Surging/bogging issues, wall of text

[baconbits]

All,

 

I just realized I have a worrying (at least for me being new to Subarus) issue with boost today.

 

Starting with mods:

• Cobb AP with OTS stage 2, 93+SF map
  
• Cobb short ram intake (no box yet) (cleaned MAF when installed less than 1k miles ago)
  
• Invidia catted downpipe
  
• Custom 3" straight through catback
  

 

Car is a 2006 5mt LGT. Spark plugs were OEM dealer replacements put in less than 5k miles ago. Car has 91,2xx on it. I have a Shell gas station 3 blocks from my house so 99/100 times, I'm filling up with 93oct there. Weather here has been high 60s, low 70s for the past couple days, average humidity, no rain.

 

Now to the issues (This has happened all of a sudden, in the last day or two.):

Cruising along on the highway between 60-70mph, there's a hesitation at times, and other times there's a slight shudder that can be felt, almost like the engine stumbles.

 

When accelerating (from a light/stop or gear to gear), it's almost as if the car stumbles as soon as the clutch is fully out. It's not like the car is going to stall, but it's definitely noticeable. If I lay into the gas pedal, the stumble is more severe and much more noticeable for someone who isn't paying attention to it (ie: girlfriend asking "wtf was that?").

 

When hammering second gear, I can manage 9psi MAX before it falls to 8ish. Hammering third gear, it climbs to 8psi or a hair over, and then falls to a hair under 8psi. This is all according to my Accessport. I don't have a boost gauge.

 

When driving around recently, I noticed my AP was telling me my fine knock learning was 0.7. Thinking that was odd, I went to my knock sum which said 5/5. I thought that was also odd, because I did a couple 3rd gear logging pulls a month or two back when air temps were 20 degrees hotter and all four cylinders registered zero knock (this was back when I had a stock intake on there). Thinking that knock stuff was weird, I unplugged and plugged back in my AP while cruising at 35mph (deserted road, etc ) and then immediately went to knock sum as soon as I could, where it said 7/7, again while cruising. Jamming on the gas in second or third gear did not change the numbers at all.

 

 

Things I've checked today:

• TMIC has no leaks at the seams, no cracks
  
• Blue T under TMIC is exactly as I left it a couple weeks ago when I added zip ties as a preventative measure
  
• Turbo/TMIC gasket appears okay
  
• TMIC/BPV gasket seems okay
  
• Throttle body hose seems to seal on both ends (fixed earlier today, thought it was the issue first)
  

 

I wish I had a boost leak tester. I could probably make one this weekend, but won't be able to use it til Monday when I could use the shop air (with a regulator).

 

I've been offered a known-good stock BPV and stock TMIC for testing, and I can throw my stock intake back on if someone thinks it will help. I'm going to clean my MAF again tomorrow (just in case the Cobb filter was oiled too much). I have reset my ECU via the AP but have not driven it since.

 

Toughts? :confused:

[Nolmers06LGT]

If it's due to the intake, it would be overboosting, not underboosting, so that's out. Can you log it with your AP? It sounds like a severe leak post turbo, which I would think you'd be able to hear, or maybe fueling. Worst case, your turbo is letting go, but I would think there would be noises associated with that also. It would be nice if you could pull a learning view. I've had some fine learning knock and some partial throttle hesitation lately- I'm also running rich so I'm thinking I've got a boost leak, however you're losing A LOT more boost than I.

[baconbits]

All of those issues were at partial or full throttle. Regardless...

 

I reset the ECU via my AP and it seems all the issues have gone away other than those first couple miles where the car needs to relearn itself. I can make 16psi in 3rd and 4th gear and it feels fine.

 

There is a loud flutter noise for boost under partial throttle though... like put it in 3rd and run half throttle up to 5000rpm or so... I probably just never noticed it before and it's completely normal.

[Nolmers06LGT]

Well that's good. You may just be noticing it now because of the cool air. In any case, you're still probably due for an LV and a boost leak test.

[baconbits]

Well that's good. You may just be noticing it now because of the cool air. In any case, you're still probably due for an LV and a boost leak test.

 

Yep, definitely.

[thefultonhow]

You should have checked DAM on your AP before you reset it. DAM on AP = IAM on open-source. Most likely, DAM was at 0 due to the problem with your TB hose.

[MasAyinde]

Want a boost leak tester? I have a couple laying around and I can send you one

[Max Capacity]

Make sure the TB hose has not blown off the TB.

 

My wagon was surging before the tranny had it's issue. (broken main shaft).

 

Since the mechanic put the TB hose on well, the car feels so much better. I kind of thought that was the problem causing my surging under high boost.

[baconbits]

Make sure the TB hose has not blown off the TB.

 

My wagon was surging before the tranny had it's issue. (broken main shaft).

 

Since the mechanic put the TB hose on well, the car feels so much better. I kind of thought that was the problem causing my surging under high boost.

 

Well, when I noticed the problems first started, I pulled the TMIC off to check the blue T.

 

I loosened the clamp at the hose/TMIC connection, went to pull the TMIC off, and the hose came off the TB without me loosening that clamp. I thought that was the issue for sure, but then the test drive told me it wasn't.

 

What should I look for with the DAM on the AP? I'm still learning how to use the AP as a diag tool... not sure what's good and bad for readings.

[heiche]

The IAM or DAM should be at 1.000 for normal operation. If that drops, it indicates that the ECU has seen something out of range (like a lot of knocking). When the IAM/DAM reduces below 1 timing starts to get pulled, and if it goes low enough then boost is limited too.

 

So my guess is that it WAS the TB hose that caused the issues and probably dropped your IAM/DAM. You then fixed the issue (tightened the clamp) but the IAM/DAM was still low as it takes a little while to creep back up under good conditions. When you then reset your ECU, it zero'd out all of the (bad) learned values, and let the IAM/DAM get back up to 1.000 very quickly.

 

I'd keep an eye on it, but sounds like you got it.

[Nolmers06LGT]

The IAM or DAM should be at 1.000 for normal operation. If that drops, it indicates that the ECU has seen something out of range (like a lot of knocking). When the IAM/DAM reduces below 1 timing starts to get pulled, and if it goes low enough then boost is limited too.

 

So my guess is that it WAS the TB hose that caused the issues and probably dropped your IAM/DAM. You then fixed the issue (tightened the clamp) but the IAM/DAM was still low as it takes a little while to creep back up under good conditions. When you then reset your ECU, it zero'd out all of the (bad) learned values, and let the IAM/DAM get back up to 1.000 very quickly.

 

I'd keep an eye on it, but sounds like you got it.

 

Makes sense.

[baconbits]

That's what I was thinking... still learning the diagnosis stuff like that.

 

Thanks for the explanation.

[SBT]

Stock turbo correct? Or did I miss that.

 

If stock turbo, I'd check the wastegate arm bushing to make sure that it hasn't come loose and forced the wastegate arm toward the outside of the turbo, approximately 1/4"-3/8". This would then move your WG almost halfway across your WG port, which means that you'd lose boost at/about 10psi.

 

This happened on a cross-country trip and I replaced it with a VF46 that I had with me. Fixed the issue immediately.

[SBT]

If you can move your WG arm in and out against the bushing, that would be a tell-tale sign. Pulling the DP and working the WG arm in and out would be the visual clincher. If you see it moving across the WG port, there's your issue.

[JmP6889928]

I'm guessing front O2 sensor is bad. They don't necessarily set a CEL and it can cause surging and lagging without showing up much. Check your STFT and see if it's bouncing all over the place between -25 and +25. If you see those numbers, change it with one you know is good and I'll bet it clears everything up.