Fox Please help: Electrical load creates missfire ?!

M

martroy

Member

Sep 29, 2024

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Canada

Dec 16, 2024

#101

• Dec 16, 2024

• #101

Update:

As requested, I've look at ignition switch un steering and all wires are ok, no burnt.

I've hook scope straight on battery and I do get that noise there too.

I have unpin all unnessary wires from harness and give a try and still noisy on PIP while creating load.

Last thing I'll have to try is bypass pcm relay and jump solenoid to start engine and create a load with something else (spare electrical fan) since blower wont work.

Thanks for sharing me all your ideas since
I have no clue what is causing this....

 

M

martroy

Member

Sep 29, 2024

73

6

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Canada

Dec 18, 2024

#102

• Dec 18, 2024

• #102

CassieL said:

Try this.
Leave the key off. Make sure your in park or neutral.
Find the eec relay and jump it on.
This will power on everything needed to run engine. Jump the starter solenoid to start engine. Does the symptom return?
What i want to see is the system running and not connected to key on power.

Click to expand...

On my EEC relay, it is used by 4 differents pins. Red, Red/Light green, Yellow and Black.

Color seems different from what found here:

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

With a test light key off, only yellow is powered. With key on, Yellow, Red, Red/Light green are powered, witch make sense. I've remove the relay and create a jumper between those 3 pins.

When doing that, if having all accessories powered like if key was there, witch I guess not what you asked me to do.

Now, if I jump only Yellow to Red, PCM is up but no power on TFI and Ignition coil, witch make sense because in diagram, its needed to make them work. Can you help me out?

I've already tried to remove all fuses and issue was still there. Dont you think it's the same test ?


Thanks

 

M

martroy

Member

Sep 29, 2024

73

6

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Canada

Dec 20, 2024

#103

• Dec 20, 2024

• #103

In the quest of running engine with the minimum electrical components, I'm still facing issues.

Based on those diagram (from Mitchel), I've unplugged yellow wire from solenoid. When I try to jump from PCM relay, Yellow, Red and Red/Light green, I've got a spark as soon as I touch Red/Light green, witch is not correct. I'm just not sure if it's not correct because I do have something to fix on my car or misunderstanding in circuits?

 

Attachments

• Wiring Diagram Engine Control.pdf

  2.8 MB · Views: 72
• Wiring Diagram Ignition switch.pdf

  2.7 MB · Views: 72
• Wiring Diagram_Battery.pdf

  2.3 MB · Views: 78

M

martroy

Member

Sep 29, 2024

73

6

18

Canada

Dec 30, 2024

#104

• Dec 30, 2024

• #104

I'm still facing issue to trying to run engine with minimum electrical components.

Yellow wire unplugged from solenoid, Ignition connector unplugged and jumper on PCM relay (Yellow to Red and Red/Light green). When doing that, cluster is still powered witch I guess shouldnt. Does this means I do have a fault in my wiring?

Thank you guys,

 

General karthief

wonder how much it would cost to ship you a pair

5 Year Member

Aug 25, 2016

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polk county florida

Dec 30, 2024

#105

• Dec 30, 2024

• #105

Have you looked to see if, when the issue occurs, if it is dropping a plug, or several plugs or an injector or injectors?

 

Reactions: Mcmahst

M

martroy

Member

Sep 29, 2024

73

6

18

Canada

Jan 3, 2025

#106

• Jan 3, 2025

• #106

General karthief said:

Have you looked to see if, when the issue occurs, if it is dropping a plug, or several plugs or an injector or injectors?

Click to expand...

Since RPM get messed up, its triggering Rev limiter config in Megasquirt configuration. So there is spark and fuel cut for a split second.

Since I have no clue after all test done, I did order a TFI connector just to bypass all TFI wires straight to battery and ECM and that way, I will be able to start engine without any accessories...

Any other ideas are really welcome !


Martin

 

85fiveohman

New Member

Feb 25, 2011

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Apr 29, 2026

#107

• Apr 29, 2026

• #107

Did you ever figure this issue out? I’m having a exact same issue on a 94 GT.