What's your A/F on Overrun?, 'Nother D-Jet A/F Question |
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What's your A/F on Overrun?, 'Nother D-Jet A/F Question |
BeatNavy |
Mar 12 2017, 12:28 PM
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#1
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Certified Professional Scapegoat Group: Members Posts: 2,924 Joined: 26-February 14 From: Easton, MD Member No.: 17,042 Region Association: MidAtlantic Region |
For those with D-Jet, what are you typically seeing for A/F ratio on a medium to hard overrun? Based on what I've read here mine seems too rich - like in 10's and 11's. Once the RPM's drop closer to idle it bounces back up to normal idle A/F ratios. Does A/F on overrun even matter?
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BeatNavy |
Aug 15 2017, 12:17 PM
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#2
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Certified Professional Scapegoat Group: Members Posts: 2,924 Joined: 26-February 14 From: Easton, MD Member No.: 17,042 Region Association: MidAtlantic Region |
My understanding is that the TPS detects an idle situation and then mixture is controlled by ECU idle settings, not by MPS. Some ECU's cut fuel off above certain RPM on idle, although I can't remember which ECU models off hand. But I'm not going lean, I'm going rich. Mark's explanation about less air would make sense. But that would indicate a fairly normal operation, right? I was under the impression that most people see pretty lean conditions on overrun.
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914_teener |
Aug 15 2017, 12:36 PM
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#3
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914 Guru Group: Members Posts: 5,198 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
My understanding is that the TPS detects an idle situation and then mixture is controlled by ECU idle settings, not by MPS. Some ECU's cut fuel off above certain RPM on idle, although I can't remember which ECU models off hand. But I'm not going lean, I'm going rich. Mark's explanation about less air would make sense. But that would indicate a fairly normal operation, right? I was under the impression that most people see pretty lean conditions on overrun. I believe the overun or "with overun cut off circuit" are listed on Brad Anders site in his part description matrix. I think it.s function is three fold. Driveability, emissions, and fuel economy. I know I have it on my car. You can actually feel it when coasting to a stop when the tps hits the cut off. That is.....when it is adjusted right. |
DRPHIL914 |
Aug 15 2017, 01:46 PM
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#4
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
My understanding is that the TPS detects an idle situation and then mixture is controlled by ECU idle settings, not by MPS. Some ECU's cut fuel off above certain RPM on idle, although I can't remember which ECU models off hand. But I'm not going lean, I'm going rich. Mark's explanation about less air would make sense. But that would indicate a fairly normal operation, right? I was under the impression that most people see pretty lean conditions on overrun. I believe the overun or "with overun cut off circuit" are listed on Brad Anders site in his part description matrix. I think it.s function is three fold. Driveability, emissions, and fuel economy. I know I have it on my car. You can actually feel it when coasting to a stop when the tps hits the cut off. That is.....when it is adjusted right. so you are saying the correct setting is for it to "cut out"? which would then cause the AF reading to go up considerably- which is consistent with my previous experience- when idle circuit is set so that the ECU knob will adjust a/f on idle , it is set in correct position, when it is, I will see the A/F reading go full lean, like 22. - how I have it set now it does not do that - but ive never seen mine go rich like a 9 or 10. I would recheck your TPS board at idle and does it effect a/f and idle when adjusting the ECu knob ? |
914_teener |
Aug 15 2017, 01:58 PM
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#5
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914 Guru Group: Members Posts: 5,198 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
My understanding is that the TPS detects an idle situation and then mixture is controlled by ECU idle settings, not by MPS. Some ECU's cut fuel off above certain RPM on idle, although I can't remember which ECU models off hand. But I'm not going lean, I'm going rich. Mark's explanation about less air would make sense. But that would indicate a fairly normal operation, right? I was under the impression that most people see pretty lean conditions on overrun. I believe the overun or "with overun cut off circuit" are listed on Brad Anders site in his part description matrix. I think it.s function is three fold. Driveability, emissions, and fuel economy. I know I have it on my car. You can actually feel it when coasting to a stop when the tps hits the cut off. That is.....when it is adjusted right. so you are saying the correct setting is for it to "cut out"? which would then cause the AF reading to go up considerably- which is consistent with my previous experience- when idle circuit is set so that the ECU knob will adjust a/f on idle , it is set in correct position, when it is, I will see the A/F reading go full lean, like 22. - how I have it set now it does not do that - but ive never seen mine go rich like a 9 or 10. I would recheck your TPS board at idle and does it effect a/f and idle when adjusting the ECu knob ? I am saying that when the engine is under no load....why worry about AF. Because D jet adjusts mixture by vaccum signature from the MPS ....under decelerarion with the throttle plate in the closed position....the requirement of fuel is not meaningful....so why measure it? My answer would be that you are wasting fuel. The ecu adjustment knob is to set the fuel mixture at idle only. Once the throttle plate is moved that no longer controls AF. |
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