Help Lean Trouble Codes Maybe Vleak

UPDATED 7/17/05 9:15pm Cen.

Hello!

Ok heres the deal.

I have a 98 Z71 5.7, AT. The truck has surging at accleration, and lack of power. The SES came on, thankfully. I hooked up the autotap scanner and found two DTC codes. They are P0174 and P0171, they came in at the same time. They both indicate fuel trim system lean, i.e. there is to much of a lean fuel condition, and the pcm is having a hard time correcting it and/or cannot correct it. I read on the GM tech boards that if both of those codes come in at the same time, without setting any other codes it is a vacuum leak after the MAF. So I did what all our fathers taught us to do in that situation. Get out the carb cleaner and spray it around the vacuum lines, intake, and TB. Well I did not find any leaks, though I could not spray directy at the back of the intake due to the small fire ball that occured the first time i tried. So, the engine as far as I can tell does not have a vacuum leak that my method could find, as long as it is not at the back of the intake , but I do think that the fog of carb cleaner would have been sucked in back there.

Here is an interesting twist. Prior to the codes being set, and the sluggish, surging, loss of power condtion; I installed a Granatelli MAF, that has cold air tuning, because I have the K&N fipk Gen 2. Granatelli suggest the cold air model due to an aftermarket CAI. I believe there was slight surging before the G MAF, but now it is more prononced due to the fact more air is entering the engine?

Maybe i need the non-cold air tuning G MAF?
There were not any trouble codes ever prior to this.
Any body have any ideas, I can change out parts if I know which ones need to be, I do not want the shop to easter egg a fix.
The intake manifold gasket was replaced close to a year ago, maybe little more than a month left on parts and labor warranty.
I tried to get a hold of granatelli by e-mail because of my screwed up work schedule, but they have not got back to me yet.
I plan on installing the old MAF sensor and see if the condtion/symptoms go away. Thanks for your time reading this! if you have any ideas please let me know. Take Care,

UPDATED;

I hooked up the hypertech scanner to return to stock tuning but keep the tire size axle changes. I read two additional codes:
P0131 o2 sensor circuit low voltage bank 1 sensor 1 and P0151 o2 sensor circuit low voltage bank 2 sensor 1. Cleared DTC's.
I also removed the Granatelli MAF and reinstalled stock MAF.
I will take it for a ride to see if the symptoms have changed, and or if it sets DTC's in the next few days. I will update again.
The o2's low voltage is also indicative of a low fuel lean condition/vacuum leak. I changed my fuel filter a year ago, and regulary run injector cleaner.
thanks again for your time reading this.

Miked73USA

UPDATE 2: 7/17/05 10:10 pm cen

I took the truck for a test drive after warming up to temp. I immediately noticed a signifigant change in throttle response and performance. There was no lag, sluggishness or surging from 1000rpm to redline.
I believe that the G MAF was the culprit and here is why:
The version I purchased was the cold air tuned Granatelli Maf model # 350113-c. Granatelli suggests to use this model if you have an aftermarket CAI. Mine is the k&N fipk 2. Granatellis explains that a cold air tuned model should be used because:
Cold air inductions significantly increase airflow and can cause tremendous turbulence in the air intake stream. When using the GMS mass airflow sensor with any type of cold air induction, high flow induction, or high flow air filter, your GMS mass airflow sensor must be calibrated with cold air tuning or a check engine light can occur. Cold air tuning is designated by a "C" as the last digit in the part number. Cold air tuning is also available for existing GMS mass airflow sensor owners - please call 805-486-6644 for details.

My conclusion is this. The K&N air intake is smooth and not as turbulent as Granatelli states could be. So what in fact is happening, the cold air tuning of the GMAF believes it is compensating for turbulent airflow, where infact it is sending to the pcm a much lower amount air coming in than really is. So no matter where the throttle was at, Much more air was being brought in than the GMAF was measuring and or compensating for turbulent air flow. The real test will be if any more DTC's come back. I will wait to call Granatelli to exchange for there normal model. Also, I have read where people on this forum removed the maf screen from the stock MAF and have not set any DTC's even with having a after market cold air intake kit. Thanks for your time. If you come up with any other ideas, or If I am tottaly out to lunch on this one, let me know. Have a great week!

Mike73USA

Just an idea but I wouldnt use carb cleaner to find a vacum leak. I would use Propane. Carb cleaner doesnt evaporate quickly enough and can ignite if your spark plug wires jump arc

Fuel filter should be changed once a year at least--plugged filter can set lean codes--tho probably not in your case.