Coast Down Procedure - Misfire Factor Corrections
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From: Atl
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Interesting. Wonder what the algorithm is for determining misfires and how flywheel mass plays into that. Down the google rabbit hole I go.
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Joined: Feb 2024
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From: St. Petersburg, FL
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Joined: Feb 2024
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From: St. Petersburg, FL
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also i think the ASM clutch kiss point is partly determined by the missfire (or maybe just rpm variance) just from the the literature constantly stating "smoother gearchanges" with correct missfire calibration, but who knows?
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The "Coast Down Procedure" is:
1. Car needs to be at operating temp.
2. Drive car safely up to 70mph, with the a/c off, in "D"' or manual allowing car to reach 6th gear.
3. Once 70mph is reached, allow car to coast to 30mph, without hitting the brakes or turning the steering wheel more that 10 degrees
4. Repeat 2 & 3
5. Repeat 2 & 3
6. Repeat 2 & 3 (4 times total with no detection equipment)
NOTE 1: If you hit the brakes anywhere during the process, it will abort the sequence. That process won't count and you will need to do it again. With your experience, 4 successful procedures "should" relearn the sequence. You won't know unless AM dealer checks.
NOTE 2: With a battery replacement, you will need to reset radio pre-sets, window dip, and seat memory.
1) Is it 70 > 30, or 70 > 20? Aston1936 claims 20, but that last 10 mph seems to take the longest.
2) Do all 4 runs have to happen in immediate sequence? As in, I need enough room to do all 5 without ever touching the brakes? Or is it just that the brakes can't be touched between each 70-30 run? Since I'm in the middle of a major city, that clarification makes a significant difference in how far I have to drive to get to a place to do this...
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I was trying to figure out how to use my Foxwell OBDII scanner to determine if my car has "learned" from the coast-down procedure, and found this thread that details exactly how to check this parameter and read misfires for each cylinder:
https://www.pistonheads.com/gassing/topic.asp?t=1834621
The Foxwell tool is nice and has a lot of data, but it can be a little hard to traverse. So, this writeup helped to make sense of the PID codes and whatnot.
My outcome was that my car has indeed re-learned it's misfire correction, and that after an hour of driving (granted, with very little idling), my highest misfire count was 3 in cylinder #11 which doesn't give me much pause at all. I do have some 'lumps' in idle on occasion, but they're super super minor and I can't hear any sounds from the exhaust. If not caused by misfire then i'm not really worried about it...the fuel in the car is a little old, and that could cause it too.
https://www.pistonheads.com/gassing/topic.asp?t=1834621
The Foxwell tool is nice and has a lot of data, but it can be a little hard to traverse. So, this writeup helped to make sense of the PID codes and whatnot.
My outcome was that my car has indeed re-learned it's misfire correction, and that after an hour of driving (granted, with very little idling), my highest misfire count was 3 in cylinder #11 which doesn't give me much pause at all. I do have some 'lumps' in idle on occasion, but they're super super minor and I can't hear any sounds from the exhaust. If not caused by misfire then i'm not really worried about it...the fuel in the car is a little old, and that could cause it too.
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Have you tried dumping a can of seafoam in your tank and then taking it for a good run?
I hadn't driven my vantage s in a while (several weeks) and it felt a big sluggish, and having never put any engine treatment in the car in my few years of ownership (and although low miles, I had patchy service history form the prior owner), I decided to give it a try.
I poured in the seafoam on a nearly fully empty tank, then filled up.
When I started the car, it made some stutters (never done that before) then a brief puff of white smoke came out of the exhaust and it's been smooth sailing ever since. Runs like a dream.
I would give it a try, you could have some gummed up piston rings and/or injectors and seafoam might help.
I hadn't driven my vantage s in a while (several weeks) and it felt a big sluggish, and having never put any engine treatment in the car in my few years of ownership (and although low miles, I had patchy service history form the prior owner), I decided to give it a try.
I poured in the seafoam on a nearly fully empty tank, then filled up.
When I started the car, it made some stutters (never done that before) then a brief puff of white smoke came out of the exhaust and it's been smooth sailing ever since. Runs like a dream.
I would give it a try, you could have some gummed up piston rings and/or injectors and seafoam might help.
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