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1g leaning out at idle and passed 5,000rpms under boost

GettinPaper

Proven Member
289
0
Aug 31, 2009
Battle Ground, Washington
Too start it off my mods are dejon MBC set at 12psi,a 3" straight pipe exhaust(ported the 02housing and turbo hotside for creep it holds steady boost to redline), dejon hard intake pipe and a walbro 255. I have zero boost leaks also. I have a AEM wideband and it reads 16.5 to --- at idle. And 10.0 under boost until 5,000 Rpms then it shoots up to 12.8-13.5.. What would be causing me to lean out at all?? Any help is appreciated.. Thanks
 

Phantom DSM

Proven Member
568
12
Jan 28, 2007
Dallas, Texas
Assuming the pump and fuel pressure regulator are fine, usually the fpr gets overrun by the bigger pump and should be richer.
After a good drive and motor off if you take vacuum hose off the fue pressure regulator, does it smell wet with gas?
Is the pump rewired? if you can take voltage right at the power wire in the harness connecting to the pump assembly, what does it show?
12 psi of boost is not much to max out the 450s, The 1g stock map is aggressive and should have around 10 a/f ratios on high rpm, seems like low voltage to the pump..had the same issue.
 

thomcasey

Proven Member
949
25
Dec 16, 2009
Indianapolis, Indiana
I had the same issue. Thought I was pre-WB exhaust leak free. THEN, my downpipe broke at the flange weld where it bolts to the o2 housing. Put on a new downpipe, ensured no leaks, worked AFR's back to normal
 

GettinPaper

Proven Member
289
0
Aug 31, 2009
Battle Ground, Washington
I don't smell wet gas from the vacuum line on the fpr, the pump is not rewired. I will check the voltage and get back to you

I just started my car and my wideband is satin po1 and po2 and reading 1.22 at idle.. What is this? Bad 02? And after a minute of driving it went back to normal..
 
Last edited:

GettinPaper

Proven Member
289
0
Aug 31, 2009
Battle Ground, Washington
So I went ahead and replaced the fuel pump with a brand new 190 and said screw the old one. I am still leaning out past 5grand, on the way to work this morning I went to do a second gear pull and right when it usually leans out it started sputtering so I backed off... What in the hell can be causing this to lean out and now starting to sputter? Any help is appreciated, thanks.
 

Spoolingaround

Proven Member
131
6
Nov 6, 2013
Tucson, Arizona
Where do you have your boost gauge Teed off at? If you Teed it of at the vaccume line of the fuel pressure reg that can mess with your fuel pressure.

Also, whats your idle fuel pressure?
 

Spoolingaround

Proven Member
131
6
Nov 6, 2013
Tucson, Arizona
Brand new fuel filter and actually my boost gauge is t'd into the fpr line and I don't know my idle fuel pressure it's all stock for the most part

I used to have mine T'd at the FPR until someone told me about how if you have a boost leak there it can drop the fuel pressure when under boost, causing you to run lean, and possibly lean enough to knock and make stuff go boom.
 

navyissuedsm

Proven Member
42
0
Oct 20, 2013
Mountain View, California
I would look into testing your O2 sensor to make sure that you are in fuel control there, and also look into doing a compression test.

wouls also consider doing a system pressure test all the boost leakes in the systemway up to 20psi. that will rule out any boost leaks in the system.
 

Spoolingaround

Proven Member
131
6
Nov 6, 2013
Tucson, Arizona
Well I have to pass emissions and I don't know if it will leaning out at idle.. What do you guys think?

Running lean at idle shouldn't make you fail emissions.

I would look into testing your O2 sensor to make sure that you are in fuel control there, and also look into doing a compression test.

wouls also consider doing a system pressure test all the boost leakes in the systemway up to 20psi. that will rule out any boost leaks in the system.

+1 on the boost leak test, I would be skeptical of the fuel pressure reg and/or a boost leak around it.

I doubt however that an O2 sensor would cause this problem. Im assuming that when you're running lean around 5k rpms you're in open loop (IE no feedback from the O2 sensor is used)

Could also be injectors but I would check the fuel pressure before changing anything.

Also, is your MAF sensor hacked? Cause this kinda sounds like that could be it too.

Also, do you have anything to monitor knock? You may be knocking @ 12lbs and a 13.x on the A/R.

Also, sorry about all the also's ;)
 
Last edited:

curt-s

Proven Member
1,484
263
Dec 21, 2008
Winterville, MB_Canada
If they're the original injectors, they just might be tired and not firing properly anymore, or cannot recover fast enough at higher RPM.

Anything to read sensor/trim values? Even MMCd? So many things..
 
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