MAF swap issue

[krkline2gdsm]

I have an 87 mustang. I did a MAF swap. I bought a new main harness and a new ECU. The harness (part number M-12071-C302) is for a MAF car and the ECU is for a MAF car. I am getting no power to the fuel pump. The old relay to the fuel pump was under the driver seat but the new harness relocates this relay under the hood on the passenger side. I tested this relay connection point and found there only to be on 12v signal out of 4 wires. There should be 2 12v signals when the car is on. If I understand correctly, 1 wire is 12v hot all the time, 1 wire get the 12v signal to click relay over to then send the 12v hot wire to another wire that powers the pump and the last 4th wire is the ground.

After looking at schematics, I tested the ECU for power. The yellow wire gets power. All the rest of the wires get nothing. I looked at an ECU pinout and tested the pins that were supposed to get a 12v signal and nothing. Just the one 12v wire going into the ECU. The ecu is hanging loose and I hooked up one ground wire that was in the harness near the ECU. I tested the TFI module and only 1 of those wires get a 12v signal.

I thought a simple MAF swap was easy but I guess not. Car cranks but no fuel. Just cranks. The ground strap from head to firewall gets really hot after 5 seconds of cranking to the point it smokes. I checked all fusable links in the front at soleniod and all are good.

I dont know anymore... I am thinking its a grounding issue with this ECU. Tried plugging in the old ECU and still no power to pump. Has to be in the main harness as far as grounding... has to be.

ideaS?

 

[krkline2gdsm]

also to add, i have checked the ground in harness under ecu (body ground), sanded, retapped for new bolt and tested ground. I also did the same for the EEC ground.

 

[jrichker]

You would have been much better off simply buying the one of the MAF conversion harness kits. They run from $16-$35 and are easier to install than a new computer wiring harness.

Your current problem is because you do not have power to the computer power relay or you have not connected the computer power ground, or both.

The ground under the computer is not the computer power ground!!!! It is the shield ground for the TFI to computer wiring. The computer power ground is a heavy gauge (10 gauge) black/green wire that normally comes out of the wiring harness near the starter solenoid.

The wire colors changed in sometime in late 90 to early 91, so your 87 body wiring colors will not match up to the new harness you have. See http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif for wiring harness with colors that match your 87 Mustang. The diagram says 88-91 Mass Air, but the 87 is the same with the exception of the Mass Air and the Thermactor Air control circuits.

The M-12071-C302 should be similar to the 92-93 5.0 Mustang harness. The color descriptions I will use refer to the 92-93 harness. If yours don't match, the only way I can help you is for you to scan the manual that came with the harness and either post it or email it to me.

Diagram courtesy of Tmoss & Stang&2birds
92-93 5.0 Mustang computer wiring harness

The yellow wire which connects to pin #1 on the computer goes to the fuse link on the yellow wire on the starter solenoid. Be sure that you do not bypass the fuse link by attaching the yellow wire directly to the starter solenoid. On an 87, the same wire will be black/orange. The yellow wire on the new harness will have power at all times. If it does not, then you have mis connected something.

Pins 37 & 57 on the computer will have power with the key in the Run position if the computer power relay has power. If not and the yellow wire has power, then you do not have power at the red/green wire on the computer power relay. If you do have power on the red/green wire with the key in the Run position, then you do not have the coil ground wire for the computer power relay properly connected to ground.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

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

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for94-95 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

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

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[strtrcr50]

That harness technically is not plug and play with a SD car. The only harness that is a direct swap is an 89 harness. I'd suspect you found that it was different where the 2 dash connectors hook up(Near the self test connector) in addition to the fuel pump relay moving under the hood. FRPP should be able to tell you what to repin. Give their tech line a call at 800-367-3788.

 

[krkline2gdsm]

You would have been much better off simply buying the one of the MAF conversion harness kits. They run from $16-$35 and are easier to install than a new computer wiring harness.

Your current problem is because you do not have power to the computer power relay or you have not connected the computer power ground, or both.

The ground under the computer is not the computer power ground!!!! It is the shield ground for the TFI to computer wiring. The computer power ground is a heavy gauge (10 gauge) black/green wire that normally comes out of the wiring harness near the starter solenoid.


The yellow wire which connects to pin #1 on the computer goes to the fuse link on the yellow wire on the starter solenoid. Be sure that you do not bypass the fuse link by attaching the yellow wire directly to the starter solenoid. On an 87, the same wire will be black/orange. The yellow wire on the new harness will have power at all times. If it does not, then you have mis connected something.

Pins 37 & 57 on the computer will have power with the key in the Run position if the computer power relay has power. If not and the yellow wire has power, then you do not have power at the red/green wire on the computer power relay. If you do have power on the red/green wire with the key in the Run position, then you do not have the coil ground wire for the computer power relay properly connected to ground.

Bought a new main harness because the other one was all cracked up and wires were suspect.

The ground you speak of that comes out of the harness near the starter solenoid, that is a good ground. Sanded down to fresh metal, self tapping screw, and bolted it in. Even tested that ground with a multimeter gauge to confirm its a good ground.

The yellow wire at the ecu does get power at all times (pin 1). I tested all fusible links from solenoid and after the link, all get power. According to schematics for an 87, its the black/orange wire w/ fusible link, as you already stated.

No other pins, including pins 37 and 57 get power with key on.

My brother is with the car now but I called him and asked him to check the computer relay. He said there is a yellow wire that runs into the relay and a yellow wire that runs into the ECU, both those wires get power. No other wires on the ECU or the relay get power including the black/red wire you asked about.

So what if the yellow wires to the ECU/relay getspower and the relay doesn't put out the power? BTW: We have tried 2 new relays there also.

 

[krkline2gdsm]

Give their tech line a call at 800-367-3788.

They wont be able to do anything for me.

 

[krkline2gdsm]

Looking at all those schematics, tomorrow I am going to jump the turn on wire to the relay for the ECU and if needed, make a new ground for that relay. If the ignition signal to the relay is suspect, I will follow it back to the fusible link under the dash (that I did not know about ) and replace if needed.

Thanks for the schematics. I am confident enough to say that I dont see this being an issue much longer. Port up results tomorrow