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Stumble with cruise control


fishbone

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*sigh*

 

I'm just gonna start with the burning question first and then leave it open and see where it goes.

 

What values are normal to be observed in A/F Correction #1, if any?

I've looked far and wide on the internets and wasn't able to get a straight answer.

 

What I am seeing: sharp and rapid oscillation at steady throttle between the range of +-10%, with occasional spikes in the deep end of 19% or more

What I am feeling: stumble, but only with cruise control engaged

What I have done: cleaned the **** out of the MAF, replaced front O2 sensor with brand new OEM one, checked for disconnected/damaged/cracked hoses, etc.

 

Car: 2005 legacy auto, 110K miles, typical stage 2

Not sure how long I've had this issue, whatever it is, going on since I've only recently used cruise control for the first time but I can tell you it was working fine as of 8 months ago or so and it has not been touched mechanically speaking in any way.

 

 

Ongoing threads regarding the mechanical side, I hate to cross post but I am not getting a lot of input on the datalogging side. Maybe I'm just being impatient. I'm looking for direction at what to look to see what the car is telling me might be wrong.

The car drives fine but there's something that it doesn't like recently which

 

For reference:

http://legacygt.com/forums/showthread.php/stumble-cruise-only-218669.html

http://legacygt.com/forums/showthread.php/oscillating-cruise-control-219862.html

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I do remember a comment a friend of mine who is a tuner made about a couple years ago while he was riding shotgun and datalogging the car. He noted that my MAF readings were a bit too jumpy at cruise and idle.

 

LV would be largely meaningless at this time since I had reset the ECU just this AM after I replaced the front O2 sensor.

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Based on the airflow ranges above, can anyone tell me what the likely culprit might be of the leak? Why would cell B have a lower enrichment than C? I would expect the higher you go the enrichment would be linear?

I am confused as to how that leak appears to be there at low airflow and yet my idle speed is rock solid and the car feels absolutely fine in every respect.

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I feel ya man. chased ghosts for months before I figured my weird leak/knock situation out.

 

Positive trims are usually vac leaks right?

I'd be looking at the inlet. Have you closely inspected that or boost tested it?

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No and no. I did a visual inspection and saw nothing, but I am not 100% on the underside of it. So it's time to whip out the carb cleaner and go to town.

I have seen new spray patterns under the hood in areas that I have not seen before.

For example, right where the intercooler couples to the TB hose, it looks wet with oil. Right behind it, on the firewall and a couple other areas there are oily spray/splatter patterns. So it looks like I will be taking especially close look to that area. I wrestled with the TMIC just a couple weeks ago and everything seemed nice and tight, no visible tears. Then again at that time I did not put anything under the scope since I was assuming the O2 was at fault. The car has 100K miles so it is time I replace the PCV valve.

 

Again ... car runs great in every other respect. Hits target boost and hits it fast, idles rock solid, no CEL yet, etc etc. The only thing that tipped me to an issue was the stumbling/stuttering cruise control.

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Mine inlet was ripped right at the turbo, couldn't tell until I had the band clamp totally off. I also couldn't get idle to change with carb cleaner or starting fluid. But it was definitely leaking.

 

Definitely replace the PCV, and check the TB/TMIC at the TB side. That's where mine was getting all funky.

 

I was having a very similar situation. first with a torn turbo inlet, then with the new inlet slipping off the turbo ever so slightly over time.

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Had the TMIC off today and spotted a couple things. First, the BPV gasket seemed to have a leak because there was an area of the stock rubber gasket that was a bit dirty and had a bit of oil on it. Then the TB hose appeared to be loose on both sides and was spraying oil out under boost, splatered on the firewall. Cleaned all contact areas thoroughly and made sure everything was nice and tight.

 

Unfortunately, the issue is still there. It seems more precise though, meaning that the AF Learning 1 immediately goes to 10% and stays there at idle. At part throttle it stays around 3.5 to 5% or so. Either way, I swear I looked closely at all the hoses and saw nothing, so at this point I am suspecting a gasket leak somewhere. Every time I had a hose pop off or something like that the amount of enrichment went to max and threw a CEL. Right now it's not going over ~10%.

Gonna call a nearby shop and do the smoke test and see what happens.

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I hope it's not the turbo inlet as I really don't want to have to pull the IM off. I had TGV deletes done two years ago and at that time the guy that worked on the car told me the inlet looked great so there was no apparent need to replace it. I kinda regret I didn't do it anyway.

I'm hoping it's the TB hose or something easy like that.

 

Cylinder 1 registered 2 roughness events but that was only with cruise control on and sputtering around. Not ready to rule out injector/fueling issues but at this point everything seems to point to a vacuum leak.

 

What is vacuum supposed to register with the car out of gear, idling? I'm at about 600 feet elevation. In Nebraska I was at about 1200 and I think it was reading -10PSI or so?

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Went to the shop today, hooked up the smoke machine right in the IM, smoke only came out at the intake, no evidence of leaks anywhere. Given the fact that the A/F Correction and Learning is actually inconsistent, I think this is more symptomatic of the tune needing to be dialed in.

The car was tuned in Nebraska, now I moved to Texas. Gas in NE was 91 at best, here it is 93 everywhere. Historically my car has been iffy in the winter time before due to the winter blend, this might just be the very same issue.

IAM is at 1, no knock, car runs like a raped ape, I may just leave it be for now and wait for spring and see what happens.

 

Yesterday AF Learning range A was 12, now it's 7

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The rear o2 on 05+ (or 32 bit ecu) vehicles is used for fueling. This is why we can't just use the spark plug defouler on the rear o2 sensor for a cat inefficiency code.

 

You could try using only open loop fueling and see if it improves. Method found here.

 

Alternatively you can zero out the CL target comp tables at and near idle and your AFR should be extremely close to 14.7. Method found here.

 

Here is what my CL target comp table is set at and my idle is very close to stoich instead of rich.

42378698_CLTable.thumb.jpg.38b5f937ed16c4f4f832ebd1fe5a7929.jpg

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Awesome! That gives me something to chew on. I really hope that'll take care of it. Otherwise I'm out of ideas for what to do next.

I will try going the Open Loop route only and see what I get. If it improves I'll replace the rear O2 sensor and go from there.

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  • 2 weeks later...

I need some help as I am evidently clueless. Tried reading the Cobb manual explaining the tables, still confused. Googled, coming up empty. Basically the issue is I am trying to translate the instructions to ATR. Under Fuel Tables I found Open Loop (Primary) and found the Primary Open Loop Min. Activation and the max value it takes is 1.00 so I am pretty sure I got the wrong one.

Unsure about method 2 as well since my tables look different than the ones pictured. Closed Loop Fueling Target Compensation A and B the only ones I see are coolant temp based

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Using Accesstuner Race

 

To run open loop all of the time:

 

Under fuel tables tab:

Closed/Open Loop transition tab:

Delay tab

Closed to open delays: Set all to zero.

 

Under fuel tables tab:

Open loop primary tab:

primary open loop fueling min. activation: Change value to 14.69.

 

Under fuel tables tab:

Open loop primary tab:

Primary open loop fueling: Change all 14.7 values to 14.68.

 

Save file under new name to accessport and reflash to ecu. Now your car will be in open loop for all values of your primary open loop table below 14.69 (all of the time).

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Thank you sir! The only thing in that list that I know was already done was zeroing out the closed to open loop transition delay.

 

One note though.

i. primary open loop fueling min. activation: Change value to 14.69
Tried this, it only lets me go up to 1.00 and is currently set to 0.98
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Thank you sir! The only thing in that list that I know was already done was zeroing out the closed to open loop transition delay.

 

One note though. Tried this, it only lets me go up to 1.00 and is currently set to 0.98

 

Got it. For some reason your tables must be in lambda instead of air fuel ratio. Essentially your tables are showing the AFR/14.7 values instead of just AFR.

 

Instead of 14.69 in the min. activation change the value to .999 if possible. If you Primary Open loop table is also showing values in lambda (something like numbers between 0.6 to 1.0) change all of the values that are close to 1.0 to .998 (if possible).

 

If it does not allow three place values, just use .99 for min. activation and .98 for the primary open loop table.

 

Hopefully I am being clear. Let me know if it is not.

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I may have found an easier way for you! Your accesstuner race isn't in standard units.

 

Go to edit. Then configure options. Click the display tab. Finally, check the Show Standard Units checkbox and then ok. All of your tables should be in standard afr now.

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Yes, perfectly clear. I'll see if there is a way to change from Lambda, neglected to mention I did see that metric listed in the table. Apologies.

 

LE: ha, such a silly little thing. Thank you! I was wracking my brains over this.

Now cross your fingers this will help me narrow it down to a flaky rear 02 sensor

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Now cross your fingers this will help me narrow it down to a flaky rear 02 sensor

 

Silly me but do you even have that connected? I know some folks do...and rely solely on a software fix, but I recall mine having the resistor mod and zip-tied, unconnected to anything. At least that's how it was 3 weeks ago...Or am I confusing harnesses here ? Or maybe I need a new resistor...

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You are talking about the uppipe sensor and in that case yes, I have mine completely removed and have the resistor mod. The rear O2 sensor is connected at the end of the downpipe. Stock there were 3: front (still there), mid (uppipe removed), rear (downpipe).
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