Wondering if anyone else has ever seen this problem? When driving at any speed, more noticably at slower speeds my car will have a quick burst of power after I have lifted off the throttle. It is very short burst but it is enough to change the load on the driveline. Is it the inj dwell that controls how long after lifting the injectors continue to burst fuel?

My throttle body has the secondary butterflies removed, and the engine does have a fairly aggresive port that I would call street/track ported.

Thanks!

 

Mine does the same thing. It likes to buck when the throttle is barely cracked. It does the same bump about a quarter second after I lift when coasting down a hill.

I don't know why. Maybe somebody will chime in.

 

I think its a combination of the little fuel its getting vs the drivetrain , doesi t happen when you disengage the clutch?


or just when you engine brake

this is more then likely engine braking , the drivetrain is rotating the engine , faster then it should be because of a/f in it and that slight bucking

I cant say if its combustion by what little air/fuel is getting in , or if its just compression resistance from the engine vs the drive train

These are all uneducated guesses but its what i always thought it was.

 

Dashpot holding the throttle open. Remove it if it bothers you or try adjusting it.

thewird

 

You need to provide datalogit logs.

The acceleration shock is most likely a tip-in fuel issue/hesitation. I have posted extensively about this; do a search for threads I have started. It can be improved but for the most part it can't be 100% eliminated. This is due to the way the PFC software is; IMO it's an injection timing issue more than anything else, and the PFC doesn't have injection timing control capability.

There isn't a whole lot you can do about deceleration shock on a modded car with a PFC besides maybe adjust the dashpot. Normally you use fuel cut staging and spark retard control to reduce deceleration... there are delay timers and torque-based logic that can be used. That's not something the PFC can really adjust. It's OEM-grade software required for this.

 

My bump on decel actually shows up as a quick flash on my aquamist 2D "injection" light. It flashes quickly after being off. A datalogit is On my things to purchase as I work the cobwebs out of the old girl.

 

I took it out tonight and was messing around with timing split and the tip in fuel I have. TPS vs Inj at the first stage is 1.047 which my car likes because of the port job and throttle body mods. And changing the timing did not help me much either, it did get a bit softer when I lowered the timing down from 32 to 22. Perhaps that could be an area of further improvement.

I will have to look into your recommendations arghx, thanks.

I did notice when I was watching my timing on the map watch that my leading timing goes from 31 to 7 to 31 at the exact moment that the lurching occurs. But I'll be damned if I can find an area in my Datalogit screens where I could adjust such a setting.

Attached is my .dat

 

I went to adjust my Dashpot, which was not touching at all BTW, and found that I need to set my primary butterfly differently. I have it held open to the point that the dashpot can barely touch even when all the way tightened. Which will have other OPS checks involved after I funk up my TPS at idle voltages.

More to come on that as well. Thanks.

 

I'm currently trying to solve this, anyone have new thoughts? Original posters have any new info? I can watch my injectors duty cycle go down to about 9% then just drop off to 0 instantly, accompanied by a lurch. When accelerating from zero throttle, they jump right up to 9% if I even slightly touch the throttle. It seems like I need to just make the throttle taper on/off on small amounts of TPS change, is there anywhere to adjust this? Maybe a value >1 at the lowest set of points in the TPS vs INJ table?

I'm going to try adjusting my INJ for vacuum, maybe they're too high so touching throttle in that area causes that 'jump' in injector duty.

 

I have a Wolf EMS v550 and have this problem too. I was looking in my software for settings that might affect this lurching, and see that there is a fuel setting under my Overrun Fuel Cut section called "Recover Fuel Pulse Activate" - with values for a count and millisecond TICs. The help says "In some cases the engine requires a small amount of fuel when the "overrun fuel cut" turns off. Recover fuel can add a small amount of fuel to create a smooth transition from "on" to "off". Maybe the PFC has a similar setting?