Electrical gurus please help.

[stanley514]

Ok I have replaced all the normal relays EEC,Fuel Pump etc. My 92 Has blown two ECMs. I feel I have a dead short to one of the sensors. Where should I start looking for a short first?
Or where can I find a diagram of what to check first?

If anyone has had a dead short and found it how about telling me where it was.

Thanks

P.S this wiring is all stock no mods.

 

[jrichker]

How did the computer die? Will it still spit out codes?
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.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

Here's a link to get the diagrams you'll need...
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

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

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Start by ohming out the ACT & ECT wiring with the computer and sensors disconnected. You should see 10 meghoms or more.

Check pin 26 (VREF) on the computer wiring harness with the computer disconnected. VREF is supplied to the EGR, MAP and TPS sensors. If you get less than 12 ohms with all of them connected, disconnect them one at a time and watch the change. The one that causes the resistance to increase beyond 10 ohms when it is disconnected is suspect.

 

[stanley514]

Thank you jrichker. I will let everyone know what I find.
Stanley514

 

[stanley514]

I have a OTC 4000E made by MAC. Can't get any codes from the ECM at this time.
Stanley514

 

[stanley514]

Ok per jrichker. Less than 12ohms with EGR, MAP and TPS connected or disconnected.

My Diagnostic schematic says I have service short to ground replace ECM? I've already done this and blown a 2nd ECM??

 

[stanley514]

Ok the fuel pump won't stop. It is making pressure. I have replaced the relay. I installed a new pump trying to fix this problem. The old pump was a Walbro 155lph
I installed a Walbro 255lph. The plug ins were the same I just plug up the new pump. Could this wire be grounding the wrong side?? The car has run with this pump but it is blowing ECM's ?
I haven't found any shorts yet?

 

[jrichker]

Ok per jrichker. Less than 12ohms with EGR, MAP and TPS connected or disconnected.

My Diagnostic schematic says I have service short to ground replace ECM? I've already done this and blown a 2nd ECM??

Following the ECC diagram, 88-91 eec pinout.jif, with the computer disconnected and the sensors disconnected, pins 26(VREF), 47 (TPS), 27 (EGR), and 45 (MAP) should be an open circut and measure greater than 10 Megohms. Pin 46 (Sig Return) is a ground, but with the computer disconnected, should also be an open circuit.

 

[stanley514]

Well its running. I bought a Breakout box. I checked everything with it. I didn't find any shorts. So I installed a Good used computer. The car started the first try. I have drove in about 120+ miles no problems yet.
I installed 2 rebuild P.O.S. computers from Advance. The car with both boxes failed. I made no changes just the used computer and it lives. With the Advance computers both of them the engine wouldn't rev past 1/3 throttle. The engine would die then blow black smoke then shut off. When this happen 4/5 times the engine wouldn't start anymore. Then the fuel pump would keep running no 3 sec prime. I was getting fire just no fire to the injectors.
Well fix now. Thanks Guys