1995 Mustang GT- No PCM Communication, Runs Rich, Lacks power

[gtrob]

I've got a 1995 Mustang GT(5.0) that's giving me trouble. The car starts, but it's running rich, feels down on power, and the check engine light on. Tried pulling codes with both a scanner and the paper clip method under the hood. No communication. Checked all fuses. Replace the CCRM, no change. Vehicle still runs, but won't communicate at all. At this point, I am not sure if I'm chasing a bad PCM or a wiring issue. Has anyone run into this before, or have advised on where I should start testing next?

 

[General karthief]

Are you plugging in the reader under the hood? The under dash plug on 94-5 GTs don't work,
Most times when the ECU no talkie then it should be sent off to the ECUExchange, that's the go-to place for puter work.

 

[gtrob]

Yes, I am plugging the reader under the hood. Can’t communicate

 

[General karthief]

Did you press one for English???
Yeah, need that ECM looked at..

 

[gtrob]

Is there any way I can check ECM for internal fault?

 

[Noobz347]

Is there any way I can check ECM for internal fault?

Wait... are you Vulcan by chance?

You can try this:

Here’s how you can check for codes if your scanner won’t communicate:

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How to Pull Codes on a 1995 Mustang GT Without a Scanner​

1. Locate the test connectors
   • Open the hood. On the driver’s side near the firewall (by the brake booster), you’ll see a small gray plastic connector (that’s the Self-Test Input, STI) and a black rectangular connector (that’s the Self-Test Output, STO).
   • The gray STI connector usually has a single wire with a white/red stripe coming off the main harness.
2. Get a jumper wire or paperclip
   • You’ll use this to connect the STI to the signal return (SIG RTN) pin on the larger black connector (it’s typically the single black wire with a white stripe, sometimes on a short pigtail next to the main connector).
   • Important: Do not accidentally jumper to the single dark brown wire with orange stripe nearby — that’s 12V for the underhood light and will fry the computer.
3. Turn the key to RUN (don’t start the car)
   • The Check Engine Light (CEL) on the dash will begin to flash. This is called the KOEO (Key On Engine Off) test.
   • Watch the flashes closely. They come in groups separated by a pause. For example: flash-flash (pause) flash-flash-flash = code 23.
4. Read the codes
   • Code 11 (flash–pause–flash) means the computer itself passed its self-check.
   • Other codes will follow in two-digit or three-digit format depending on your ECU (’95s are three-digit).
   • The codes will repeat twice. Write them all down.
5. Run the KOER (Key On Engine Running) test
   • Turn the car off, keep the jumper connected.
   • Start the engine, let it idle.
   • The CEL will flash once, then a pause, then once again (that’s code 111 = system OK).
   • Any other codes will then flash. Record them.

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If No Communication or No Codes​

• If you don’t even get a code 111 with the key on, the ground circuit may be open. The white/lt-blue wire at the STI is tied into the computer’s signal return, and if that ground is bad you’ll get no codes and the car may run poorly (weird idle, fueling issues).
• Check the small black/white ground wire coming off the battery negative cable — it bolts to the body near the starter solenoid. Clean and reattach it if it looks corroded.
• Also inspect the 10-pin connectors (“salt & pepper shakers”) at the back of the intake for corrosion or broken pins. A bad connection here can kill communication.
• If the wiring checks out and you still get no response, the PCM itself may have failed (common on SN95s when the internal capacitors leak).