Fox Please help: Electrical load creates missfire ?!

[martroy]

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....

 

[martroy]

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.

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

 

[martroy]

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?

 

[martroy]

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]

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

 

[martroy]

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

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]

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