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Discussion Starter · #1 ·
Hello Board,

I have been receiving the above mentioned codes randomly for the past few months although they seem to be getting a little more common place.

The codes are either together or is only the P0171 Code

They only appear at start up or when idling

Here are my engine mods:

VCM CAI
Kooks Mid-length headers
Magnaflow cross pipe muffler
GXP Mufflers
Livernois Tune

The car appears to me to run fantastic and sounds amazing, however, I am noticing lower MPG on long trips when the cruise control is set. For example, on a 120 mile trip to Fort Lauderdale last night, I was at 66 mph average with just under 20 MPG. There was no heavy pedal!!

Using my Dashboss, I have been reading 9.37% on my Long Term Fuel Trims during my cruising speeds and way up in the teens and even 24% today at idle.

I have been in contact with Livernois on several occassions and they persist in saying that there is a vacuum leak somewhere.

Today I replaced the two rubber boots around the Throttle Body and VCM and it made no change to LTFT (24%)

I replaced the PCV valve tubing connected to the back of the VCM to the left side PCV valve coming out of the head with fuel line connected to the metal tube and a brass fiting connected to he back of the VCM to ensure a tight fit and it made no change in LTFT (24%)

I inspected all the visible PCV hoses, took them off and plugged them with my thumb and no change in LTFT

I cautiously sprayed MAF Cleaner around the various hoses and fittings to see if engine idle would change; it did not.

I disconnected the harness to the MAF and LTFT did drop down to about 10% but I got a MAF CEL code.

The car does not sputter or surge and appears to me to have plenty of power.

I do intend to take it to a Dyno shop shortlyto do some runs and monitor the wideband O2 sensor as I do not have this capability yet with my Dashboss; however, Livernois suggested I not do that until the leak has been found.

What else can it be? Am I missing something?

I would appreciate any and all feedback as I am now beginning to get frustrated!!:whine:

Perhaps I can put my OEM Airbox back on and see if that changes the LTFT's? Other ideas?

Thanks in advance.
 

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Have you checked the fitting on the back of the intake that goes to the brake booster??? I have seen that hose swell and cause those lean codes....
 

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They show about 14 things that might cause either, or both of those codes. If the list is printed to show the most, to least likely cause, I can see why Livernois is telling you what they think you should be looking for. Vacuum leaks is the first item listed (that would not cause some other type of fault code to set). Other things listed are exhaust leaks from the H02s back to the engine. Evap leaks from the fuel tank to the engine, to possible faulty HO2s sensors, plus the things you've checked. Most of those would have caused other fault codes to set, if they were faulty.
 

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Check your 02 sensors
 

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It is your VCM intake. There is unmetered air. Coming into the motor from the pcv system. The design of the vcm puts the pcv system hose before the maf directly behind the filter. Since the pcv system sucks in air that the maf never reads the air so at idle your fuel trims shoot way up as the car tries to compensate for all the unknown air. I am sure when you hold the car at part throttle your ltfts drop back to normal as there is no longer vacuum. You need a tune that will comensate for this.
 

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Discussion Starter · #6 ·
I appreciate the responses.

Livernois has tuned for the VCM on many occasions and I am certain that they have the right parameters in place. However, I will mention the PCV location for them to make sure.

I know Zep has a VCM and does not get any codes so perhaps I can have them send me his tune to see if there is a difference.

Livernois mentioned that it could be a bad MAF sensor and so I will test a different one on the car as soon as possible to see if that makes a difference.

Eventually I will eliminate the issue.
Appreciate the help so far

Aussie
 

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I appreciate the responses.

Livernois has tuned for the VCM on many occasions and I am certain that they have the right parameters in place. However, I will mention the PCV location for them to make sure.

I know Zep has a VCM and does not get any codes so perhaps I can have them send me his tune to see if there is a difference.

Livernois mentioned that it could be a bad MAF sensor and so I will test a different one on the car as soon as possible to see if that makes a difference.

Eventually I will eliminate the issue.
Appreciate the help so far

Aussie
I am 99% sure that this is the cause bro. If you data log the car at idle, and close off the pcv opening that is where the passenger side fuel runner is I assure you that your LTFT's will drop to normal again. It is definitely the PCV system pulling in unmetered air do to the location of the VCM pvc valve being before the MAF. I was having the exact same issue as soon as I swapped from a rotofab to the VCM. I had everything checked. Headers, intake manifold, all the vacuum hoses etc etc and had a ton of "car people", a dealer and a shop owner check over the car as well. It took a guy at the track pointing out to me when the light when on and I said "oh yeah". If you look at every other intake out there all of them have the PCV hose connect behind the MAF and not before for this very reason.

If you data log it at idle and the various RPM's and send it to your tuner I'm sure they will send you a tune to compensate for it. If you have the car dyno tuned you wouldn't see the code any more either.
 

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I appreciate the responses.

Livernois has tuned for the VCM on many occasions and I am certain that they have the right parameters in place. However, I will mention the PCV location for them to make sure.

I know Zep has a VCM and does not get any codes so perhaps I can have them send me his tune to see if there is a difference.

Livernois mentioned that it could be a bad MAF sensor and so I will test a different one on the car as soon as possible to see if that makes a difference.

Eventually I will eliminate the issue.
Appreciate the help so far

Aussie
I am 99% sure that this is the cause bro. If you data log the car at idle, and close off the pcv opening that is where the passenger side fuel runner is I assure you that your LTFT's will drop to normal again. It is definitely the PCV system pulling in unmetered air do to the location of the VCM pvc valve being before the MAF. I was having the exact same issue as soon as I swapped from a rotofab to the VCM. I had everything checked. Headers, intake manifold, all the vacuum hoses etc etc and had a ton of "car people", a dealer and a shop owner check over the car as well. It took a guy at the track pointing out to me when the light when on and I said "oh yeah". If you look at every other intake out there all of them have the PCV hose connect behind the MAF and not before for this very reason.

If you data log it at idle and the various RPM's and send it to your tuner I'm sure they will send you a tune to compensate for it. If you have the car dyno tuned you wouldn't see the code any more either.
 

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I appreciate the responses.

Livernois has tuned for the VCM on many occasions and I am certain that they have the right parameters in place. However, I will mention the PCV location for them to make sure.

I know Zep has a VCM and does not get any codes so perhaps I can have them send me his tune to see if there is a difference.

Livernois mentioned that it could be a bad MAF sensor and so I will test a different one on the car as soon as possible to see if that makes a difference.

Eventually I will eliminate the issue.
Appreciate the help so far

Aussie
I am 99% sure that this is the cause bro. If you data log the car at idle, and close off the pcv opening that is where the passenger side fuel runner is I assure you that your LTFT's will drop to normal again. It is definitely the PCV system pulling in unmetered air do to the location of the VCM pvc valve being before the MAF.

I was having the exact same issue as soon as I swapped from a rotofab to the VCM. I had everything checked. Headers, intake manifold, all the vacuum hoses etc etc and had a ton of "car people", a dealer and a shop owner check over the car as well. It took a guy at the track pointing out to me when the light when on and I said "oh yeah". If you look at every other intake out there all of them have the PCV hose connect behind the MAF and not before for this very reason.


Then again that 1% could be a bad maf. If it is unplugged does the car throw a code for not reading anything? Mafs are like 60 bucks I believe.

Keep us informed.
 

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Discussion Starter · #10 ·
Well, I'm still working on this but today I cleaned the MAF and no change.
I took the PCV valve tube off from the passenger side head and plugged it with my thumb. No change to LTFT's and it sucked my thumb like a new born. I'm guessing normal.

I am away at the outlaws this weekend and so will have to wait til Monday to keep working on it.

I have had the intake for over a year now with no issues really and so I question it is the intake but I will keep searching and looking at your replies.

I'll put the oem box on Monday with the stock tune and see what happens.

I have a sneaky suspicion it is a leak in the elbow of the pcv valve in front of the drivers side. I have done a lot of searching on Google and this seems possible.

Couple of questions:
Can our MAF sensor be removed from the MAF housing or do you have to remove the entire thing?

Do our cars have a green valve stem in the engine bay to gain access to the vacuum system so that you can blow smoke through it and determine where the leak is?

AD
 

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Yea, is that tube that breather comes across the front / top of the engine, to inside the left-car-side of the back of the vcm intake firmly seated into the hole, with no leaks?

I had to arrange the hose clamp on the rubberized boot of the VCM to be on that same side, so I could somewhat "hook" the breather hose deep within the VCM. No leaks on mine.

Might also be a good idea to trace that line to look for cracks, stretch-marks, and cuts.

Not sure if I'm just repeating what others already said here, I'm coming into this conversation a bit late, and for that I apologize.

As I said via email to you earlier, those fuel trims are way off and need to be fixed asap.

--zepcom
 

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Discussion Starter · #12 ·
Yea, is that tube that breather comes across the front / top of the engine, to inside the left-car-side of the back of the vcm intake firmly seated into the hole, with no leaks?

I had to arrange the hose clamp on the rubberized boot of the VCM to be on that same side, so I could somewhat "hook" the breather hose deep within the VCM. No leaks on mine.

Might also be a good idea to trace that line to look for cracks, stretch-marks, and cuts.

Not sure if I'm just repeating what others already said here, I'm coming into this conversation a bit late, and for that I apologize.

As I said via email to you earlier, those fuel trims are way off and need to be fixed asap.

--zepcom
I replaced that hose the other day with fuel line and a brass fitting mounting into the VCM. It's a great fit as far as I'm concerned.
 

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I narrowed mine down to the PCV system because I saw the changes of my LTFTs at idle when I plugged the pcv valve. Thats how I knew mine was the unmetered air before the Maf. It is the front O2's that cause that code so either they are somehow bad, or your MAF must have taken a dump is what I'm thinking.

When I unplugged my maf while trying to track down the issue my fuel trims returned to normal before throwing a code for the maf not being connected, so you could try testing that. Just start the car with the Maf unplugged and see where your LTFTs go. Mine dropped from 24 to 0 within the matter of a minute before throwing a Maf code.
 

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Discussion Starter · #14 ·
Yes, I have unplugged the MAF and it did exactly what you said. LTFT's dropped to zero before the code registered. Plugged it back in and up to high teens and up to 24 again.

I do notice that when I turn the car off, I hear what almost sounds like a sneeze coming out of the VCM.
Someone told me that it is the butterfly valve in the throttle body shutting but in the 3 years I have had this car I have never heard it before but I've never been listening for it either. I'll try to upload a video of it.
 

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yup. My rotofab and VCM do that. My friends 300SRT8 does that as well.
 

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Discussion Starter · #17 ·
I took a video today of me blocking the PCV Valve on the left side rocker cover (as you are facing the engine) and noticed the LTFT's dropping to somewhat normal ranges.
After releasing the blockage, air was sucked into the system and LTFT's increased back up to the high teen's and up to 23%.

Any ideas on this?
Normal?
Is the unmetered air causing the high LTFT's issue?

 

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As has already been stated... this issue is caused by the PCV being pre-MAF with your intake. A tune to compensate for it will indeed fix the issue.

Additionally, what's the scanner that you're using with the iPad? Are you happy with it? I've been looking into getting one for a while now but haven't settled on anything yet.
 

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Discussion Starter · #19 ·
The scanner is a Dashboss, a very handy tool to have.
There are dozens of parameters that can be viewed on almost any car with a OBD II connector.
 

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Awesome, thanks for the information. I wondered if that's what it was as you mentioned it in your first post but I hadn't heard of it before.

Good luck with tracking down your issue.
 
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