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1986 base model Astro 4.3
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Discussion Starter · #21 ·
After isolating the wire from the ESC to the ECM, hooked up my meter at the ECM end and it showed a steady 9.4 volts. Now I'm wondering if I tried to rev it while I was doing that test. I will repeat this test just to be sure. I have also run separate wire, sensor to ESC, ESC to ECM, ESC ground directly to negative on battery all with the same results.
 

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I'm running out of ideas. What happens when you disconnect the tan wire and rev it? Have you looked at the spray pattern when you rev it?

One thought I had was maybe the pressure regulator is going bad and when you rev it the fuel pressure goes out of wack, the sensor detects a knock and it retards the timing.

I'd also check fuel pressure, it could be the pump itself is weak so it idles ok but can't keep up with acceleration.
 

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1986 base model Astro 4.3
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Discussion Starter · #23 ·
Thanks for following Bikley, when I disconnect the "tan wire", first the idle drops because there is not advance. When I then rev, it falls on it's face which I think is to be expected because there is no advance, timing stays at TDC when disconnected. I will post a video of the spray pattern under load. I have plenty of fuel, almost twice the minimal needed, new fuel pump, new fuel pressure regulator, new injectors. The spray looks good under any condition but from my limited experience, this is the only one I have ever seen and I have not found a worthy video for comparison.
 

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Discussion Starter · #25 ·
I will try that and I'm guessing that would work in the short-term thanks. My goal is to eventually get through emissions and re-register as a "classic" which here in Arizona is a yearly nominal fee with no more smog check. Then I can really try some hot-rodding tweaks but for now, I need to figure out more than just a Band-Aid on a cancer. I DID meter the voltage again ESC to ECM with revving and no change, steady 9.4 volts. Thanks again, in no way do I want to diminish your effort to get me on the road, appreciate it.
 

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My thought on advancing the timing was to eliminate a fuel issue if it ran smooth, but the fact that you don't have a change in voltage when you rev it, it tells me that either the knock sensor or more likely the ESC module is faulty. I realize that you replaced them but new doesn't always equal good.
 

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Ok I'm stumped. I've combed every GM forum I could find and about the only things I can come up with are:
Bad ESC or knock sensor.
Bad ECM.
Bad ignition module.
Bad distributor
Engine knock
Bad O2 sensor
Bad coolant temp sensor
Bad TPS sensor
Bad EGR
Incorrect or faulty fuel injectors
Incorrect diagnosis

I've learned a lot researching this but I'm no closer to finding a solution than on day one.
 

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1986 base model Astro 4.3
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Discussion Starter · #28 ·
Thanks Bikley for all your effort and research, I will direct my first attention to determining if the ESC module was perhaps bad out of the box, then work my way down the list which looks like you put in order of likelyhood and or importance. All those items are "new" BUT I know it isn't unheard of a replacement part not working from the get-go. I'm out of town but will follow up with a post upon completion. I will also try your advance advice just to have all the boxes checked. I too am "stumped", thanks.
 
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