After street tuned, PCM no longer retards timing to 0 under deceleration...??
05-13-2012, 09:08 AM
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After street tuned, PCM no longer retards timing to 0 under deceleration...?? Hi guys/gals,
Last summer I had my Firehawk street tuned by a local recommended tuner. Everything runs great but I just noticed something yesterday while taking it out for the first time this year and the second time since it was tuned. When take my foot off the gas and decelerate while in gear, it no longer retards my timing to ~0 degrees like it used to do. It used to drop the timing and it almost acted like a compression brake when it did, as the car would decelerate even faster. Now when I take my foot off the gas it stays at whatever timing it's at and therefore doesn't decelerate like it did before. Is this something that could have been changed? It's not a big deal, but just curious as to why it doesn't do it anymore, and the only thing I could come up with is it was changed during the tune. I did a quick search as it seems like it may have something to do with DFCO? Anyway, just curious if anybody knows if it's possible to turn this "feature" off and if there's any benefit and/or drawbacks to doing so?
thanks!
Paul
Last summer I had my Firehawk street tuned by a local recommended tuner. Everything runs great but I just noticed something yesterday while taking it out for the first time this year and the second time since it was tuned. When take my foot off the gas and decelerate while in gear, it no longer retards my timing to ~0 degrees like it used to do. It used to drop the timing and it almost acted like a compression brake when it did, as the car would decelerate even faster. Now when I take my foot off the gas it stays at whatever timing it's at and therefore doesn't decelerate like it did before. Is this something that could have been changed? It's not a big deal, but just curious as to why it doesn't do it anymore, and the only thing I could come up with is it was changed during the tune. I did a quick search as it seems like it may have something to do with DFCO? Anyway, just curious if anybody knows if it's possible to turn this "feature" off and if there's any benefit and/or drawbacks to doing so?
thanks!
Paul
05-14-2012, 08:21 AM
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Seems like the tuner tuned out your DFCO and added timing to your decel tables. Even not entering DFCO there still is some timing being retarded so looks like he did both.
The drawback is that you're not saving fuel when decelerating and have to use the brakes more instead of letting the car slowdown itself for free.
The drawback is that you're not saving fuel when decelerating and have to use the brakes more instead of letting the car slowdown itself for free.
05-14-2012, 08:53 AM
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Yes - it's DFCO and yes it can be turned off/on. During tuning, DFCO is usually turned off to avoid having the log pick up the super-lean WBO2 readings that occur under decel, which can throw off other cells when resuming normal fueling.
I'd go back and ask that it's turned back on.
I'd go back and ask that it's turned back on.
05-15-2012, 08:13 AM
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thanks guys. I am waiting to hear back from him. It all makes sense, as he did run a WB and did turn off the MAF so he could dial in the MAF and VE tables. I'm sure he turned it off in order to properly do so.
I know a few years ago I had a throttle positioning sensor go bad, as it wouldn't read 0 TPS at idle. It would not back timing off under decel then either. This was because of the bad TPS though. The lowest the TPS would go was 1, so it thought my foot was never completely off the gas I'm guessing.
I have a ScanGauge that I use and man, does that thing come in handy for observing things that one may not notice without it. That's how I was informed of my bad TPS. I noticed that my TPS was reading 1 when idling.
I plan on having him turn it back on, as I do find myself tapping the brakes more often when on the highway following those that can't seem to keep a steady speed.
I know a few years ago I had a throttle positioning sensor go bad, as it wouldn't read 0 TPS at idle. It would not back timing off under decel then either. This was because of the bad TPS though. The lowest the TPS would go was 1, so it thought my foot was never completely off the gas I'm guessing.
I have a ScanGauge that I use and man, does that thing come in handy for observing things that one may not notice without it. That's how I was informed of my bad TPS. I noticed that my TPS was reading 1 when idling.
I plan on having him turn it back on, as I do find myself tapping the brakes more often when on the highway following those that can't seem to keep a steady speed.
