RPM slow to drop

[marksawatsky]

My engine is a 2013 LHU in a standalone application, using an E39A ECM. It makes tones of power and boost comes up quickly but it has this one little quirk that bothers me. When I have to shift or lift for a corner, the RPM drops too slowly. It's like I have a sticky throttle (but obviously I don't because it's throttle-by-wire). It does it when sitting still or when at speed, doesn't matter. What table can adjust this?

[marksawatsky]

I recently managed to get a tach working, you can see how slow the revs drop in this video

[CDNITE]

Perhaps the DFCO? Have you verified throttle blade position?

[marksawatsky]

Is that something I would see in a log? What should I be looking for?

[marksawatsky]

.throttle response.hpl I attached a short log file where I revved the engine up then dropped the throttle

[T-Man]

This has to do with emissions. Not a whole lot you can do to minimize it and HPT isn't going to provide you with the tools to do it due to legality.

[cobaltssoverbooster]

if i recall in teh lnf the desired torque, optimum torque and pid tables can eliminate this lag. look for tables with similar characteristics to those and you should be able to increase the drop rate some.

its not just emissions related, its also easier on the clutch packs and synchros in the transmissions when downshifting in oem street applications.
there is a table or two in there that can dictate urgency of power requested and if you make it more reactive to throttle input then it will let it fall faster.

[T-Man]

if i recall in teh lnf the desired torque, optimum torque and pid tables can eliminate this lag. look for tables with similar characteristics to those and you should be able to increase the drop rate some.

its not just emissions related, its also easier on the clutch packs and synchros in the transmissions when downshifting in oem street applications.
there is a table or two in there that can dictate urgency of power requested and if you make it more reactive to throttle input then it will let it fall faster.

I tried and had zero success. I asked about it and was told its mostly related to emissions. Clutch/tranny protection makes sense too

[marksawatsky]

Thanks for the help guys, it gives me some things to try and I'll send it to my tuner (Bad News Racing) and see what they make of it

[steelmesh]

Not sure if this is related, my E78 will "hang" my rpms, if I tap the clutch (to make the clutch pedal switch) it will drop rpms. Basically, when the rpms are hanging, the timing advance is something like 40 degrees, when I make the clutch switch timing drops to close to 0 degrees and the rpm drops then.

Could you have too much timing at high RPM with low air flow?

[marksawatsky]

That's an interesting idea, I'll see if I still have the clutch wire and do some experimenting

[steelmesh]

That's an interesting idea, I'll see if I still have the clutch wire and do some experimenting

I guess I was alluding to at least see what the timing is doing and maybe adjust it and see what happens. My clutch switch comment was just kind of exposing that a input was provided to the ECU, then it changes the timing strategy, I don't really understand it...only understand the symptoms at this point.

[marksawatsky]

I attached a log and the timing does back off when I drop the throttle. I tried the top of clutch wire and the depressed clutch wire and neither of them made any difference.

[marksawatsky]

I think I solved the problem, the line for the bypass valve was hooked up before the throttle body so it wasn't seeing any vacuum when I chopped the throttle. It's hooked up after the throttle body now and the rpms drop much quicker. I expect the boost to come up much quicker when I get back on the throttle, but I have to wait a month to test that.

[coryk]

I think I solved the problem, the line for the bypass valve was hooked up before the throttle body so it wasn't seeing any vacuum when I chopped the throttle. It's hooked up after the throttle body now and the rpms drop much quicker. I expect the boost to come up much quicker when I get back on the throttle, but I have to wait a month to test that.

Please keep us posted, I'm experiencing similar issues with my standalone 1.4. Thanks.