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Minor hesitation coming off idle to part throttle

Armitage

Well-known member
Joined
Oct 16, 2003
Messages
715
Location
Herndon, VA
I've been noticing a very slight hesitation in the car when I roll into the throttle from a stop under normal daily driving conditions. It only happens sometimes. Basically the car is idling and the very instant you apply any throttle, the revs dip for a fraction of a second before they start to climb again. It doesn't really affect anything but it's super annoying. Stock healthy motor, e16g turbo, 550cc injectors, MAF-T in blow-through, lightweight flywheel, b-shafts removed, keydiver chip set for A/F changes, coil-on-plug.

So first we've got the point in time right before the throttle is blipped. I had just cold started the car so it's idling fine at 1250.



.2 seconds later, 22% throttle, revs have dipped to 1219, timing has dipped as well. Injectors have fired a little more, airflow remains constant.



.2 seconds past that, I've already closed the throttle, but revs are now starting to increase.



Any ideas what's going on would be helpful. I have no idea where to start with this. I've calibrated the TPS, pressure tested the system, everything else runs great. Car makes great power, runs smooth, revs perfectly all the way through the band...
 

Lonewolf64

Well-known member
Joined
May 17, 2006
Messages
1,197
Location
Birmingham, Alabama
Have you tried replacing your COP with a stock coil pack to see if the problem persists?
 

Armitage

Well-known member
Joined
Oct 16, 2003
Messages
715
Location
Herndon, VA
I no longer have a stock coil pack or plug wires to test with :p

Since the car is otherwise running fine I don't think there's "anything wrong" with the COP. Assuming that it's working as-designed, the next logical question is: does anyone else who runs a COP experience this problem? Conversely, if we assumed that something is in fact wrong with the COP, what possible failure mode would cause these symptoms but not manifest themselves in any other form?
 

Armitage

Well-known member
Joined
Oct 16, 2003
Messages
715
Location
Herndon, VA
I want to say that all three fuel trims were one of 91 and 93 when I looked (but didn't log). At the time of these logs I had decreased the SAFC 2% across the board but didn't run the car long enough to see where that got me.
 

If all your fueltrims are low, it would be better IMHO to raise the base fuel pressure slightly, if you have an AFPR. The hesitation that you are experiencing could be a lean spot the car is hitting when it transitions from closedloop to openloop.
 

Armitage

Well-known member
Joined
Oct 16, 2003
Messages
715
Location
Herndon, VA
Unfortunately I don't have an AFPR on this car. Maybe something to look into one of these days. I'll do a little SAFC tuning and get those trims closer to 100 and see if that helps any though. Thanks!
 
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