpful in doing this. Use care in doing it so that you don't damage the wiring or connector.

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

Diagram courtesy of Tmoss & Stang&2birds



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

jrichker said:

The Mass Air computers from 89-93 are interchangeable with a few exceptions. Just be
sure you use the MAF & MAF sensor from the same series computer. The auto transmission
computers use a different start circuit than the manual computers. You can use an auto
trans computer in a 5 speed car with no problems or changes. I have done it in my original 89 Mustang GT, and I know it works OK. I have no positive input or comments on using a 5 speed computer in an auto trans car. I personally would not do it.

The odd duck is the 93 Cobra computer, labled X3Z which is interally calibrated for 24 lb injectors. Try and avoid it if you can.

All the following are mass air unless they say Speed Density

8LD - MANUAL 88 5.0L Mustang Speed Density
8LF - Auto 88 5.0L Mustang Speed Density
A9L - 89-93 5.0L Mustang 5-spd
A3M - 93 5.0L Mustang 5-spd
A3M1 - 93 5.0L Mustang 5-spd
X3Z - 93 5.0L Cobra 5-spd
A9P - 89-93 5.0L Mustang Auto
A9S - 88-93 5.0L Mustang California
C3W - 89-93 5.0L Mustang Auto
DA1 - 87 5.0L Mustang 5-spd Speed Density
J4J1 - 94-95 5.0L SVT Cobra 5-spd
T4M0 - 94-95 5.0L GT Vert 5-spd
U4P0 - 94-95 5.0L GT Auto
W4H0 - 94-95 5.0L GT
ZA0 - 95 Cobra R
D9S - Lincoln LSC
ZXA3
LLX3
CCA1
CCA0
AOL2
AOL3

Click to expand...

So I have a DA1 but my car has had the mass air wired into the harness just before the EEC plug...what I'm gathering out of this post is that my car won't run right( cuz it current isn't running right) with a mass air sensor wired into the harness?...ive bees having trouble following somebody else's chop up job...i found it with the red hot wire spliced into pin 37 And just left the other side of the 37 there hooked to nothing..so I wired 57 And 37 along with the red wire from the mass sensor...and I had a bad ground somewhere(I grounded 40 pin to the frame)...and it started but runs like complete ...so I'm hoping if I got the a9l that it would iron this out

Purdytang9 said:

So I have a DA1 but my car has had the mass air wired into the harness just before the EEC plug...what I'm gathering out of this post is that my car won't run right( cuz it current isn't running right) with a mass air sensor wired into the harness?...ive bees having trouble following somebody else's chop up job...i found it with the red hot wire spliced into pin 37 And just left the other side of the 37 there hooked to nothing..so I wired 57 And 37 along with the red wire from the mass sensor...and I had a bad ground somewhere(I grounded 40 pin to the frame)...and it started but runs like complete ****...so I'm hoping if I got the a9l that it would iron this out

Click to expand...

[v]You did 2 things wrong:[/b]
1.) You piggybacked on someone else's post. - bad manner, bad idea. Start your own post.
2.) Right now there is no info about your car's model year, EFI or carb, no mods listed. Makes it hard to troubleshoot when we don't know what you have.


DAI is a Speed Density computer. It does not use a MAF and cannot be modified to use a MAF.

When you start your own post, I will be glad to help you.
Joe R.