Stalling under deceleration

[zrated]

I've had this problem on quite a few cars i've tuned with nistune... It's such a pain the the backside and I really want to know why it keeps happening?

If I rev the car in neutral to about 3-4k it will idle fine, anything over that and the car will stall... the revs drop down under 600rpm and the car just dies.

Can someone tell me in plain english what tables i need to modify to get it to work?

Is the car overfueling or running too lean on decel?

Do I have to adjust fuel or timing? Where do I do it in the software and how?

Is this ECU related or mechanical?

The car is an s13 with a stock RB20DET, standard injectors, standard afm, bigger turbo, with high mount manifold and cooler.

[Matt]

There may be a neutral Rev limiter for that vehicle. Some of the other types of ECUs have known neutral rev limiters

[zrated]

stalling under deceleration has something to do with a neutral rev limt?

[Matt]

If there is a neutral rev limiter and you hit it, then i would expect it to cut fuel. Since you are saying that this problem is only occurring in neutral? But you are saying its not hitting a cut, and only just a cut of fuel on decel?

The standard fuel/cut recover tables are only used when speed is above 20km/h typically so it cant be those.

As for other deceleration enrichment tables, not sure

If you log the problem via consult on the vehicle, what is the injector pulsewidth looking like when the vehicle is decelerating with this condition. It is something I would have to repeat and investigate

The log will tell me a somewhat about whats happening...

[FHCRSky]

Look at the AFM voltage.

HKS EIDS -

http://www.hksusa.com/products/?id=2175

Moving AFM away from front of turbo with a longer intake pipe can reduce the reversion.

In some cases the TPS is not touching the idle contact or TPS is faulty and voltage is lower than normal.

[Matt]

We had a discussion in another thread
viewtopic.php?t=606

Reving and then letting go resulting in reversion (AFM reading extra voltage). If you log this you will see a spike in the AFM voltage as the TPS is released. More of a mechanical fix rather than something you can map around

You would also see this issue in gear as well right?

[FHCRSky]

From what I understand reversion is due to turbo slowing down and can be caused by BOV not venting enough air or not venting quick enough.

Can buy a Synchronic BOV that doesn't have a diaphram (faster reacting) and can vent to atmosphere with engines that have AFM's -

http://www.youtube.com/watch?v=U0R1KvQRk84

There are some problems with them at higher boost levels, etc (teething problems), otherwise it's a good product to solve stalling problems -

http://synapseengineering.com/smf/index ... topic=89.0

Synchronic BOV is the only BOV that I know of that can solve this stalling problem. They won a best new product award at Sema for BOV, wastegate -

http://www.synapseengineering.com/

Recirculating the BOV is another fix. It seems factory recirculates BOV for a reason.

[Rob280z]

Hi guys,
I am new to this forum as I just got Nistune about 6 months ago.

Sorry to resurrect this post but I am having a similar issue.

When I let off the throttle either while driving and shift into neutral or while stationary my car will stall and die. I have to feather the throttle to keep my car running. I could rev the motor to 1.5k or 6k and let off and the car will die it does not matter. I have a rb20det in a 1977 datsun 280z. I have the stock injectors, stock turbo, stock throttle body and stock MAF. I do have 3" intercooler piping, front mount intercooler and forward facing intake. I am using a aftermarket FPR set at 43 psi at idle when open to the atmosphere. I have a BOV that is plumbed to recirculate back between the MAF and turbo at the stock inlet.

I do have a AEM wideband but I have not connected it to Nistune yet. After I let off the throttle my AFRs go lean and the car dies. Car idles at around 14.1-14.5 AFR.

Any thoughts would be appreciated.

[Matt]

Difficult to see what is going on in those logs. If you can get the UEGO wired into Nistune and then we can see the AFRs against the other parameters

[Rob280z]

OK I should get the wideband connected to Nistune here in a few days.
What parameters would be helpful for a log? TPS, RPM, AFR what should I add?

Sorry never done this before.

Thank you for your help

[Matt]

That ECU will automatically log all parameters, just need AFR in there from the UEGO

[bachig24u]

Often the TP Max is too high, the fuel map under light load is too high, the Decel spark is not high enough or DFCO needs to be a little wider.

The problem can be worse with a BOV, MAF, Injector upgrades and FPCM elimination

[mtnickel]

To add to this discussion,
For cars without a speed control, the cut/recover is a bit wonky. When rolling to a stop while on DECEL and engine braking, the ECU is expecting the revs to drop a lot faster since it thinks the car is speed 0 or in neutral. It in turn adjusts the Idle valve to keep cutting out air to try to drop the idle. When you finally come to a stop, the engine wants to stall because it's completely closed the idle valve and it's now quickly trying to open.

To combat this, you can open your stock idle screw on your idle valve (it's a flat head screw on the valve i believe). The bogging is not always attributed to poor AFR but can be from just not enough air as well.

I plan to wire in a GPS speed sensor to improve driveability (as well as hopefully use launch control).

Regards,
mark