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Rpm surges in closed loop but not open

Posted: Tue Aug 16, 2016 6:47 pm
by boosted crx-r
I can hold the throttle at 2000 rpm in closed loop and it surges about 600rpm difference but as soon as I switch to open loop while holding the pedal steady it smooths out and no longer surges. Could this be my wideband o2 going bad or something else?

Re: Rpm surges in closed loop but not open

Posted: Wed Aug 17, 2016 9:22 am
by Spunkster
look at your long and short term fuel trims when doing this and you will probably see what is happening.

Re: Rpm surges in closed loop but not open

Posted: Wed Aug 17, 2016 5:47 pm
by boosted crx-r
can you take a look at the trims and give me any recommendations on which way to go? these datalogs are while im in nuetral holding the throttle at a 2000rpm. it looks like a roller coaster in closed loop,

Aebs 84.5mm sleeves with typer head skunk 2 pro series valve train edelbrock intake and throttle body

heres the tune. i just started messing with it so i know its not perfect
black hatch.skl
(41.95 KiB) Downloaded 64 times
datalog in closed loop with wideband
closed loop.s3d
(118.74 KiB) Downloaded 82 times
open loop
open loop.s3d
(153.77 KiB) Downloaded 65 times

Re: Rpm surges in closed loop but not open

Posted: Wed Aug 17, 2016 5:56 pm
by boosted crx-r
it also does the same thing at any rpm level while im driving. makes the car surge

Re: Rpm surges in closed loop but not open

Posted: Thu Aug 18, 2016 7:22 am
by Hondata
Your problem is the wideband is slow to respond. With the closed loop datalog graph the lambda & short term trim. The lambda lags the short term trim by around 0.7 seconds. Normally the lag will be 0.2s or less.
Ideally you should find out why the wideband is slow, but you could try reducing the closed loop rate of change values so that short term trim changes more slowly.

Re: Rpm surges in closed loop but not open

Posted: Thu Aug 18, 2016 8:21 am
by boosted crx-r
Ok...I will give that a shot. Is there a point where lowering the short term adjustment will start harming anything on the tune. Would I essentially be running in open loop if the values are set to low? I am running an old box style plx m300 so as you suggested it might be wearing out on me.

Re: Rpm surges in closed loop but not open

Posted: Thu Aug 18, 2016 10:10 am
by Hondata
The disadvantage is that the trim will be slow to make any fuel corrections. Pull the o2 and clean it in white vinegar for an hour or so. Otherwise replace the o2, but wideband lambdas are so inexpensive now you might consider a new wideband.

Re: Rpm surges in closed loop but not open

Posted: Thu Aug 18, 2016 5:20 pm
by boosted crx-r
Should I change the slow rate of change or the fast rate of change boxes? Bought a new O2 but it didn't help. Gonna get a new wideband now I guess

Re: Rpm surges in closed loop but not open

Posted: Fri Aug 19, 2016 8:32 am
by Hondata
Try one, then the other, and see what gives the lowest short term trim over a couple of seconds.