Slight "run on" after shutdown, Any thoughts? |
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Slight "run on" after shutdown, Any thoughts? |
oakdalecurtis |
Dec 7 2016, 12:21 AM
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#1
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Oakdalecurtis Group: Members Posts: 1,336 Joined: 5-June 15 From: Oakdale, Ca Member No.: 18,802 Region Association: Central California |
'76 California 2.0 F.I. stock, 119,000 miles, passes smog every 2 years. Using 89 octane gas and Brad Penn 20/50 oil. Engine starts and runs well, but lately the engine has been "rough running" on for one or two seconds after ignition shutdown. Any thoughts on what might be causing this and what I might do to fix it?
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Dave_Darling |
Dec 7 2016, 01:26 PM
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#2
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914 Idiot Group: Members Posts: 15,048 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
If everything is working correctly, both the spark and the fuel should be instantly cut off when you turn the key off. An engine can continue to run ("diesel") if there are hot spots in the combustion chamber and the fuel keeps coming in, as it would on a carbureted car. But an injected car should also be switching off the fuel when the key goes to off.
Either there is fuel loaded up in the intake somewhere, and you have a hot spot as above, or there is something funky in the ignition circuit. There may be something back-feeding the switched power circuit, for example. Anecdote: I replaced a burned-out bulb in my taillamp cluster with the wrong type; I believe I put a single-filament bulb in a dual-filament socket. The car would not shut off if the turn signal was on, because that activated the "parking light" feature, which tried to illuminate one filament of the dual-filament bulb, which fed back through the bulb socket into the switched-power circuit, and provided power to the ignition and the injection. It is possible that you have something feeding back into the circuit like that. --DD |
pbanders |
Dec 7 2016, 08:14 PM
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#3
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Senior Member Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
If everything is working correctly, both the spark and the fuel should be instantly cut off when you turn the key off. An engine can continue to run ("diesel") if there are hot spots in the combustion chamber and the fuel keeps coming in, as it would on a carbureted car. But an injected car should also be switching off the fuel when the key goes to off. Either there is fuel loaded up in the intake somewhere, and you have a hot spot as above, or there is something funky in the ignition circuit. There may be something back-feeding the switched power circuit, for example. Anecdote: I replaced a burned-out bulb in my taillamp cluster with the wrong type; I believe I put a single-filament bulb in a dual-filament socket. The car would not shut off if the turn signal was on, because that activated the "parking light" feature, which tried to illuminate one filament of the dual-filament bulb, which fed back through the bulb socket into the switched-power circuit, and provided power to the ignition and the injection. It is possible that you have something feeding back into the circuit like that. --DD Wow, impressive diagnosis! I'm certain I don't have any hot spots, quite the opposite, I think I was too lean for a while, just richened my mixture slightly. I never had this problem before going to the Crane, so it makes sense. My guess is that it has a decent-sized capacitor on it's supply line to filter it, and that it takes a couple seconds to discharge after key off. Since you're at idle, mixture is fairly rich, so there's enough fuel in the intakes to supply a couple extra combustions. That's my theory, and I'm sticking to it. Until experiment destroys it (IMG:style_emoticons/default/smile.gif). |
pbanders |
Apr 27 2022, 05:52 PM
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#4
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Senior Member Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
If everything is working correctly, both the spark and the fuel should be instantly cut off when you turn the key off. An engine can continue to run ("diesel") if there are hot spots in the combustion chamber and the fuel keeps coming in, as it would on a carbureted car. But an injected car should also be switching off the fuel when the key goes to off. Either there is fuel loaded up in the intake somewhere, and you have a hot spot as above, or there is something funky in the ignition circuit. There may be something back-feeding the switched power circuit, for example. Anecdote: I replaced a burned-out bulb in my taillamp cluster with the wrong type; I believe I put a single-filament bulb in a dual-filament socket. The car would not shut off if the turn signal was on, because that activated the "parking light" feature, which tried to illuminate one filament of the dual-filament bulb, which fed back through the bulb socket into the switched-power circuit, and provided power to the ignition and the injection. It is possible that you have something feeding back into the circuit like that. --DD Wow, impressive diagnosis! I'm certain I don't have any hot spots, quite the opposite, I think I was too lean for a while, just richened my mixture slightly. I never had this problem before going to the Crane, so it makes sense. My guess is that it has a decent-sized capacitor on it's supply line to filter it, and that it takes a couple seconds to discharge after key off. Since you're at idle, mixture is fairly rich, so there's enough fuel in the intakes to supply a couple extra combustions. That's my theory, and I'm sticking to it. Until experiment destroys it (IMG:style_emoticons/default/smile.gif). Revisiting some of my old posts and updating them... So, I had an issue with my distributor (will make a separate post on this) and ended up swapping distributors and going back to points from my Crane XR3000 system (which had been replaced after failing, but that's another story). And guess what? No more run-on/dieseling after the ignition is switched off. So, yes, it was the Crane that caused the problem. |
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