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I agree with Peter. Check cold compression dry and wet. Also make sure your timing marks are right on. I had a similar condition and found the intake cam was off it's mark by a few degrees. Adjusted the valves and timed it right, really made a difference. Follow up with warm compression test.

Then put a DVM on the O2 sensor, one lead to the signal wire (on the spade connector, but don't disconnect this wire from the car), the other lead to ground. Run the leads into the cabin of the car and have someone monitor the DVM as you run the car through its warmup etc. This should confirm or rule out the lean condition.
 

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Discussion Starter #22
02 Sensor Voltage Data!

I just hooked up a DVM to the 02 Sensor.

Engine Cold, Ignition on: about .54v
Cold Idle: About .54-.60v
Acceleration (no load), about .70-.84
Acceleration (load), about .77-.90v (AFM flapper spring is about 5-7 clicks looser than stock).

HERE'S THE MAIN ISSUE:
When the condition occurs (push the pedal down while under load until "hesitation range" is hit - part throttle or full throttle makes no difference - have already checked TPS), the 02 voltage drops to about .22v!!!! (I ran long leads from the sensor so that the DVM could ride shotgun).

I also noted that the Alfa-spec voltmeter in the instrument panel drops by about one volt when the condition occurs. I have yet to contemplate the possible meaning of that data.

Keep the ideas coming, and thanks again!
 

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Well, well, well. Our '86 Graduate with the resistive wiring can be made to do the same thing (re: stumbling and voltage drop) by turning on too many accessories drawing switched power. The AC fan (interior and on the condensor) can drag the voltmeter down by a couple of volts, the formerly frozen ventilation fan could be counted on for a bit more, and when the indicator dropped below about 9-10 volts, the engine would start to stumble. I'd suggest you have a wiring fault (maybe some broken strands) between your ignition key and the ECU power. It is probably drooping spontaneously below the voltage required for proper ignition, or perhaps even running the fuel pump. Try hot-wiring the ECU power, if you feel like it, and see what happens.
 

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MrT is correct that the L-Jet ECU will not run at less that 10.5v.

Check the wiring, fuses and relays under the parcel shelf. Put your DVM on the cigarette lighter and see what the voltage is when this occurs.

-Peter
 

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Curious as to what was the cause in the end?

I'm experiencing random only when warm stumble at above 3000. Drives along all day, then start to stumble badly and unable to go above 3000. It progresses to poor driving at any rpm, and will then only run with a heavy throttle application. Problem is it goes away when it cools down. Yesterday it start fine, as usual, I drove a half mile in 75 degree weather and it started to happen. I park her a few hour and in 72 degree weather ran as if there was no issue. Happily pulling to redline.
Hoping the answer here will get me started. I suspect my old ignition wires, as most of the sensors have been replaced in the past two years.
 
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