Anyone have an A3M schematic?

[kingmeirl]

My computer and some wires got wet due to rain water getting inside. I pulled the computer apart and found 2 capacitors bad. One of them pulled right off and I am not sure which way the new one goes on (i believe they are polarized). So.... does anyone have an internal schematic of the A3M?

Thanks

 

[jrichker]

A9L, yes, A3M no. And yes, the caps are polarized. Look closey at the PCB and you may find a + on one of the solder pads where the cap mounts.

 

[kingmeirl]

Nothing on the board. I am 95% sure of the orientation of the one I pulled off. From what I have been reading, a solid line on the side of the capacitor indicates negative. The new ones are marked and the positive lead is longer. I got the new ones soldered in and the comp back in the car before dinner. Still no start. I check the tps and I have 1V supply but I have to manually spin the inside all the way 'open' to get a max reading of .7V. So obviously the comp isn't supplying enough voltage to the tps. I have 12V supply to the IAC.
I'll continue the search. Maybe salt/pepper shakers. What pin in the comp supplies voltage to the tps?
Oh, and thank you for the quick reply!!!!!

 

[C6AE]

I don't have a schematic, but I'm pretty sure I've got an A3M kicking around somewhere if you need one...

 

[jrichker]

Pin 26 orange/white wire on the computer is 5 volt VREF used for TPS, BARO & EGR sensors. Make sure you have +5 Vref at the BARO, TPS & EGR sensors. Check the BARO sensor mounted on the firewall behind the upper intake for +5 Vref first. It is good there and not at the TPS & EGR, check the salt & pepper 10 pin connectors.

Diagram courtesy of Tmoss & Stang&2birds

91-93 5.0 Mustang computer wiring

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 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

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

 

[kingmeirl]

Pin 26 was brown with a white stripe. Only .5V coming out of the comp. I did find 5V at pin 22, so I jumped pin 22 to the vref wire at the salt/pepper connector. I cut the vref wire so voltage wouldn't go back to the comp. After doing that, I got good 5v to the tps, so I set the tps to .98. The car still wouldn't start. I caved and sent the comp off to autozone to be rebuilt for $80. Should be back in three days.

 

[jrichker]

Pin 26 was brown with a white stripe. Only .5V coming out of the comp. I did find 5V at pin 22, so I jumped pin 22 to the vref wire at the salt/pepper connector. I cut the vref wire so voltage wouldn't go back to the comp. After doing that, I got good 5v to the tps, so I set the tps to .98. The car still wouldn't start. I caved and sent the comp off to autozone to be rebuilt for $80. Should be back in three days.

Pin 22 is the test wire for the fuel pump. It gets grounded by the computer to turn the fuel pump relay on. I highly recommend you spend some time studying the EEC wiring diagrams at wiring Mustang FAQ - Wiring & Engine Info

 

[kingmeirl]

I jumped off pin 22 to send 5v to the tps hoping the computer would be able to read the voltage coming off the tps so it would fire the investors. It didn't work.
I got a rebuilt comp from autozone today ($68 since I had $20 on my rewards card) and she fired right up! Now I have to find where that water got in. Thanks for all your help, saved me lots of time and money.