low RPM hesitation and rough tip-in enrichment

FlashPro questions & answers specific to the 2006-2009 (US, UK, Asia) S2000
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shind3
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low RPM hesitation and rough tip-in enrichment

Post by shind3 » Mon Jun 30, 2014 8:14 am

My completely stock 2006 AP2 has an intermittent hesitation most noticeable in 1st and 2nd gear when starting off from a stop at a traffic light at a leisurely pace. I have read countless threads on this topic and have come to the conclusion that it is not normal even for a DBW car. Between 2500 and 3500RPM, I'll sometimes get a massive dip in power followed by a sudden increase. This doesn't always happen though so it's not a ignition timing issue and it certainly doesn't happen if I go WOT (Open Loop).

It feels like the tip-in enrichment at low delta TPS is too lean and the O2 sensor lags a bit to pick up this lean drift and then suddenly adds enough fuel to bring the power back. This is something I know how to tune out on a Subaru with modified injectors but my S2000 is completely stock and shouldn't be doing this. Even when the car is decelerating with the injectors off, and you gradually increase from 0% APP to bring it out of injector cut mode, the transition to injector on is too harsh in my opinion. It should be smooth almost seamless. It's almost like the injector latencies are off but the whole thing is stock!

I tried logging with Torque (Android Bluetooth OBD2 logger) and I can see a Fuel Trim (not sure if it's ST or FT) hover at less than 2% while cruising and then spike to as high as 8% during tip-in. Then during throttle lift, it goes as much as -8%. The logging speed of this thing is quite slow so I'm sure I'm missing some lines of data.


So, my question is, is this a mechanical issue or do all AP2s behave this way? With Subarus (MAF & Speed Density, cable & DBW), I am able to tune for a perfectly smooth transition on/off throttle and tip-in enrichment with good injectors like stock or ID1000 etc. Is this something that can be fixed with FlashPro or do I need to fix a mechanical issue?


Thanks for your input.

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Hondata
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Re: low RPM hesitation and rough tip-in enrichment

Post by Hondata » Mon Jun 30, 2014 9:39 am

Our S2000 never drove like that, and others I've driven did not either.

+-8% trims are typical for a stock vehicle. However, it sounds like there might be a slow acting o2 sensor or similar problem which is causing the hesitation.

If there is a problem, I would not recommend using a FlashPro to try and fix the underlying problem. In that case we'd recommend that you went back to stock, fixed the problem, then use FlashPro.
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shind3
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Re: low RPM hesitation and rough tip-in enrichment

Post by shind3 » Tue Jul 01, 2014 11:33 am

Thanks for your reply. I guess it's possible to have this issue without DTCs.

I suppose changing the O2 sensor at 91K miles wouldn't be a total waste even if it was fine.

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Hondata
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Re: low RPM hesitation and rough tip-in enrichment

Post by Hondata » Tue Jul 01, 2014 12:08 pm

The other thing I've seen is a lot of throttle body failures, but normally they generate a code.
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shind3
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Re: low RPM hesitation and rough tip-in enrichment

Post by shind3 » Thu Jul 31, 2014 1:48 pm

I readjusted my valve lash and set it to 9/11 thou (Intake/Exhaust) from mostly 9 thou Intake to varying 10 to 12 thou Exhaust. There is still a huge dead spot at <3K RPM but it feels like it hesitates less? I don't know, it's probably a placebo effect. Car still feels dead when tipping in throttle at low RPM at first then suddenly picks up.

I then changed out the O2 sensor to a new Denso unit and observed no change.


I wish I could log the ECU, isolate the issue by examining the data, then buy a FlashPro to fix if needed. I really don't want to spend $700 on just a datalogger. Is there any such help you guys can offer here? By that I mean, can I get/buy a utility to datalog the ECU only? I already have a CANBUS compatible USB adapter. See Tactrix OpenPort 2.0. http://www.tactrix.com/index.php?option ... &Itemid=53

bunger78
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Re: low RPM hesitation and rough tip-in enrichment

Post by bunger78 » Fri Aug 01, 2014 8:39 am

Before tuning, my engine had some inaudible knock that would cause under aggressive knock control, and during these times, I found that I would get something like you're describing.

I used Hondata's suggested method of overlaying knock count on the ignition map and pulling timing where I saw frequent knock counts. With this technique I was able to keep the knock control in check and eliminated the "flat spots".

Even just a OTS tune for these cars makes a heck of a difference, and the resell value on a FlashPro is pretty good, so it's a low risk investment. I know a few people that are selling used units if you'd like their info.

shind3
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Re: low RPM hesitation and rough tip-in enrichment

Post by shind3 » Wed Aug 06, 2014 7:41 am

Yes, please let me know of the people selling a used FlashPro. Thanks.

Yeah, the stock tune definitely seems very jumpy between 1K and 3K RPM. It gets better after that. The transition between injector on/off also ought to be smoother. The throttle pedal is also too sensitive at low opening angles/RPM. Ideally, it should correlate linearly with engine power. Right now, it's very front loaded.

And yeah, because it doesn't do it all the time, your explanation seems plausible. It does feel exactly like a lot of timing got suddenly pulled.

daverx7
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Re: low RPM hesitation and rough tip-in enrichment

Post by daverx7 » Wed Aug 06, 2014 3:11 pm

I'm going to watch this thread as I might have this issue too.

shind3
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Re: low RPM hesitation and rough tip-in enrichment

Post by shind3 » Thu Aug 07, 2014 6:40 am

I haven't received my FlashPro yet but thought I would do some homework in the meantime.

I opened up a ROM (stock?) I found on here in FPM and analyzed the timing maps. I copied them into Excel, added the Main Ignition to the Knock Ignition Limit maps, then took the minimum between it and the Main Ignition map to get the following table.
Image
This is the maximum timing the car would run on sufficient octane. I noticed two spots where the timing changes very rapidly over a short period of time. One is at higher load around 1500RPM and the other is at around 2750RPM at almost all loads. That's 5 to 8 degrees in 500RPM. That is way too steep!

So, is there room to increase timing at 1300 and 2600RPM a bit to help smooth the transition from RPM cells before and after? Or am I better off trying to reduce timing in the 1800 and 3100 range? The F22 probably hits peak VE at 1300, 2600, and 5200RPM which correlates with the reduced timing in those areas relative to surrounding cells. I am hoping if I always run 93 octane, I can smooth out the timing map a bit.

Can anyone else who has experience with this engine comment on which approach is more likely to work?

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