Part throttle issue

Nixlimited · 07-23-2006, 07:38 PM

So my cars runs brilliantly with the exception of one area - I have an issue with very low throttle application in OLF while cruising. The symptoms are jerkiness of the car when just trying to maintain a speed and - thanks to my new Innovative Lamda guage - an AFR that is bouncing all over the place (like from 11:1 - 16:1). It happens in all gears at very low loads, but is much easier to tell in gears 1-3. My guess is that the short term fuel trim is going nuts there, but I am not sure how to fix it...

Also, how are you all plugging in your cobb AP cable and AFR cable at the same time? Both run on serial connections of which my laptop has 1.

pt518sti · 07-23-2006, 08:31 PM

welcome to the club

overdose · 07-24-2006, 02:53 AM

Quote:

Originally Posted by Nixlimited

So my cars runs brilliantly with the exception of one area - I have an issue with very low throttle application in OLF while cruising. The symptoms are jerkiness of the car when just trying to maintain a speed and - thanks to my new Innovative Lamda guage - an AFR that is bouncing all over the place (like from 11:1 - 16:1). It happens in all gears at very low loads, but is much easier to tell in gears 1-3. My guess is that the short term fuel trim is going nuts there, but I am not sure how to fix it...

Also, how are you all plugging in your cobb AP cable and AFR cable at the same time? Both run on serial connections of which my laptop has 1.

Log the fuel trims/timing/afr in the trouble spot, to run 2 serial devices get a usb-to-serial adapter available just about anywhere that sells computer stuff, or online

pt518sti · 07-24-2006, 07:37 AM

Mine was related to the throttle plate position..
Because our cars are drive-by-wire, there can be spots where the throttle plate makes drastic movements even though very little throttle has actually been given.
Mine was very bad after my initial 20g tune and I brought it back to the tuner thinking it was a A/F ratio issue, but he ended up finding that A/F was spot on and it was the throttle plate position that was causing the car to be very jerky under light throttle.
The tuner was able to smooth it out quite a bit and the car is a lot nicer just cruising around. It still isn't as smooth as stock or even a stage 2 protune, but it's a lot better.
If your car is a daily driver an issue like this can make driving around town a miserable experience.. believe me, I know.

I bet you have the same issue.. good luck getting it straightened out

Nixlimited · 07-24-2006, 08:04 AM

Quote:

Originally Posted by pt518sti

Mine was related to the throttle plate position..
Because our cars are drive-by-wire, there can be spots where the throttle plate makes drastic movements even though very little throttle has actually been given.
Mine was very bad after my initial 20g tune and I brought it back to the tuner thinking it was a A/F ratio issue, but he ended up finding that A/F was spot on and it was the throttle plate position that was causing the car to be very jerky under light throttle.
The tuner was able to smooth it out quite a bit and the car is a lot nicer just cruising around. It still isn't as smooth as stock or even a stage 2 protune, but it's a lot better.
If your car is a daily driver an issue like this can make driving around town a miserable experience.. believe me, I know.

I bet you have the same issue.. good luck getting it straightened out

Yes, abrupt throttle plate movement would certainly cause the AFRs to move all over the place at a rather low resolution point on the MAF.

I wonder if Wolfplayer ever posted anything more on his throttle mapping...

STirish · 07-24-2006, 07:30 PM

Quote:

Originally Posted by Nixlimited

So my cars runs brilliantly with the exception of one area - I have an issue with very low throttle application in OLF while cruising. The symptoms are jerkiness of the car when just trying to maintain a speed and - thanks to my new Innovative Lamda guage - an AFR that is bouncing all over the place (like from 11:1 - 16:1). It happens in all gears at very low loads, but is much easier to tell in gears 1-3. My guess is that the short term fuel trim is going nuts there, but I am not sure how to fix it...

Also, how are you all plugging in your cobb AP cable and AFR cable at the same time? Both run on serial connections of which my laptop has 1.

This will happen with larger injectors at low load. I can get it to happen with my 740cc injectors, your 850s will be worse.

Nixlimited · 07-25-2006, 12:51 PM

May have identified a candidate cause - the PCV valve leaking air post MAF. Gonna do some research.

jays05 · 07-25-2006, 03:27 PM

I get the same light throttle jerkiness with my PE850's. It's been that way ever since I put the injectors in the car, even back when I was on the stock turbo. I'll give the new drive by wire maps a try, but I have a feeling this has more to do with the larger injectors.

This is the only remaining oddity in my street tune, I'm glad to see I am not alone.

Side note, I have been considering ditching my pcv valve all together, have you considered this?

WolfPlayer · 07-26-2006, 04:51 AM

It's the injectors. Welcome to the club.

My JECS injectors do the same thing but it is nothing big or violent on my setup. It rarely does it. I only notice it when going down a hill at the most minute throttle position (very low load which means incredibly low IPWs). In my case it has nothing to do with the throttle plates. It is the injectors. You guys with 850cc injectors are going to have it worse. The injector pulse width is just too damn low. There is nothing that can be done about it right now until somebody disassembles the Subaru code and tracks IPW information. There MIGHT be a minimum IPW barrier set as a constant on the ECU that could help. However, nobody has went that far into the ECU code yet (that I know of at least).

I can totally get rid of this weird phenomena if I richen up the fuel map at that position by about 0.7 AFR points. At that point, everything will be 100% rock solid. This proves it is a fueling issue (for me). The AFRs then become stable on the wideband ... wherease before, they were bouncing around.

I am working on a new version of the TDC changes that is even better. It won't help anything with regard to this thread. However, I wanted to mention it since others have been talking about it. I need to make a couple more base flashes before I release it. This won't be a big change from the last one because the last one did a really good job. But, it will be better.

t

cnstman · 07-26-2006, 09:30 AM

Quote:

Originally Posted by Nixlimited

May have identified a candidate cause - the PCV valve leaking air post MAF. Gonna do some research.

any word on this?

Nixlimited · 07-26-2006, 09:41 AM

Quote:

Originally Posted by cnstman

any word on this?

I had a long discussion with Jeff @ Perrin yesterday and I am damn near positive this is contributing to my issues based on my new understanding of the PCV routing. Basically, my car is currently setup where the intake manifold will pull vacuum through the catch can which gets free unmetered air from the pre-turbo intake. Recall that I am blowthrough so my MAF is way down the line right before the throttle body. This would explain the main symptoms of my problem which are 100% correlated with how much vacuum I am pulling. As soon as the car is under any load (i.e. very little vacuum), there is no issue. The problem is, I am getting ready to move and my cars are getting shipped so I have no time to play with it in the next 2 weeks. For the time being I have parked the STi and am driving the M.

I do believe that Wolfplayer is right about the big injectors, but what I am dealing with is way to severe to be just that.

WolfPlayer · 07-27-2006, 05:04 AM

It's the injectors. No matter what you do, you are going to end up with some slight hesitation at very light load on warmer days. The injectors just can't fire reliably at that IPW.

All the posts on the boards everywhere lead people to believe that you can put in bigger injectors and it will run like stock with no oddities. This is 100% not true - unless you live in a cold climate and don't see stop and go traffic much.

t

pt518sti · 07-27-2006, 06:29 AM

I was under the impression the only thing that would be effected was the idle, so it came as a surprise to find out that my car would no longer be as smooth as it used to be

I did have my tuner mess with it until it was as smooth as possible and it really isn't all that bad now, but like I said, it's definitly nowhere as smooth as my stage 2 Protune.

WolfPlayer · 07-27-2006, 06:39 AM

Quote:

Originally Posted by pt518sti

I was under the impression the only thing that would be effected was the idle, so it came as a surprise to find out that my car would no longer be as smooth as it used to be

I did have my tuner mess with it until it was as smooth as possible and it really isn't all that bad now, but like I said, it's definitly nowhere as smooth as my stage 2 Protune.

Mine is totally smooth except for 2 things ...

1) Idle while the car is stopped on a hot day. The intake temps get up high. Less fuel is needed. The commanded IPW is lower. Reaches the lower boundary of an acceptable, reliable, smooth IPW.

2) Going down a hill at extremely light loads. The grade of the hill matters. It doesn't do it all the time. Usually only on a hot day.

Overall, I consider my car really smooth and runs very close to stock. Some people can't even tell that it has bigger injectors installed. I am just anal. I can't imagine running the 850s though.

t

pt518sti · 07-27-2006, 06:42 AM

Quote:

Originally Posted by WolfPlayer

Mine is totally smooth except for 2 things ...

1) Idle while the car is stopped on a hot day. The intake temps get up high. Less fuel is needed. The commanded IPW is lower. Reaches the lower boundary of an acceptable, reliable, smooth IPW.

2) Going down a hill at extremely light loads. The grade of the hill matters. It doesn't do it all the time. Usually only on a hot day.

Overall, I consider my car really smooth and runs very close to stock. Some people can't even tell that it has bigger injectors installed. I am just anal. I can't imagine running the 850s though.

t

I have the Perrin modified stockers.
If you're running the Nismo 720's or whatever they are probably much better.

07-23-2006, 07:38 PM	#1
Nixlimited Professional STI Racer Car: 05 STi CGM Fav Mod: Tuning... Location: San Diego Posts: 811 Join Date: Feb 2005 Trader Rating: (0)	Part throttle issue So my cars runs brilliantly with the exception of one area - I have an issue with very low throttle application in OLF while cruising. The symptoms are jerkiness of the car when just trying to maintain a speed and - thanks to my new Innovative Lamda guage - an AFR that is bouncing all over the place (like from 11:1 - 16:1). It happens in all gears at very low loads, but is much easier to tell in gears 1-3. My guess is that the short term fuel trim is going nuts there, but I am not sure how to fix it... Also, how are you all plugging in your cobb AP cable and AFR cable at the same time? Both run on serial connections of which my laptop has 1. This ad is not endorsed by this member. Please register or login to hide this ad.

07-23-2006, 08:31 PM	#2
pt518sti S204 Racer Car: 2005 White/Gold STi Fav Mod: TD06-20G/Tein Flex coilovers Location: New York Posts: 2,909 Join Date: May 2005 Trader Rating: (8)	welcome to the club

07-24-2006, 07:37 AM	#4
pt518sti S204 Racer Car: 2005 White/Gold STi Fav Mod: TD06-20G/Tein Flex coilovers Location: New York Posts: 2,909 Join Date: May 2005 Trader Rating: (8)	Mine was related to the throttle plate position.. Because our cars are drive-by-wire, there can be spots where the throttle plate makes drastic movements even though very little throttle has actually been given. Mine was very bad after my initial 20g tune and I brought it back to the tuner thinking it was a A/F ratio issue, but he ended up finding that A/F was spot on and it was the throttle plate position that was causing the car to be very jerky under light throttle. The tuner was able to smooth it out quite a bit and the car is a lot nicer just cruising around. It still isn't as smooth as stock or even a stage 2 protune, but it's a lot better. If your car is a daily driver an issue like this can make driving around town a miserable experience.. believe me, I know. I bet you have the same issue.. good luck getting it straightened out

07-25-2006, 12:51 PM	#7
Nixlimited Professional STI Racer Car: 05 STi CGM Fav Mod: Tuning... Location: San Diego Posts: 811 Join Date: Feb 2005 Trader Rating: (0)	May have identified a candidate cause - the PCV valve leaking air post MAF. Gonna do some research.

07-25-2006, 03:27 PM	#8
jays05 Spec C Club Fav Mod: when it's not blown up Location: Upstate NY Posts: 1,591 Join Date: Nov 2004 Trader Rating: (0)	I get the same light throttle jerkiness with my PE850's. It's been that way ever since I put the injectors in the car, even back when I was on the stock turbo. I'll give the new drive by wire maps a try, but I have a feeling this has more to do with the larger injectors. This is the only remaining oddity in my street tune, I'm glad to see I am not alone. Side note, I have been considering ditching my pcv valve all together, have you considered this?

07-26-2006, 04:51 AM	#9
WolfPlayer Moderator & ECU Tech Car: 05 CGM STI Fav Mod: mo boostaz Location: Fredneck, MD Posts: 3,639 Join Date: Jun 2004 Trader Rating: (6)	It's the injectors. Welcome to the club. My JECS injectors do the same thing but it is nothing big or violent on my setup. It rarely does it. I only notice it when going down a hill at the most minute throttle position (very low load which means incredibly low IPWs). In my case it has nothing to do with the throttle plates. It is the injectors. You guys with 850cc injectors are going to have it worse. The injector pulse width is just too damn low. There is nothing that can be done about it right now until somebody disassembles the Subaru code and tracks IPW information. There MIGHT be a minimum IPW barrier set as a constant on the ECU that could help. However, nobody has went that far into the ECU code yet (that I know of at least). I can totally get rid of this weird phenomena if I richen up the fuel map at that position by about 0.7 AFR points. At that point, everything will be 100% rock solid. This proves it is a fueling issue (for me). The AFRs then become stable on the wideband ... wherease before, they were bouncing around. I am working on a new version of the TDC changes that is even better. It won't help anything with regard to this thread. However, I wanted to mention it since others have been talking about it. I need to make a couple more base flashes before I release it. This won't be a big change from the last one because the last one did a really good job. But, it will be better. t

07-27-2006, 05:04 AM	#12
WolfPlayer Moderator & ECU Tech Car: 05 CGM STI Fav Mod: mo boostaz Location: Fredneck, MD Posts: 3,639 Join Date: Jun 2004 Trader Rating: (6)	It's the injectors. No matter what you do, you are going to end up with some slight hesitation at very light load on warmer days. The injectors just can't fire reliably at that IPW. All the posts on the boards everywhere lead people to believe that you can put in bigger injectors and it will run like stock with no oddities. This is 100% not true - unless you live in a cold climate and don't see stop and go traffic much. t

07-27-2006, 06:29 AM	#13
pt518sti S204 Racer Car: 2005 White/Gold STi Fav Mod: TD06-20G/Tein Flex coilovers Location: New York Posts: 2,909 Join Date: May 2005 Trader Rating: (8)	I was under the impression the only thing that would be effected was the idle, so it came as a surprise to find out that my car would no longer be as smooth as it used to be I did have my tuner mess with it until it was as smooth as possible and it really isn't all that bad now, but like I said, it's definitly nowhere as smooth as my stage 2 Protune.