Idle Issue - Engine dies when returning from high rpm

FlashPro questions & answers specific to the 2006-2009 (US, UK, Asia) S2000
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Minor Threat
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Joined: Fri May 02, 2014 9:09 pm

Idle Issue - Engine dies when returning from high rpm

Post by Minor Threat »

- FP-S2K-US-30962
- Flashpro 1.8.2.0
- Factory ECU
- Built engine, turbo kit, ID1000cc injectors, Inlinepro fuel rail and return-style fuel system, Hondata 4bar map sensor

I'm having an issue with the warm idle on the car, no matter what I set the idle tables to in Hondata, it will not catch the idle on decel and the engine dies. AFR are close to stoich if not a tiny bit richer. If I pedal the car to keep the engine running and slowly lower it down to idle, it will idle very low for a minute and then slowly return to the correct idle. I can watch the Tplate numbers increase as the engine slowly comes back to the correct idle.

I have tried creating a buffer in the low cam ignition table to catch the idle, with no luck. I have varied AFR around within reasonable limits with no change. The issue only happens when the car is warmed up completely, with a cold high idle it's fine.

Attached are a datalog of the issue with the car almost warmed up, it doesn't die but idles very low, and the most recent cal.
Attachments
s2000id1000.fpcal
(9.03 KiB) Downloaded 181 times
s2000idle.fpdl
(27.58 KiB) Downloaded 167 times

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Hondata
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Hondata »

You're running in open loop, so we can't tell what the fuel trims are like. Check the fuses as the ECU does go through a idle learn process which the ECU will go through, and if the power to the ECU is lost with ignition off it will never retain the settings.
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Minor Threat
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Minor Threat »

If the AFRs are good, and the car is in open loop, what bearing does the fuel trim have on the issue? Prior to the run the idle AFR are fine, I can also free rev the car in neutral and have it die as well.

I've attached another log from a WOT pull on the dyno, followed by me applying throttle to keep the car running and then finally letting off and having it die. I then had to crank it over twice before it caught enough to stay running. I can watch the TPlate numbers go up as the idle returns to normal. Is there any way to adjust the base TPlate table at 0 TPpedal?

I will check fuses and report back.

EDIT

Fuses are good.
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s2000lowcam-140503-002.fpdl
(27.41 KiB) Downloaded 157 times

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Hondata
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Hondata »

Minor Threat wrote:If the AFRs are good, and the car is in open loop, what bearing does the fuel trim have on the issue?
Because I'd like to see what the mixture is and how good the tuning is. The manifold pressure is 46 kPa at hot idle, so something is not right, and it likely is mixture. There also is a bad oscillation at idle.

I don't think that chasing the response of the throttle is the right path - it's not the cause. I have seen S2000 throttle bodies die quite regularly, but they usually throw a code when they do. I would start by looking at the injector dead times & fuel tuning. If they look inconsistent then I'd look at the o2 sensor first (eg slow response from a cold start).
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Minor Threat »

The mixtures are very close to stoich, and varying them doesn't make a difference to the issue. I can set them to 12:1 all the way to 16:1 and it will still do the same thing. This is both prior and post to revving it up.

The dead times are from the Hondata ID1000 basemap, how close are they?

Is there a way to test the throttle body?

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Hondata
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Hondata »

Given the high manifold pressure at idle (46 kPA is very high; 30 kPa is normal), something is either mechanically wrong or the o2 sensor is lying. Is it not possible to switch on closed loop and do a datalog?

The ID dead times look ball park ok. You can test by datalogging what happens when cruising in 3rd gear @ 3000 rpm and then reducing throttle very slowly until the injectors cut off. If the dead times are correct then the short term trim will stay flat.

The only way to test the throttle body is by substitution. I do not believe that the throttle body is the problem at this point.
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Re: Idle Issue - Engine dies when returning from high rpm

Post by Minor Threat »

Sadly no, there are no o2 sensors on the car. All I have is the dyno wideband which reads accurately on other vehicles with closed loop functions.

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Re: Idle Issue - Engine dies when returning from high rpm

Post by Hondata »

You need to check the AFR while driving to diagnose this problem.
Hondata

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