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Old 06-20-2012, 11:40 PM   #1
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Default no engine braking?

What settings do I play with if the revs are not dropping when I left of the gas and I'm still in gear? E.g., I'm driving at 40 mph in 4th, I see a red light so I go off the throttle but the car just continues on at 40 mph or maybe VERY slowly starts to slow down. It's clear that the car is not engine braking like I'm accustomed to.

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Old 06-20-2012, 11:47 PM   #2
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Sounds like overrun fuel cut?

Does it idle high? If you rev the engine without load, does it linger at higher rpm abnormally long?
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Old 06-20-2012, 11:50 PM   #3
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?

Regardless of over-run, a closed throttle will cause engine braking.

Are you sure that the throttle is not physically binding up? Eg, if you were to drop it into neutral and release the throttle, what would the engine do?
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Old 06-21-2012, 12:22 AM   #4
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I will try neutral tomorrow and see. I did confirm that the TPS was at zero during this (also tried recalibrating TPS). I'll try to get it in a log.
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Old 06-21-2012, 12:42 AM   #5
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A revision to my last:

Regardless of over-run, a closed throttle will cause engine braking, presuming that the IAC valve isn't stuck wide-open (and even then, it's kind of a stretch.)
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Old 06-21-2012, 12:46 AM   #6
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in addition to cutting fuel, you need to cut air, so either one the other or both are not being cut

so like joe said, in addition to checking fuel overrun cut Id look at the iacv
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Old 06-21-2012, 03:34 AM   #7
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At what RPM is that?
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Old 06-21-2012, 08:39 AM   #8
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I want to say it's around 3000. I am about to drive to work. I'll update in abit.
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Old 06-21-2012, 08:44 AM   #9
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Take a datalog if possible, remember to hit spacebar at the exact moment you notice the problem.
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Old 06-21-2012, 08:49 AM   #10
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Will do
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Old 06-21-2012, 09:46 AM   #11
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My money is on the IAC valve. Occasionally my PID stuff whacks-out and decides to idle at the cut-off limit of 3000rpm for a few seconds or longer, then reconsiders and lowers RPM.

Dimitris,
I still owe you some data, maybe tomorrow before the gastro-enterologist.
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Old 06-21-2012, 09:57 AM   #12
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I think the log is too big to attach? The upload keeps failing? Is there a way to chop the log into smaller pieces? For now, screen shots are attached.

The first two markers (earlier on in the log) kind of bracket one of the examples. Looking at the first one, the rpms went from 2563 to about 1500 over 15 seconds. That's a drop of 66 rpms/sec for those keeping score at home. The third marker identified the end of one of the examples. That time the rpms went from 2912 to 2324 over about 10 seconds. That's a drop of 58 rpms/sec. Am I being too critical?

The last marker identifies where the car almost stalled out after coming to a stop with the AC on.
Attached Thumbnails
no engine braking?-example-1.jpg   no engine braking?-example-2.jpg   no engine braking?-ac-example.jpg  
Attached Files
File Type: msq 6-21-12am.msq (89.3 KB, 81 views)
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Old 06-21-2012, 10:40 AM   #13
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I have a feeling your idle settings are fubar. Is your iacvv staying open?
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Old 06-21-2012, 10:42 AM   #14
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How do I determine if it is?
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Old 06-21-2012, 10:43 AM   #15
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Look at the log.
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Old 06-21-2012, 10:50 AM   #16
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I can't find where that is indicated... Do I have to add that parameter to the log? Or is just not called iacvv? I've got a lot to learn...
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Old 06-21-2012, 11:03 AM   #17
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Idle steps or something like that....been a while since I looked at an ms1 log
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Old 06-21-2012, 11:10 AM   #18
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Maybe I'm confused, but this is one of Rev's units that is based on MS2 right?

There is a "PWM Idle Duty" that was holding steady at 25.8 during the first example. For the second example, that value was at 40.2 for the first 5 seconds and dropped to 25.4 for the last five seconds.
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Old 06-21-2012, 11:11 AM   #19
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Maybe I should have pointed out that my car is a normally aspirated '99.
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Old 06-21-2012, 12:02 PM   #20
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Allen send the datalog to my email please.
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