Post tip-in lean

[tazgn]

I've been trying to figure out how to fix this and haven't, so I'm turning to the geniuses on here for some help. When I accelerate rather slowly (everyday driving stuff) and push the accelerator to say 1/4 throttle and hold it, the A/F initially works as expected (slightly richens as AE fuel dumps in). BUT, then it goes max lean (15.94) for a while immediately afterwards and the car will spit and sputter. This last for about 4 seconds and the car will recover and take off normally. HOW do I get rid of this post tip-in lean condition????

Thanks,
Derrick

 

[Eric Stage I]

I would probably log the occurence as it happens, then look to see where in the VE table it is happening. Then, raise the VE numbers where it occurs to get the a/f ratio where it should be. If you want, make the log file available and maybe some of the guys around here will look at it for you.

Regards,
Eric

 

[tazgn]

I'll send the log file to anyone that wants to see them. I played with the VE tables, but it's just a transient lean problem. When steady state cruising in those areas of the VE table, it's pretty good (<5% correction). It just seems like it goes lean when recovering from the AE fuel for a few seconds. And only at part throttle light acceleration conditions. Pretty damn annoying and embarrassing having people watch the car as I pull away then having it stumble and pop until this problem goes away after a few seconds....

Derrick

 

[Eric Stage I]

Maybe you could work it out with the MAP AE. There is a decay setting for how fast the AE fuel is removed. Maybe you're decaying too fast.

I'll be happy to look at it. Send the .gct and log file to eric@turbotweak.com .

Regards,
Eric

 

[S351 R]

Well Im definitely new to FAST.... but my car did similarly with the calibration that came with the ecu. Something that helped immediately was lowering the AE MAP decay from 2040 to 540. I still see rich-to-lean spikes (or sometimes vice versa) on gear shifts or on/off throttle but drivebility is much improved.

How is your extended decel/down shifting with closed loop on? Lots of excessive fuel as O2's correct for the usual 15.94 readings?

 

[dhegge]

I too have the exact same Lean tip-in problem. I was told at one point that large TB's could cause that to occur. I don't know for sure but I sure would like to know. Mine goes dead lean at tip-in and then corrects and then stabilizes. It does cause a bit of a miss if you jump in real hard. I have "Learned" to drive around the problem. I would love to find a solution to this problem. Please keep us in the loop on any progress that you might make and I will do the same.

Doug

 

[tazgn]

This damn thing has me at my wits end now!!!! I've tried everything I can think of to try and stop the lean condition. Under very light throttle the A/F will dip down (assume due to AE fuel) then swing way up to 15.91 (max of the O2 sensor). I've tried the MAP AE decay rates from 2 to 2000 with the same results (although it was much worse with larger decay rate numbers). I've added and removed AE fuel from TPS AND MAP. My MAP AE settings are 110 for the limit and 8 for the threshold.

I've tried playing with the closed loop correction limits too. 50% for the closed loop gain (won't let me go higher), and 10 for the step % (won't let me go higher).

H E L P !!!!!

Derrick

 

[Craig Smith]

3 things. First, is it causing a problem in how it runs, or is it just a freaky looking thing on a data log? The only thing to be concerned with is how it responds. If it acts sluggish or won't rev well, we have a problem. If you are simply trying to stabilize an a/f ratio while revving the engine, you are going to be all the way at your wits' end soon, cuz it ain't gonna happen. All you need to happen with this stuff is to get it to respond well to the throttle. I did read your earlier posts and I know that there has been a drivability problem as a result of this; is this still the case?

Second, describe for me how the AE Fuel vs. TPS Position graph is set up. Also, what size injectors do you run?

Third, unless you have a very noisy MAP signal at idle, you can probably cut your MAP noise threshold in half. 8 really is a lot.

 

[TurboTR]

>I too have the exact same Lean tip-in problem. I was told at one point that large TB's could cause that to occur.

It's just the nature of the beast. In general a tip in tends to cause a lean spike, a tip out a rich spike. That's why carbs had accelerator pumps, and EFI has the analog in transient AE fueling.

>I don't know for sure but I sure would like to know. Mine goes dead lean at tip-in and then corrects and then stabilizes. It does cause a bit of a miss if you jump in real hard. I have "Learned" to drive around the problem. I would love to find a solution to this problem.

Well first the VE table has to be correct in a steady state sense in *all* cells that the operating point moves through during a tip in event. With the wb O2 FAST this is pretty easy and quick to achieve. Then it's just a matter of getting the AE fueling right. IMO the AE vs delta TPS is sufficient to fix the tip in issue in most cases. In fact trying to mess with 2 AE systems is probably too many variables and not even necessary IMO and IME. I generally just zero out the AE vs delta MAP.

JMO.

TurboTR

 

[tazgn]

Yep, this does cause a driveability problem. When lightly accelerating from say a stop sign, the car will start to take off, then drop dead on it's face for a couple seconds and then take off again and be fine. The A/F goes up to >15.91 when it goes dead. But when I step on the throttle initially the A/F will drop to the 10's (assuming due to AE fuel as expected). O2 corrections are trying to do the right thing (slightly negative when the AE fuel causes A/F to drop initially, then max out at 25 when A/F goes way lean until A/F turns back to where it should be).

My AE vs TPS amd AE vs MAP maps are very similar in shape, the MAP is just slightly lower pulse widths. It goes from 0/0 to about .4 at the first step of the chart, then levels off to about 1.4 at the last step of the chart (bottom axis). Does the MAP AE decay value affect the TPS AND MAP AE fuels or just the MAP AE fuel???

Oh, I'm running 83# injectors and a 70mm thottle body. I'm going to screw with it a little more today. I'm going to try things like the IAC throttle follower. I'm going to make the IAC open later with TPS position. This stumble doesn't happen when I mash the pedal greater than about half way.

Derrick

 

[tazgn]

I just added a link to my web page where you can download my current GCT file to look at as well. For some reason it doesn't download with the new netscape, but works fine with internet explorer... I'm NO webpage expert....

Derrick

 

[TurboJim]

My car did this when I had closed loop coming in at 1500 rpm. SLightly ease on the gas and it'd sag. Just like you, would go to 15.94 or something AF. I just couldnt get the 2 VE cells right. One number was too high, lower it one number and it was too low. I needed something in between.I I got tired of ****ing with it and I lowered closed loop enable RPM and its fixed Yes, correction goes to like +10%, but it doesnt stumble anymore. I had thought of redoing the whole VE table in 400rpm scale (its at 500 now), but dont know if that will help me or not.

Cars been in the garage since like September... with the new baby I have absolutely ZERO time for the car.

 

[Craig Smith]

Jim, congrats on the new baby!

You know what I have seen cause this problem? Throttle blade adjustment. I have seen situations where the IAC was open so far at idle that when you tipped the throttle open and exceeded the Max TPS for Idle, the IAC would drop down to the throttle follower setting. The increase in throttle angle was insufficient to supply the amount of air being provided by the IAC motor while idling in these situations, and it had the same effect as putting your hand over the throttle body. Even though one might think this would cause the engine to get very rich, it basically shuts off the air supply to the engine and the WBO2 will go lean. At least that's what I have seen happen.

Is this possibly kicking your butt?

 

[TurboJim]

I dont recall how far IAC was open, but I will give it a look-see when I move my snowplow out of in front of the garage (so I can take the car for a spin)