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Author Topic: Intermittent low boost/half limp, no code yet  (Read 797 times)

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Offline desmo200

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Intermittent low boost/half limp, no code yet
« on: March 17, 2017, 07:05:19 PM »
For the last year, my 07 sky redline with GMPP and 102K miles has been dropping boost. Typically on warmer days after sitting in traffic with A/C running. I have done an intake pressure test and my intercooler has not mushroomed. With my OBD2 unit and Torque app on my phone I have been monitoring fuel trims, the low boost mode seems to come after the fuel trim at idle starts trending negative, sometimes all the way to -30.5%. I expect to get a P2188 code but have not yet.

I think possibly o2 sensor issue but most likely a leaky injector. Any additional insight would be appreciated, I am baffled why it would limp mode without a code.

Offline Sol Asylum

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Re: Intermittent low boost/half limp, no code yet
« Reply #1 on: March 18, 2017, 11:30:40 AM »
Someone with GMPP tune probably knows better than me about this but....

A common issue people had with this mod was problems with the crimp splices used to install the new sensors.  Most people cut the crimps out and soldered the wires.

There are threads here about this that you can search for or maybe someone else that knows the thread might post a link.

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Offline Sly Bob

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Re: Intermittent low boost/half limp, no code yet
« Reply #2 on: March 18, 2017, 11:36:56 AM »
SA makes a good point. Those crimp on connectors that GM supplied with the kit were not the best. Do your self a favor and solder the wires. Worked for this guy and more than a few others.

http://www.kappaperformance.com/forum/index.php?topic=7642.0

« Last Edit: March 18, 2017, 11:43:54 AM by Sly Bob »
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Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #3 on: March 18, 2017, 01:38:14 PM »
I have already soldered the MAP connections. Sorry I forgot to mention that. I have new O2 sensors on the way, they are the next least expensive thing to replace before injectors. Luckily I am still in my extended warranty from CarMax, if I can just get it to throw a code then maybe they will cover it. If you see the chart below I tracked my fuel trims for a period of time, in the middle during idle you can see it drop all the way to -30%. But not always.


Offline elff

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Re: Intermittent low boost/half limp, no code yet
« Reply #4 on: March 18, 2017, 03:11:32 PM »
There is a difference between losing boost and going into Limp mode.  When you are in limp mode, you will 100% throw an engine code and you will not be able to boost more than a couple psi. 

If your fuel trims are bouncing, and you are having issues building/holding boost, but are not throwing a code, I would think you have an air leak somewhere. 

I recently went through the exact same situation.  Turns out I had 2 issues. 
1. Someone replaced the 3 BAR sensor on my Driver side IC Pipe and did not install the Blue O-Ring which is the proper size for the hole in the IC Pipe.  I fortunately had spares
2. My Passenger IC Pipe was slightly crushed from a T-Bolt Clamp being over tightened [My Fault while troubleshooting]

#2 was harder to find because that is where I was connecting my Boost Leak tester and I just happened to notice it was no longer round after I took the tester off.

I was still able to boost over 25PSI, but I could not hold it.  Now my Boost and Airflow are a flat line until I shift.

Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #5 on: April 15, 2017, 12:20:17 AM »
elff, thanks for the info. I did another sanity leak check, but still no leaks.

I have to argue that there is a half-limp mode. I will be all good one minute, able to make full boost. Then usually after idling in traffic or sometimes whenever the computer feels like it, it will only give me about 14psi. Then next time I start the car it may come back, without any mechanical tinkering or fixing leaks. I'm far from an expert but I cannot fathom a boost leak that would be intermittent.

I replaced both O2 sensors and all was fine for a couple weeks, it had been fairly cold weather. But yesterday, a warmer day, I had boost until I was half way home from work, then half-boost. no codes yet.

Offline 2kwk4u

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Re: Intermittent low boost/half limp, no code yet
« Reply #6 on: April 15, 2017, 06:55:30 AM »
Just random thoughts:

Have you monitored/logged your intake air temperature readings (there are two)?  How about coolant temperature?  Could it be a flaky sensor somewhere that's just not flaky enough to throw a reading out of range?

Alternatively, how about the wastegate / bypass diaphragm on the turbo?  Might the heat be affecting something there?

Offline Gentleman Jack

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Intermittent low boost/half limp, no code yet
« Reply #7 on: April 15, 2017, 09:53:46 AM »
When I had weird issues with limp mode it was all related to the tune.
After logging several (hundred?) logs and working with the tuner, we finally got it right.
And boy did we get it right.
Once the tune was correct, it was a different car.
Then I sold it.

Why did I do that?
May the Schwartz be wit you

Offline TomatoSoup

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Re: Intermittent low boost/half limp, no code yet
« Reply #8 on: April 15, 2017, 12:00:06 PM »
"That is my theory, it is mine, and belongs to me and I own it, and what it is too." (Monty Python)

Offline Gentleman Jack

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Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #10 on: April 15, 2017, 01:11:39 PM »
Just random thoughts:

Have you monitored/logged your intake air temperature readings (there are two)?  How about coolant temperature?  Could it be a flaky sensor somewhere that's just not flaky enough to throw a reading out of range?

Alternatively, how about the waste-gate / bypass diaphragm on the turbo?  Might the heat be affecting something there?

I have not looked at intake temps, I will take a look. I have kept an eye on coolant, because I had to replace my radiator fan recently, and cooling stays between 199F - 207F.

I have not done any inspection on the waste-gate or bypass, I frankly have no Idea what to look for. I know what/where they are but do not know how to test their function. I will do some google-ing, any tips would be appreciated.

I am running the GMPP tune, as far as I know there is no changing/tweaking it.

I drove it to work this morning and the first few miles were low boost, to correct my previous post its more like 8psi not 14, then boost came back. It is a chilly day, not running A/C.
« Last Edit: April 15, 2017, 01:22:51 PM by desmo200 »

Offline Gentleman Jack

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Re: Intermittent low boost/half limp, no code yet
« Reply #11 on: April 15, 2017, 05:30:46 PM »
GMPP= bad connectors???
May the Schwartz be wit you

Offline elff

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Re: Intermittent low boost/half limp, no code yet
« Reply #12 on: April 15, 2017, 10:27:13 PM »
I don't think bad connections would cause this intermittent boost issue.
That ended up being total limp mode until a system restart. 

Do you happen to have anyone nearby with HP Tuners?
You could log a lot more to try and see what is going on.

I am still leaning towards you having a boost leak somewhere

Offline Sol Asylum

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Re: Intermittent low boost/half limp, no code yet
« Reply #13 on: April 15, 2017, 10:59:12 PM »
What O-rings do you have on the three bar sensors?  Are they green or blue?
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Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #14 on: April 20, 2017, 11:35:25 PM »
I am still leaning towards you having a boost leak somewhere

I deleted the charge air bypass solenoid. Afterward while driving the first couple times I put my foot down I got low boost, then by the 3rd time it was making full boost. I haven't been able to put many miles on it since. If I keep having issues I will have to look at the waste-gate solenoid and vacuum lines.


What O-rings do you have on the three bar sensors?  Are they green or blue?

Blue

Offline Sol Asylum

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Re: Intermittent low boost/half limp, no code yet
« Reply #15 on: April 21, 2017, 12:30:11 AM »
Others can correct me if I'm wrong but the blue ones are what should be installed so you should be good there.
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Offline THe_Ghost

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Re: Intermittent low boost/half limp, no code yet
« Reply #16 on: April 27, 2017, 09:47:19 AM »
@ Desmo200 - You can pull "pending codes" if you have the Torque app.  And you can clear it before it sets.  Just scan for codes and it will give you the pending codes.  Mine does what you're describing when the p2188 code pends.  In other words, it's getting ready to turn the CEL light on, it just hasn't hit the parameters for that yet.  I'm a regular on the Solsticeforum, and have been chasing my p2188 code and occasional backfiring on decel for over a year.  You have the same exact symptoms I have....STFT drops to -30.5...AFR is < 14.3....  I think I've finally figured out that I need a HPFP.  I'll know this weekend.  Have you smelled your oil?  Does it smell like gas?....It might with the p2188 code which usually means a HPFP or leaky injector.  More likely thought its your HPFP.  One quick way to look for a leaky injector is to watch your fuel rail pressure when you turn the car off after it's warm....it should rise as the fuel boils.  But that doesn't necessarily mean you have a leaky injector.  Since I don't visit here much, i'm not sure how much you've been told or how much you know....

http://www.youtube.com/watch?v=4M9BITr1zhg

Quote
I deleted the charge air bypass solenoid.

EDIT:  If you have an alternative method for charge by-pass other then the factory with GMPP, that's an issue.  Was the tune a GMPP tune that was customized for that BOV?  If not, that has to be fixed first.  And I'll save you a bit of time, the LNF doesn't really like the vent-to-atmosphere BOVs.  People have had success with the BOV, but a lot go back to the OE version.  You're too rich at idle because the car is looking for that metered air and it's not getting it, you're venting it if your tune was not setup for the BOV.
« Last Edit: April 27, 2017, 10:00:42 AM by THe_Ghost »

Offline elff

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Re: Intermittent low boost/half limp, no code yet
« Reply #17 on: April 28, 2017, 11:20:39 PM »
I deleted the charge air bypass solenoid.

Put everything back to stock and see if that resolves the issue.

Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #18 on: May 04, 2017, 12:23:14 PM »
Regarding deleting the charge air bypass solenoid:

1. I did this because I was having boost issues, I am still waiting to see if my low boost issue comes back since I have done this
2. The stock charge air bypass (BOV) is still in place and connected directly to the vacuum line, it is the solenoid that was deleted.
https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/bypass-valve-fix-possible-boost-mod-191361/

Offline THe_Ghost

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Re: Intermittent low boost/half limp, no code yet
« Reply #19 on: May 05, 2017, 07:17:46 AM »
My understanding is DO NOT MESS with anything related to boost unless you get retuned.  These cars are finicky when it comes to that.  So you're saying you're not venting to atmosphere with your BOV?  That it's returning the air to the car?  If you're having boost issues, the first thing to do, especially if you just bought the car, put the tune back to the OE tune.  Figure out your issues with that, then start modding the car.  Otherwise there are too many variables.  It could be your tune or it could be mechanical.  And from what I've read about your rerouting of the bypass air, it doesn't really work on the Kappa platform....if it did, it would be a major discussion continuously.  And this is the first I've heard about this in 4 years...
« Last Edit: May 05, 2017, 11:19:27 AM by THe_Ghost »

Offline elff

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Re: Intermittent low boost/half limp, no code yet
« Reply #20 on: May 05, 2017, 10:21:27 AM »
have you tested the waste gate actuator?
it might not be holding the waste gate closed and be bleeding boost.  You do have a lot of miles on the car.

Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #21 on: May 23, 2017, 02:18:18 PM »
My understanding is DO NOT MESS with anything related to boost unless you get retuned.  These cars are finicky when it comes to that.  So you're saying you're not venting to atmosphere with your BOV?  That it's returning the air to the car?  If you're having boost issues, the first thing to do, especially if you just bought the car, put the tune back to the OE tune.  Figure out your issues with that, then start modding the car.  Otherwise there are too many variables.  It could be your tune or it could be mechanical.  And from what I've read about your rerouting of the bypass air, it doesn't really work on the Kappa platform....if it did, it would be a major discussion continuously.  And this is the first I've heard about this in 4 years...

I put 25-30K miles on it with the arguably stock GMPP upgrade before I started having issues, deleting the solenoid is my only other mod and was a dart throw to see if I was losing vacuum through it while driving since I have no detectable leaks from a pressure test.

And I'll repeat myself:
The stock charge air bypass (BOV) is still in place and connected directly to the vacuum line, it is the solenoid that was deleted.
https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/bypass-valve-fix-possible-boost-mod-191361/

elff:
I have not tested the wastegate actuator yet. How do I test it? How would I know if it is working properly? I have about 103K miles on the car.

Everything was working great the last couple weeks, it has been cool outside and I don't need the A/C. However today is a bit warmer and with the A/C on for a little while I couldn't make full boost. No code. I'll have to look at my fuel trims again. Still leaning toward HPFP or injectors. I hoping it shows a code and try to take advantage of my CarMax warranty.

Offline THe_Ghost

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Re: Intermittent low boost/half limp, no code yet
« Reply #22 on: May 23, 2017, 03:50:14 PM »
Does your oil/dipstick smell like raw gas?

Offline desmo200

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Re: Intermittent low boost/half limp, no code yet
« Reply #23 on: May 23, 2017, 06:26:50 PM »
Does your oil/dipstick smell like raw gas?

Nope

Offline Gentleman Jack

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Re: Intermittent low boost/half limp, no code yet
« Reply #24 on: May 23, 2017, 11:29:40 PM »
Can you return everything to stock( replace the solenoid) and then pull fuse 42 for an hour.
(Or, disconnect BOTH battery cables and then touch the two cables together)

This will wipe the entire memory and return the car to the way it was built.

Leave the gmpp tune for now.

Let me know how that goes.
May the Schwartz be wit you

 

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