CA18DET deceleration issues

[mattlovo]

Hey Matt and whoever is reading this, after much reading on engines and fuel cut, I realise the dragging issue in deceleration was caused by insufficient fuel.
So I tried to raise the TP min while decelerating downhill as suggested by a fellow Nistune user Louis
Got the higher end of the rpm range sorted out and it is better now.

However, I am unable to solve the 800 - 1200 rpm where the idles at with perfect AFRs 14.7-15.0.

If I raise TP min, it gets too rich for that range.
If I don't, the engine drags itself to a slow in high vacuum (AFR 22.2) before it jerks back at 1000rpm where the idle takes over and the ecu resumes fuel injection (AFR goes back to 14.7).
If I cut injector timing, I probably screw up the whole map...

As for the rest of the map, AFRs are all good when boosting and cruising.

Will appreciate anyone's inputs on this.

[Matt]

What about increasing latency, or increasing the values in that area of the VQ map directly? TP min is effectively a clamp on minimum load

[mattlovo]

Now I am aware that the fueling on these things has a fuel cut when the engine is decelerating with no throttle input. I have read that the fueling comes back in at 900 RPM.

That seems awfully low.
I dont know if that value is accurate.
If I can adjust this value there is a pretty good chance I could help the engine to catch itself and not stall. I cannot however find an adjustment in Nistune, or is this buried in the coding and not adjustable? (something like an overrun table?)

[Matt]

Fuel cut / recovery is between 1200rpm and 1100rpm at 80 degC. Not sure where you read at 900rpm?

[mattlovo]

Thanks Matt. There seems to be no way to change the settings on this too despite playing around with the Fuel Cut/ Fuel Recovery tables.

[mattlovo]

Hi guys, is there a table that I can use in the Type 1 ECU to adjust the speed at which the engine decelerates?

I notice there is an idle/deceleration timing table but I am not sure if it will work when the TPS is ON.
Would increasing deceleration timing per cell increase the engine brake?

I tried to do that, and the end result was resuming throttle would be jerky. I presume is due to too big a timing difference when accelerating.

[Matt]

There is no table for that in the ECU

[mattlovo]

Alright...

How about the Idle/Deceleration tables?
Would it make a difference if I advance or retard the timing values?

[Matt]

Timing does not affect fueling

You need to go back and look at your MAF, resulting TP (load) and injection time and see where it is overfueling and why

If you still have high MAF readings on low RPM, then it will consequently inject more fuel. I can only give general advice however without directly working on the vehcile

[mattlovo]

Thanks Matt, really appreciate your time to be on the forum and replying to us.

I am still struggling with finding a way to get the ecu to resume fueling or to catch the idle drop off throttle earlier due to the lighten flywheel which makes revs drop fast. Acceleration is fine.

Increasing min tp load just messes up the AFR at cruise.

As there isn't a way to get the ecu to resume fueling earlier instead of Fuel cut / recovery, between 1200rpm and 1100rpm, I cant seem to smoothen out the drive.

[raddy]

well, try to move tps to get idle switch close earlier to activate aac valve soon enough to avoid rpm drop...

[Matt]

Post a screenshot of your AFR trace (AFR vs RPM/TP) and also the injection time trace, and also MAF trace. It may give you a clue (or post log file and tune file)

[mattlovo]

Hi Matt, haven't gotten the new AFR gauge linked up to the nistune yet. Will work on this soon.

I have been trying to adjust the injector latency slightly more to see if it helps with the issue.

Seems like the load off throttle when the car is decelerating is too light, jerks when it resumes fueling at 900rpm (think that was the factory setting if I am not wrong).

Min TP has been raised quite abit. Anymore and cruising AFR will be a mess.
I also put the stock flywheel back in...seems abit better to drive but the issue still persist

[Matt]

Yeah increasing TP min is not normally done, if you are adjusting TIM and latency, so raising it too much will increase the minimum amount of TP (and injection)

[mattlovo]

If I were to raise my Injector Latency from 880ms to 900ms, would that affect the fueling tables? Or just at idle?
I have tried to play around and raised it to 950, but it idled way too rich.


Map is pretty much solid except for the lack of deceleration load which I am trying to solve.
TIM, I guess will scale the fuel tables if I were to try and change it.