Help with surge after h/c swap
Thread Starter
Joined: Dec 2003
Posts: 2,152
Likes: 0
From: Virginia Beach, Va
Help with surge after h/c swap I just did my h/c swap a couple weeks ago. We just tuned the car the other night. Everything seems great except Im still getting a little bit of surge when coming to a stop or cruising thru a parking lot at 5-10 mph. Idle air is dialed in and we looked at the throttle follower and throttle cracker. Can someone chime in and tell me if theres something specific we should look at to remedy this problem?? Thanks a bunch
If the airflow tables are right, start by pulling timing tin the area you get the surge in. Sometimes you have to pull it low, but H/C cars don't seem to need as much down low as factory. If RAF is right and the car isn't lean, timing generally fixes or greatly helps.
Having the low end mixture too fat makes the idle loop too
slow and it surges more. I would try taking 10% and 5% off
the 400 and 800RPM VE table columns, see how that plays,
keep shaving at them until it hurts more than helps. When
you tune by the O2s down there, with a cam, your indicated
stoich and your true chemical balance are not the same
thing.
I believe that the MAP dimension may want playing-with, I
am pretty condinced I have a fuel-loop oscillation that is
MAP, wrong airflow, wrong fuel, bugger the MAP, repeat
kind of action (I locked down every thing with bidirectional
controls and it would stil yo-yo). A better idle adaptive spark
profile was what I used to settle it down but it isn't truly
right. Just tolerable. Except with the A/C on.
slow and it surges more. I would try taking 10% and 5% off
the 400 and 800RPM VE table columns, see how that plays,
keep shaving at them until it hurts more than helps. When
you tune by the O2s down there, with a cam, your indicated
stoich and your true chemical balance are not the same
thing.
I believe that the MAP dimension may want playing-with, I
am pretty condinced I have a fuel-loop oscillation that is
MAP, wrong airflow, wrong fuel, bugger the MAP, repeat
kind of action (I locked down every thing with bidirectional
controls and it would stil yo-yo). A better idle adaptive spark
profile was what I used to settle it down but it isn't truly
right. Just tolerable. Except with the A/C on.
Thread Starter
Joined: Dec 2003
Posts: 2,152
Likes: 0
From: Virginia Beach, Va
well, its mainly when the car is either coasting thru the parking lot at 5-10 mph or when coming to a stop. once the car stops, the surging will cease after a second. so its not really idle surging, but when slow rolling or coming to a stop. help fellas!!! I dont have tuning software and my tuner is really busy...he doesnt have a lot of time to spend with me. i dont know anyone else around here though
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Originally Posted by Raise
well, its mainly when the car is either coasting thru the parking lot at 5-10 mph or when coming to a stop. once the car stops, the surging will cease after a second. so its not really idle surging, but when slow rolling or coming to a stop. help fellas!!! I dont have tuning software and my tuner is really busy...he doesnt have a lot of time to spend with me. i dont know anyone else around here though
Your problems when coasting (off throttle) are most likely related to throttle cracker assuming desired idle airflow (Base RAF), and timing/AFR are correct (14.5:1~15.5:1/~23* at idle) - especially since it goes away once you come to a stop. Throttle cracker is MPH refereneced. Had it been a problem with on-throttle surging, I'd point to throttle follower as that is TP% referenced.
Last edited by SSpdDmon; Aug 15, 2007 at 09:01 AM.
Idle and throttle cracker both try to set up a particular airflow.
The airflow vs IAC relation that the airflow loop has to use, is
not really crisp if the motor is dogged by long fuel, short spark
etc. The RPM "outer loop" for idle just adds more laggy baggage.
Review the throttle cracker table and make sure it looks like a
smooth "soft landing" and not a bunch of spikes and divots.
Those will destabilize the idle (rolling idle) as you traverse them.
The airflow vs IAC relation that the airflow loop has to use, is
not really crisp if the motor is dogged by long fuel, short spark
etc. The RPM "outer loop" for idle just adds more laggy baggage.
Review the throttle cracker table and make sure it looks like a
smooth "soft landing" and not a bunch of spikes and divots.
Those will destabilize the idle (rolling idle) as you traverse them.
