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Discussion Starter #1
So I'm stumped for once...

I'm having an ignition issue on my 90 GT. It will run great...for weeks even. Then it will start losing tach and spark. I thought it was a wire break, but yesterday I pulled the harness and tested the ignition wiring for breaks, from before Y junction to ECU plugs. All wiring I tested was good.

I plug everything back in. Car won't start. I jostle and hold up the ECU harness and it starts just fine. I set wiring down, lose spark/tach and dies.

I've resoldered the pads for the input legs on the ECU, thinking that the solder joints were cracked...but that has not fixed the issue.

what am I missing here? When plugged in, the ECU harness connectors have quite a bit of movement, also they seemed fairly sturdy when I had everything apart.


There's a 90 GT in the junkyard I'm going to go see if the ECU is still there...hopefully it is.

2,321 Posts
If it starts and runs it doesn't seem to be an internal ecu issue.
90% of your description point's to a ground issue, most of the cars grounding points are small white plastic plugs with multiple black wires that bolt to the frame with an m6 bolt and nut.
The ground harness connection that causes the symptoms you describe is next to the battery bolted to the "inner fender", undo the retaining nut or bolt and make sure all the female ground fittings are on the male ground bar and there is no corrosion.
Also the ground point on the transmission that has two black wires going to one metal ring held in place by a short m6 bolt (10mm) any ground loss there would also cause the same symptoms.

reconnecting the ecu could reset it and allow it to work for a while with an unsteady ground signals or the prongs in the harness plug to the ecu aren't connecting, the 90+ has tiny pins at the ecu and both sides of the female connector in the plugs that goes over the ecu pins sit close together, looks for gaps in the harness plug females.
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