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P0171 Code LTFT Maxed @ Idle

dbextreme

dbextreme

New member
Ok I have a 99 GPGT with the mods in my sig along with an Intense custom tuned PCM. I have an Aeroforce that I am scanning with. I have researched and researched, tweeked and tweeked and am about to come up with it's in my tune but wanted to ask here first.

I am setting off my SES light with P0171 code often when my car is cold. Sometimes the P0300 triggers with it, but it’s rare. When I get the code, I’ll clear it/them once I get to where I am going and it will not come up again once the car is warm. This is not daily, but it does happen a couple times a week.

Little background. Once I got the car running I had a 5v reference code. Tracking this down, I shoved the volt meter lead into the TPS plug to far, spreading it out far enough to cause a short. I have since fixed this problem. I have unplugged my battery for a few hours to hopefully reset the PCM since I did drive it like this for several hundred miles.

Now my LTFT’s are maxed out at 16.4 at idle. Once I start driving they look normal which from what I understand to be 0 +/-5. At WOT my LTFT’s are usually locked on 0 +/- 2. Once my car is at op temp my LTFT’s sit at 14.6 at idle. As soon as I take my foot off the gas LTFT’s are back to 14.6 – 16.4. What I have done so far:

• Checked vacuum. No leaks that I can find. My idle is constant with no RPM fluctuation other then “cam”. My vacuum sits at ~15 in-Hg while at idle in park with no movement. In gear it moves to maybe 13 in-Hg which for the XP cam I think this is normal. But there is no movement like a vacuum leak and does not change with engine temp
• Boost is at 9psi WOT
• I have a new AC Delco front O2 sensor from RockAuto.
• I have a homemade extension (Speed Daddy headers) for my O2 from an old harness I had here. If I crossed wires I’d think I would have more of an issue.
• I have pulled my plugs and they all look great
• No rear O2, No cat
• Unhooked my battery for a couple hours. After hooking my battery backup, my LTFT’s where +/- 5 at idle for a day. Next day I was back up to 16.4...

When I changed my supercharger snout, I did get quite a bit of oil on the gasket. Has this ruined my new Felpro gasket? Other then this issue, car runs great. Starts right up and has great power.

Any thoughts or suggestions, willing to try anything? I’m strongly leaning toward tune...
 
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CRAP I just noticed I put this in the wrong section!!! Should have put it in the Supercharged section and not the NA section... Admin move???? :D
 
Have done. Hopefully it looks better and more easily read!!! LOL Thanks for the move and help with the settings.
 
I had this same problem when I ran my new setup on my car. LTFT's were at 16.4 at idle or when I let off the throttle, with what I thought to be "no vacuum leaks." I searched forever and ever and couldn't find one, and I leaned towards it being my tune as well. After spraying enough brake cleaner/carb cleaner, I found the TINIEST leak in the throttle body. Small enough that it didn't even affect my AFR's at WOT, or my vacuum/boost number at idle or WOT. I know you said you checked already, but I'd double/triple check for vacuum leaks. It's rare that our cars show 16.4 LTFT's without a vac leak present.
 


I may have to do the seafoam smoke trick to see what I come up with. I might just take the supercharger off and bet a new gasket, reseal everything and go from there. That's my fear is a slight vacuum leak to. I hate tracking them down!!!

I appreciate it!
 
I would also check around and see if any of your local shops around you can do a smoke test on the car. My high school shop had one of those and it was pretty handy when we'd have to "diagnose" a vacuum leak. If not, well then sea foam and new gasket it is! Good luck on it!
 
Have you deleted the EGR?
If not check the flexpipe going from it to the LIM. I brazed mine up today and problem solved. It was cracked on the EGR side at the flat compression fitting and cracked on the inside of the bend at the LIM.
 


I have the same problem with mine. I just changed the supercharger gasket today and put copper sealant on the gasket. Waiting till tomorrow for it to cure, hopefully thats my problem if not im lost:(
 
Bout 2.5-3hrs away in Summertown.
1hr south of Nashville.

Have you checked your vacuum lines at the Map and SC? Very small cracks can cause hellacious problems.
I replaced all of mine just because I found one small crack.
I wouldn't think SC oil would cause a gasket to deteriorate. Have you done a LIM gasket swap lately?
 
01grandprix are you from decatur AL?

Have you CLOSELY checked the EGR tube? I couldn't visually see the cracks in mine. I put it under water and did an air pressure test and WOW did I get a lot of bubbles! Lmao
 
Nope decatur il. I have when i did my top swap. I took the egr tube off completely and looked at it in the sun to see if light shined through but i never tried putting it in water. I tried a smoke test that i seen with a cigar which sent it out under the snout but ive changed it once 2 months ago, im hoping this added sealant helps. Im just trying to get a few more suggestions if this doesn't work.
 
If the sealant doesn't work,(hopefully it will) take the intake egr pipe off and lightly pressurize it under water.
A Very small crack can cause a bad headache.
 


My motor is a fresh build, less then 1500 miles. I put the new LIM gaskets on when I did the job along with all new vacuum hoses and fittings. :(

I did find a small leak in my cross over pipe due to the crap clamps (I have not put the 2.25" band clamps on yet but will)

I will more then likely pull the supercharger off and Northstar TB and reseal all of that...

Also, the nipple on the TB in the pic goes to my evap. I can pull that line off with the motor running and NO CHANGE!!!! Vacuum doesn't drop, car doesn't sputter, nothing. I remember with my stock throttle body, if that came off the car ran like crap... Wonder if this has something to do with it??? And I wonder why it doesn't change anything with it unplugged?? I'm puzzled...

 
The nipple is probably it (don't pay attention to the electrical tape, the piece is actually fine) but there's NO vacuum on either end... :th_scratchhead:
 
And this maybe a stupid question, but is silicone needed for the supercharger gasket??? I did not use any... LOL
 
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