IS THIS NORMAL? (Gauge Cluster Question)
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
It is not normal for our cars to do this--it could be the battery being weak, or a blown fuse--specifically fuse 2.21 (5A) in the Central Junction Box, under the dash. That fuse supplies continuous power to the PCM to maintain the KAM (Keep Alive Memory).
If your gauges are sweeping when you turn the key on then the PCM is not retaining the various things it learns (long term fuel and idle air trims, etc.) and is starting out from "scratch" each time your start the car. The gauges sweep purposely as an alert that the PCM memory has been lost.
There are performance and fuel economy issues related to this--if the long term fuel trims never get optimised it affects WOT and near WOT performance...
If your gauges are sweeping when you turn the key on then the PCM is not retaining the various things it learns (long term fuel and idle air trims, etc.) and is starting out from "scratch" each time your start the car. The gauges sweep purposely as an alert that the PCM memory has been lost.
There are performance and fuel economy issues related to this--if the long term fuel trims never get optimised it affects WOT and near WOT performance...
4th Gear Member
Joined: May 2008
Posts: 1,842
From: Santa Monica, CA
Well here is something I've always wanted to know:
Ever since I changed my battery to an Odyssey PC680MJT, I've noticed that it does this SOMETIMES. I've checked the fuses, they are all still good. I know I PM'ed you about this before Cliffyk and you said that my small battery may cause the cluster or something to dip below a certain voltage at start-up, causing the sweeps.
I have worked on my car many times where I had to disconnect the battery for over 5 minutes, which resets the KAM. The thing is, I can notice a difference between when I've disconnected the battery and when my PCM is supposedly reset due to the voltage dipping low at startup/getting sweeping gauges.
Whenever I reset the KAM by having the batt disconnected, I can gently rev up the car and it would hang at around 1100-1200rpm's for a few seconds before going down.
When my gauges sweep occasionally as I said eariler, it doesn't do this.
So is my KAM still being reset if I am seeing sweeping gauges?
Ever since I changed my battery to an Odyssey PC680MJT, I've noticed that it does this SOMETIMES. I've checked the fuses, they are all still good. I know I PM'ed you about this before Cliffyk and you said that my small battery may cause the cluster or something to dip below a certain voltage at start-up, causing the sweeps.
I have worked on my car many times where I had to disconnect the battery for over 5 minutes, which resets the KAM. The thing is, I can notice a difference between when I've disconnected the battery and when my PCM is supposedly reset due to the voltage dipping low at startup/getting sweeping gauges.
Whenever I reset the KAM by having the batt disconnected, I can gently rev up the car and it would hang at around 1100-1200rpm's for a few seconds before going down.
When my gauges sweep occasionally as I said eariler, it doesn't do this.
So is my KAM still being reset if I am seeing sweeping gauges?
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
Well here is something I've always wanted to know:
Ever since I changed my battery to an Odyssey PC680MJT, I've noticed that it does this SOMETIMES. I've checked the fuses, they are all still good. I know I PM'ed you about this before Cliffyk and you said that my small battery may cause the cluster or something to dip below a certain voltage at start-up, causing the sweeps.
I have worked on my car many times where I had to disconnect the battery for over 5 minutes, which resets the KAM. The thing is, I can notice a difference between when I've disconnected the battery and when my PCM is supposedly reset due to the voltage dipping low at startup/getting sweeping gauges.
Whenever I reset the KAM by having the batt disconnected, I can gently rev up the car and it would hang at around 1100-1200rpm's for a few seconds before going down.
When my gauges sweep occasionally as I said eariler, it doesn't do this.
So is my KAM still being reset if I am seeing sweeping gauges?
Ever since I changed my battery to an Odyssey PC680MJT, I've noticed that it does this SOMETIMES. I've checked the fuses, they are all still good. I know I PM'ed you about this before Cliffyk and you said that my small battery may cause the cluster or something to dip below a certain voltage at start-up, causing the sweeps.
I have worked on my car many times where I had to disconnect the battery for over 5 minutes, which resets the KAM. The thing is, I can notice a difference between when I've disconnected the battery and when my PCM is supposedly reset due to the voltage dipping low at startup/getting sweeping gauges.
Whenever I reset the KAM by having the batt disconnected, I can gently rev up the car and it would hang at around 1100-1200rpm's for a few seconds before going down.
When my gauges sweep occasionally as I said eariler, it doesn't do this.
So is my KAM still being reset if I am seeing sweeping gauges?
Then there is that nasty trait we humans all share, placebo effect and its kin. We often "notice" a difference when we expect to notice one, and very whether there is a real difference or not. The opposite holds as well, we often do not notice a real change if we were not expecting change.
As an example, installing a louder intake or exhaust system on a car will make 99.44% of people notice, and believe, that the engine has become more powerful--even when in some instances the opposite is true. This is what sells CAIs, "off-road" mid pipes, and fart-cannon exhaust tips (these mostly on the ricer side of town). It's why "butt-dyno" reports are all to be taken with a grain of salt.
Getting back to the KAM, the difference between how the engine runs immediately after clearing the KAM, and once the adaptive learning has done its thing, is related closely to how well the tune has been setup. If the MAF curve and injector slopes are dead-on then short term fuel trims will be hovering around 0.0% and the long term trims (averages of the STFTs) will be at or very near 0.0%--essentially there's nothing to learn.
If however the STFTs are way out either rich or lean then the LTFTs (used in open loop mode)--learned as averages of the STFTs--will also be whacked-out and will be what is applied in open loop.
Generally this is bad and very often is why people with poorly tuned, cobbled together from "pieces/parts", setups see the AFR bouncing all over and difficult to control at WOT.
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
4th Gear Member
Joined: May 2008
Posts: 1,842
From: Santa Monica, CA
Yes, if the gauges sweep then the KAM has been reset, or was very very close to having been reset as a result of a voltage drop in the PCM's continuous power feed.
Then there is that nasty trait we humans all share, placebo effect and its kin. We often "notice" a difference when we expect to notice one, and very whether there is a real difference or not. The opposite holds as well, we often do not notice a real change if we were not expecting change.
As an example, installing a louder intake or exhaust system on a car will make 99.44% of people notice, and believe, that the engine has become more powerful--even when in some instances the opposite is true. This is what sells CAIs, "off-road" mid pipes, and fart-cannon exhaust tips (these mostly on the ricer side of town). It's why "butt-dyno" reports are all to be taken with a grain of salt.
Getting back to the KAM, the difference between how the engine runs immediately after clearing the KAM, and once the adaptive learning has done its thing, is related closely to how well the tune has been setup. If the MAF curve and injector slopes are dead-on then short term fuel trims will be hovering around 0.0% and the long term trims (averages of the STFTs) will be at or very near 0.0%--essentially there's nothing to learn.
If however the STFTs are way out either rich or lean then the LTFTs (used in open loop mode)--learned as averages of the STFTs--will also be whacked-out and will be what is applied in open loop.
Generally this is bad and very often is why people with poorly tuned, cobbled together from "pieces/parts", setups see the AFR bouncing all over and difficult to control at WOT.
Then there is that nasty trait we humans all share, placebo effect and its kin. We often "notice" a difference when we expect to notice one, and very whether there is a real difference or not. The opposite holds as well, we often do not notice a real change if we were not expecting change.
As an example, installing a louder intake or exhaust system on a car will make 99.44% of people notice, and believe, that the engine has become more powerful--even when in some instances the opposite is true. This is what sells CAIs, "off-road" mid pipes, and fart-cannon exhaust tips (these mostly on the ricer side of town). It's why "butt-dyno" reports are all to be taken with a grain of salt.
Getting back to the KAM, the difference between how the engine runs immediately after clearing the KAM, and once the adaptive learning has done its thing, is related closely to how well the tune has been setup. If the MAF curve and injector slopes are dead-on then short term fuel trims will be hovering around 0.0% and the long term trims (averages of the STFTs) will be at or very near 0.0%--essentially there's nothing to learn.
If however the STFTs are way out either rich or lean then the LTFTs (used in open loop mode)--learned as averages of the STFTs--will also be whacked-out and will be what is applied in open loop.
Generally this is bad and very often is why people with poorly tuned, cobbled together from "pieces/parts", setups see the AFR bouncing all over and difficult to control at WOT.
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
I see. Thanks Cliffyk. I can still swear though that I can notice a difference between when my battery has been disconnected for more than 5 minutes and when my gauges just randomly sweep due to this battery. But ah well, i'm sorta planning on a new battery sooner or later anyway.