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Acceleration enrichment, driving me crazy

PostPosted: Wed Oct 12, 2016 5:04 am
by ChrisAudi80
This issue has been driving me up the wall lately. I have obviously have no idea what I am doing wrong.

When I transition the throttle, off (goes rich of course) then back on, the motor just goes lean (like 1.2-1.5) and bogs. This is on small throttle inputs too.
I have dTPS enrichment at 50% and it still does this. Warm or cold, same. Are my EGO closed loop settings wrong? Is my VE table totally wrong? I have been logging and tuning the VE table for weeks.
See attached zipped log. Please help... :bangshead:

Re: Acceleration enrichment, driving me crazy

PostPosted: Wed Oct 12, 2016 1:06 pm
by loxxrider
First of all, you can't tune the car properly with EGO correction on. EGO is not quick enough to respond to problems in AFR without a good feed-forward map (the VE table) to work with in order to "predict" what is going to happen. It can only correct so much, so quickly and if the baseline VE table isn't right, it will wont be able to help enough to make any difference.

That isn't the overbearing issue here, but it needs to be addressed before you'll be able to get this thing really dialed in.

As far as the accel enrichment goes, don't be afraid to really bump it up. Put 200% in if you have to. Just make sure that the cells being activated in the VE table are actually producing a reasonable AFR during steady-state operation. Then the only thing you've really got to change is the accel enrichment. Turn it up as much as you want. You aren't going to hurt anything. 50% is nothing during high dTPS/dt events.

Re: Acceleration enrichment, driving me crazy

PostPosted: Wed Oct 12, 2016 10:10 pm
by ChrisAudi80
loxxrider wrote:First of all, you can't tune the car properly with EGO correction on. EGO is not quick enough to respond to problems in AFR without a good feed-forward map (the VE table) to work with in order to "predict" what is going to happen. It can only correct so much, so quickly and if the baseline VE table isn't right, it will wont be able to help enough to make any difference.

That isn't the overbearing issue here, but it needs to be addressed before you'll be able to get this thing really dialed in.

As far as the accel enrichment goes, don't be afraid to really bump it up. Put 200% in if you have to. Just make sure that the cells being activated in the VE table are actually producing a reasonable AFR during steady-state operation. Then the only thing you've really got to change is the accel enrichment. Turn it up as much as you want. You aren't going to hurt anything. 50% is nothing during high dTPS/dt events.


Thanks for replying, Chris.

Yes, I realize EGO can only do so much. All the reading I have done says the VE table must be very close before tuning accel enrichment.
Which is why I am skeptical with some of the VE statistics tool results. The curve needs to be smooth, so I only use it as a guide now.

Last night, I bumped up the dTPS and the RPM enrichments a lot. That actually worked. It then went quite rich so I am getting somewhere, I think. It was much more responsive. I have attached pics of the settings I used last night. I turned it down a tad because it dropped down to .76 or moe and did a rich bog.

Re: Acceleration enrichment, driving me crazy

PostPosted: Wed Oct 12, 2016 10:17 pm
by ChrisAudi80
I should add that I'm still learning how to interpret the log. I understand how dTPS works and know that there is a delay of about 0.3-0.5sec before something happens. IIUC accel RPM adds fuel with (quick?) changes in RPM. Not sure how to see that. I guess I need to log separately. One log with RPM only and another with dTPS only.

Re: Acceleration enrichment, driving me crazy

PostPosted: Thu Oct 13, 2016 12:08 pm
by loxxrider
To be honest I don't use the rpm enrichment. I would just tweak the dtps/dt until you eliminate any spikes. That should be all you need.

Re: Acceleration enrichment, driving me crazy

PostPosted: Thu Oct 13, 2016 11:20 pm
by ChrisAudi80
loxxrider wrote:To be honest I don't use the rpm enrichment. I would just tweak the dtps/dt until you eliminate any spikes. That should be all you need.

I see! Do you put RPM enrich at 100 or 0? The worst area where I have lean bogs/chokes is the 700-1700rpm and 20-76kpa cells. Decel going to accel.
Very hard to tune properly. I read this write up ( http://www.enginebuildermag.com/2012/01 ... ooth-idle/ ) many times and use the tips. They helped.

Re: Acceleration enrichment, driving me crazy

PostPosted: Sat Oct 15, 2016 5:20 am
by loxxrider
In that case you could use the rpm enrichment between the two rpm you mentioned, but it's really for taking dtps/dt fueling out a bit at higher rpm. It isn't needed as much there. What happens if you add more fuel in those parts of the dtps table?

Re: Acceleration enrichment, driving me crazy

PostPosted: Sat Oct 15, 2016 5:21 am
by loxxrider
I would just leave your rpm enrichment as they are for now until you notice problems revving while coming off of high rpm.

Re: Acceleration enrichment, driving me crazy

PostPosted: Sat Oct 15, 2016 9:26 am
by ChrisAudi80
I don't really have (lean) problems at high RPM (4000+). Its the heavy traffic driving at low RPMs. It's probably because I don't have an idle control valve. I am waiting for the VEMS US boys ( https://www.facebook.com/VEMSUS/photos/ ... =3&theater ) to finish developing a new PCB specifically for the two-way VR6 TB IAC motor.
With AC on, my engine idles at 670, w/o AC 1050.

It was a lot better today, though. I will try removing RPM enrich and just use dTPS. I forgot to ask: What happens when there is negative dTPS?
Does it take fuel out?

Re: Acceleration enrichment, driving me crazy

PostPosted: Sat Oct 15, 2016 9:29 am
by ChrisAudi80
loxxrider wrote:. What happens if you add more fuel in those parts of the dtps table?

It works well at mid to high rpm.

Re: Acceleration enrichment, driving me crazy

PostPosted: Mon Oct 17, 2016 2:13 am
by ChrisAudi80
Another potential issue is the Siemens Deka min. stable pulse width: 1.9ms. I see 1.6-1.7ms when idling w/o AC.
Spent some time today with EGO off tuning the 660-2500rpm 30-50kpa range. It wasn't far off, but the low PW did not help.

Might swap in a 2.5bar FPR (again) to increase the PW.