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Discussion Starter · #1 ·
As a lot of you know, I’ve been experiencing very odd behavior out of my car. From not getting full boost in 4th and 5th, to having a HPFP stutter. I haven’t set a CEL yet. So as I was sitting in the parking lot at work, letting the car idle to cool down from my hard freeway drive in, the HPFP was stuttering again….so I decided to data log it. My AFR is all out of whack!!! From all of my previous data logs, my AFR has always been 14.4 – 15.2 (average at idle)…..todays was 11.4 (average at idle) while the car was commanding 14.7. The only thing that I’ve done in the last couple of weeks was clean the MAF. I’m wondering if it didn’t go bad or if I might have a stuck valve. The car seems okay…still quick, no miss that I’m aware of…. Any help from you guys would be great. Here’s my data logs:

Before AFR around 14.7


My idle this morning:
 

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You might get a better response from more knowledgeable ppl at HP Tuners Forum

Yogi
 

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Discussion Starter · #4 ·

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Go and take a look at your MAF, make sure while you cleaned it, there were no damage done or you did not installed it back correctly.
 

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Your fuel rail pressure looks high. I just looked through a few of my logs and my fuel pressure is between 200-380 at idle. Commanded is ~220psi.

Also in you sig...what do you mean your tuned?
 

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Discussion Starter · #8 ·
Your fuel rail pressure looks high. I just looked through a few of my logs and my fuel pressure is between 200-380 at idle. Commanded is ~220psi.

Also in you sig...what do you mean your tuned?
I know that my car is tuned....I just don't who did it. Here's what I know about my tune. It sounds like a WRX until about 2k rpm. (it has that "miss" sound to it). My rev limiter is set at 7k. I see 22psi. I have contacted Trifecta and Worster's and neither have touched my car with a tune. My "part number" (for the tune) in my ECM is not the original GM part number. There are 6 "part numbers" that make up the GM and GMPP tune and mine doesn't match any. How do I know this? A GM engineer friend pulled all of my ECM info, but was unable to look at my tune. I believe that my car was tuned for optimum fuel economy at 75mph+ as I can average about 42mpg at 80mph. I bought my car used from a dealer here in Detroit 3 years ago. From my research that I've done on my car, I found that the PO lived about 80 miles away from his job in Chicago. How do I know where he worked? When I pulled my driver's seat apart to fix and issue, he had done some "engineering" and wrapped a board in a sweatshirt from a glass company with his name on it. There were other items with his name and address in the car. I also have a really bad issue when my car is cold. I cannot get into boost until about 170 degrees or my car literally slows down instead of speeding up even though I see boost pressure. What I believe is that the guy was learning how to tune and never finished the tune. I also think the car got repo'd from him as it went to auction about 19 months after he bought it without going to a dealer first.

With that said, I can tell you that my AFR has always been a little higher then what I thought was safe. At times its gone as high as 21. And many times at idle I'll see 14.9, 15.0. My fuel rail pressure has always been 480-600 at idle. So Brap, this is my background on my car.... Maybe you can help out a bit. If you need more of a data log to look at, let me know!

I purchased a dyno tune from ZZPerformance during their black Friday sale, but I haven't had the time to get over to Grand Rapids yet to get it done.
 

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That afr is normal. It will fluctuate near 14.7 within a point and trims will adjust it. I would try to make time to get down to ZZP asap and have them dial your car in. May fix all your issues and if you do have any mechanical issues they may know just from the logs. As for your fuel economy, if the prior owner adjusted the fuel mass your economy could be way off. The fuel mass would be raised for e mixtures and if you are running gas you would get a reading skewed high. I would top the tank off, drive it empty, fill up again and figure out your fuel economy that way. Is your speedo accurate? Maybe he had different wheels and calibrated for a new tire size. Check with a gps. Also log your long term and short term fuel trims on your next drive.
 

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Not to side track this discussion or throw out a curveball. My 2007 is stock and I've never seen the fuel rail pressure below 500psi. with a brand new HPFP. I'm very curious about 200 - 380psi at idle having the latest updated software.
 

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Interesting. Not a side track at all if the information is wrong. I even have GMS1 logs showing this since I got the car and never adjusted the fuel pressure settings in that area. Been tuning it since 2013 and the idle pressure is always the same. Its a cyclical bump with the hpfp ticking. It doesn't hold steady at idle, just under a load. Maybe I am the anomaly here(though it is commanding 220 which is still way under). I am curious now...I am going to look at some random lnf logs on the forum to see what the fuel pressure is like at idle.
 

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Discussion Starter · #12 ·
What I found interesting this morning was that my AFR actually falls after my freeway drive when I idle my car. I've always idled my turbo cars after freeway driving for a minute or two. While I was sitting this morning I watched my AFR go from 14.8 to 11.9 in about 3 minutes. The fuel pressure stayed between 440 and 660....of course spiking to 660 during the "machine gun" tic cycle. Someone had mentioned that maybe I was tuned for e85 but I would think that I couldn't run on normal 93 octane without issues. If indeed the fuel rail pressure should be less then 300 at idle, I need to get this checked out ASAP! Please let me know what you find!

EDIT: My tire size is correct, my speedo is correct and my MPG is correct....I've checked everything prior....
 

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ALL of my HP Tuner logs show desired pressure of 240-250 and actual pressure of 235-245 at idle.
 

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Ghost, I have little knowledge in this area, and so this is guesswork, but I would say your best bet is to get a known good tune and overwrite whatever was on your car from before.

It's increasingly sounding like that tune is whacked. (That's a technical term :))
 

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Discussion Starter · #15 ·
What would be the highest you’ve seen GXP-Coupe? I was just looking at a log and the highest pressure I saw was over 2100 at 68% throttle and over 4k rpms.

Yep....tune coming Soup!
 

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Discussion Starter · #17 ·
I fixed my machine gun HPFP issue!!! I cleaned my MAF again. At this point it seems to have fixed the weird AFR and HPFP issue!
 
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