Tephra v7 9653 thottle hang

[simple_lancer]

I've tried making the 60 and 70 load cells in the Decel Fuel Cut Delay tables a lot lower. Seems to help, the default value is 61, I've tried 20 and it seems to crackle and pop a lot less when I lift off.

So can people confirm that zeroing the two tables I mentioned helps with throttle hang?

I think the finishing touch is to reduce the decel fuel cut delay tables and we should have the problem solved!

[logic]

Originally Posted by Jack_of_Trades

Does anyone know a way to activate Evoscan's SAS Mode to adjust the BISS while being able to still log RPM???

Yes. Enter custom request "C3" at the bottom of the window, which should return a response of "FF". At that point, you should be in SAS mode, but still logging whatever it is you want logged. As an added bonus, it won't disable until you either stop logging, or send a custom request of "F3" to clear it.

[simple_lancer]

I've tried making the 60 and 70 load cells in the Decel Fuel Cut Delay tables a lot lower. Seems to help, the default value is 61, I've tried 20 and it seems to crackle and pop a lot less when I lift off.

So can people confirm that zeroing the two tables I mentioned helps with throttle hang?

I think the finishing touch is to reduce the decel fuel cut delay tables and we should have the problem solved!

[jrohner]

If you're having the issue, why not unplug the ISC and see if it acts the same? Why wouldn't that be a super easy way to tell? Heck, my 1G DSM runs and idles great and consistent with the ISC unplugged (I'll probably always leave it unplugged), even @ cold startup in the winter.

Yes, changing the decel fuel cut would help (RPMs would have to drop if there's no fuel), but that still has nothing to do with the cause. You probably don't want it to cut fuel instantly anyways, as having fuel for a second after a WOT should cool things down some.

Here are the only things that I think could contribute to and compound the issue: ISC, AFR, timing, vacuum leak, a real physical throttle hang such as the throttle plate or cable. Also, I would think the BOV could have an effect on this -- if the BOV doesn't open, open enough, or flow enough, the boost pressure could be high enough that it pushed a large enough volume of air through to cause the RPMs to not drop right away when the throttle is closed.


I personally only noticed a problem when I was running speed density (I've noticed it on other vehicles too, I once drove a 93 Mustang that did it really bad making it hard to even shift smooth). Now when I'm back using the MAS, the RPMs actually drop too fast when the engine is cold.

I'm on v7t5 of 96530706, btw

[jba3]

Bump for good info

[donour]

This is slightly off topic, but has anyone looked into the enrichment that happens on throttle lift?

This is probably causing a big drop in mileage for me. Feathering the throttle results in a mixtures bouncing between stoich and rich rather than stoich and lean like you want.

d

[Slo_crx1]

Oddly enough this is not one of the issues I've noticed with the new v7 patch on my '03. It could partly be because I'm on SD now, but I even tried running the MAF version first and never had this problem.

[donour]

Originally Posted by Slo_crx1

Oddly enough this is not one of the issues I've noticed with the new v7 patch on my '03. It could partly be because I'm on SD now, but I even tried running the MAF version first and never had this problem.

As simple_lancer suggested, I lower the decel fuel tables _significantly_ and that seemed to help although it still dips richer than I would think is necessary.

d

[Slo_crx1]

Originally Posted by donour

This is slightly off topic, but has anyone looked into the enrichment that happens on throttle lift?

This is probably causing a big drop in mileage for me. Feathering the throttle results in a mixtures bouncing between stoich and rich rather than stoich and lean like you want.

d

Actually I may have stumbled across something regarding that when playing around with my SD tune today. As far as I can see, adjusting the incorrectly labeled "accel enrichment" table seems to lean out the throttle lift. Whenever I adjusted the values higher, it seemed to lean out more and more. You can give that a try too and see if that's possibly what it's for.

[donour]

Originally Posted by Slo_crx1

Actually I may have stumbled across something regarding that when playing around with my SD tune today. As far as I can see, adjusting the incorrectly labeled "accel enrichment" table seems to lean out the throttle lift. Whenever I adjusted the values higher, it seemed to lean out more and more. You can give that a try too and see if that's possibly what it's for.

I'm not sure that's really the table to be changing. The values in my original rom (96420008) are almost the same and it doesn't have the problem.

d

[Slo_crx1]

Originally Posted by donour

I'm not sure that's really the table to be changing. The values in my original rom (96420008) are almost the same and it doesn't have the problem.

d

I would say then look more towards the scaling of the MAF and the latency/size of the injectors then compared to the o2 and LTFT feedbacks. Feathering the throttle would usually put it in the control of closed loop anyway.

[donour]

Originally Posted by Slo_crx1

I would say then look more towards the scaling of the MAF and the latency/size of the injectors then compared to the o2 and LTFT feedbacks. Feathering the throttle would usually put it in the control of closed loop anyway.

This is basically a stock car. The fuel trims seems to be OK. All this happens while in closed loop. I cruise along, fuel trims are right at 14.7. A lift (like going down a gentle hill) causes a AFRs to dip down to low 11s when they should go lean very quickly.

d

[Routybouty]

Originally Posted by simple_lancer

- ISCV Demand RPM Adder [rpm > 4500, load > 170, speed > 12 mph]
- ISCV Demand RPM Adder (Moderated by Baro, IATS) (FFFF6EA8) (sub_204B6) [sub_1EFC0]

These two tables add up to 100% on top of your idle demand percentage and makes the lookup value much higher in the idle stepper lookup table.

Zero these two tables out, and log your iscv steps in evoscan.

I have had no throttle hang after this. It's the only thing I changed; all stepper tables and ISCV tables are stock. I used to be able to induce hang by giving about 75% throttle up to 4k-5k rpm and then letting off. Now it's gone woot!

[Slo_crx1]

Originally Posted by donour

This is basically a stock car. The fuel trims seems to be OK. All this happens while in closed loop. I cruise along, fuel trims are right at 14.7. A lift (like going down a gentle hill) causes a AFRs to dip down to low 11s when they should go lean very quickly.

d

I did have a case like that previously on my old 94170015 rom. Usually after light acceleration and lightly letting off the throttle my afr's would creep down to the low 11's/high 10's range. In the end it turned out my throttle cable was just a hair too tight (even though it seemed like there was enough slack), and after adjusting it out I never had any throttle hang issues since then.

Lately however with the temperature dropping, I have noticed slight throttle hang even after it seems to come up to temp. Usually it's pretty brief, lasting maybe about 2-3 seconds and then drops. If I drive for any longer periods of time, there usually isn't any hang at all during that time so it may be that I'm not fully up to temp yet.

[Evo_Kid]

Originally Posted by simple_lancer

Don't fiddle with the Idle stepper lookup table.
It just makes the rev hang happen at a lower rpm, but it still persists.

The reason why there is rev hang, is there is a table that adds a LOT to your idle demand (the vertical axis on the idle stepper lookup table) and causes the stepper position to go really high.

The tables I used to completely erradicate throttle hang were under the "ISCV Control" category:

- ISCV Demand RPM Adder [rpm > 4500, load > 170, speed > 12 mph]
- ISCV Demand RPM Adder (Moderated by Baro, IATS) (FFFF6EA8) (sub_204B6) [sub_1EFC0]

These two tables add up to 100% on top of your idle demand percentage and makes the lookup value much higher in the idle stepper lookup table.

Zero these two tables out, and log your iscv steps in evoscan.
You'll notice instead of going up to 120 or so when you accelerate hard, the iscv steps will only go up to around 70 instead, which will not induce rev hang. The iscv steps will also decay very quickly, since it won't reach such a high value like before. I haven't noticed any reduction in idle quality or part throttle driveability.

You may have to play with your Decel Fuel Cut Delay tables as well, but I don't know what the difference is between tables 1, 2, 3, and 4 are. I just made all my tables the same values as the ones in table 2 (this one has the lowest values and is the same as table 4).

Sorry for the long explanation, but it kind of makes it hard without pictures!

This post has a wealth of info on how the idle speed control system works.
ISCV control system disassembly

Go MrFred you are a legend!

So do more people have updates? Does this seem to be the correct fix. If its tested to be the complete fix, then it should be stickied