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View Full Version : Had a quick question about choking on deceleration.

oricale
04-10-2013, 09:56 PM
I think I fixed the smoking issue(for the most part and did a few other things for this season)..BUT

I have always had this issue:....Upon releasing the gas pedel and allowing the car to slow itself by the gear with no brake on..and after a bit of deceleration at high rpm's its starts to choke on itself and sputter..all this goes away with a minimal amount of gas pedal.


Any ideas??
scottfab
04-10-2013, 11:02 PM
TB plates or IAC sticking.
oricale
04-10-2013, 11:10 PM
Actually I dont think the IAC functions correctly...a whileago we disconnected it and nothing happenend!...hmmmm
XfireZ51
04-10-2013, 11:28 PM
Choking? What does at mean? Shutting off? Does it happen at a particular mph?
oricale
04-10-2013, 11:30 PM
Choking like it cant breath or not getting gas maybe.

not sure of mph...its usually after about 3-5 seconds of deceleration
Hib Halverson
04-10-2013, 11:32 PM
Actually I dont think the IAC functions correctly...a whileago we disconnected it and nothing happenend!...hmmmm

If you unplug the IAC while the engine's running, it will hold its setting which might seem like nothing happened, at least for a short while.
oricale
04-10-2013, 11:37 PM
OK Hib, pull it while its running and leave it off longer?

before when I had a smoke issue, the idle would fluctuate, currently is rock steady at 950 rpm.I thought that was a indication of a nad IAC.
Fully Vetted
04-11-2013, 01:48 AM
What was the smoke issue?
XfireZ51
04-11-2013, 09:38 AM
What mods on the motor to have a 950rpm idle?
tomtom72
04-11-2013, 09:51 AM
Choking like it cant breath or not getting gas maybe.

not sure of mph...its usually after about 3-5 seconds of deceleration

If you have a GM EPROM (?) then the program has DFCO, it's a fuel cut off under compression braking. Could this be what you are feeling? I forget at what rpm it comes "in", but it's closer to idle speed than not, say about 1100 or maybe less....I don't notice it any longer as I guess I'm used to it now. When I first got the car I noticed it right away. Just a thought.:o

:cheers:
Tom
XfireZ51
04-11-2013, 10:59 AM
Tom,

That's the reason I asked about mods. DFCO is usually disabled in re-done cals because of stalling on modded motors.
GOLDCYLON
04-11-2013, 11:39 AM
Tom,

That's the reason I asked about mods. DFCO is usually disabled in re-done cals because of stalling on modded motors.

AMEN
secondchance
04-11-2013, 11:48 AM
I think I fixed the smoking issue(for the most part and did a few other things for this season)..BUT

I have always had this issue:....Upon releasing the gas pedel and allowing the car to slow itself by the gear with no brake on..and after a bit of deceleration at high rpm's its starts to choke on itself and sputter..all this goes away with a minimal amount of gas pedal.

Any ideas??

Dempsey,

Check your MAP hose. If it's a soft rubber hose replace with rubber fitting/hard plastic (whether OEM or fabricated).
Hog
04-11-2013, 04:49 PM
Sounds like DFCO to me, esp with a touch of throttle correcting the "issue".

peace
Hog
XfireZ51
04-11-2013, 05:03 PM
Sounds like DFCO to me, esp with a touch of throttle correcting the "issue".

peace
Hog

The stock calibration calls for enabling DFCO at 1500rpm and disabling at 950. So your idle is set right at about the point the ECM is looking to exit
DFCO. Does it feel like its oscillating? Moving the TPS to 1.95% open takes it out of DFCO. Does that sound like what's happening to you?
tomtom72
04-12-2013, 05:51 AM
Tom,

That's the reason I asked about mods. DFCO is usually disabled in re-done cals because of stalling on modded motors.

Thank you Dom! I just learned something new. :handshak: I had no idea about DFCO and modded motors.


I wonder is DFCO related to the backfiring under compression braking that seems to crop up on LT5's with headers?

:cheers:
Tom