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Author Topic: Intermittent low boost/half limp, no code yet  (Read 59 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.

Welcome to the forum.
2007 Aggressive GXP

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.


« 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.


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