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3" Turboback causing lean A/F?

WaRrIoRs16

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Mar 23, 2008
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373
Location
Ferndale, WA
I haven't drove my galant too much in the past year, but I was driving it just the other day and I noticed that my exhaust is popping every time I'm decelerating. Also I hooked the logger up and noticed that all of my fuel trims are in the 130%'s, none are maxed out but they are all still way up. I also did a 3rd gear pull to from 3k to 7k and got knock that increased as rpms increased up to 23 counts and it dropped to 0 immediately after I let off. I don't ever see knock besides at WOT. I don't ever recall seeing any knock period prior to having the 3" exhaust installed.

So my question is if just installing a 3" exhaust system on a stock VR4 can cause a lean A/F ratio and if that could also be a reason for knock. I know that there are many other things that can cause knock, but I was just seeing if fixing the lean condition could remedy it. If the exhaust system might be the culprit, are their any other bolt-on's that I could get to fix the ratio? I have a walbro fuel pump and a regulator on the way now, but I don't really want to get into any heavy tuning quite yet. Thanks.
 

SouthCaliVR4

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Jul 31, 2010
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North county San Diego
I have a 3" turbo back & never saw my trims get out of whack. other mods? injectors, maf, larger turbo... Have you changed the fuel filter?
 

WaRrIoRs16

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Mar 23, 2008
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373
Location
Ferndale, WA
The only other mods I have are 3G lifters and a K&N air filter. I don't remember my trims being like this before I installed the exhaust becuase I remember comparing my trims between my galant and my pos talon. I have not changed the fuel filter before and I'm on stock injectors.
 

SouthCaliVR4

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Jul 31, 2010
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North county San Diego
I'd try a filter first especially if it's been sitting, could be pretty crammed full o junk.
 

Faulty o2 sensor, exhaust leak. /ubbthreads/images/graemlins/dunno.gif
 

Brunoboy

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Apr 25, 2008
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Location
San Bruno,CA Home of SFO
Is everyone forgetting the possibility of boost creep? Are you watching your boost gauge for any signs of creep? I know for sure 3" tends to make cars creep thus more boost not enough fuel will lean out .
-shane
 

SouthCaliVR4

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North county San Diego
I hadn't thought of boost creep on a 14b, mine was dead prior to the 3" install so I have no first hand knowledge of whether or not it would be an issue but definitely something to consider.
 

WaRrIoRs16

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Mar 23, 2008
Messages
373
Location
Ferndale, WA
I dont see any boost creep, the needle holds steady at 12psi. I dont think I have any exhaust leaks, but I will definitely check that out. I dont know whether or not my o2 sensor is having issues, I replaced it two summers ago and it appears to cycle as it should. I just went down to the auto parts store and got a replacement fuel filter, so I'm going to try and put that in soon. I appreciate all of your replies.
 

3rdstrikedsm

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Feb 17, 2008
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Location
32159, FL
If you are on a stock fuel pump then there is your problem most likely.
 

WaRrIoRs16

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Mar 23, 2008
Messages
373
Location
Ferndale, WA
So are you saying that maybe the stock fuel pump is not functioning properly? Or that its just not a good enough pump.
 

Brunoboy

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San Bruno,CA Home of SFO
Not good enough
 

WaRrIoRs16

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Mar 23, 2008
Messages
373
Location
Ferndale, WA
Alright, I should have my fuel pump and adjustable regulator by the end of this week. I guess I will put those in and see if that fixes the problem, along with the new fuel filter. The pump is the Walbro HP 255 and I got a Fuelab adjustable fuel pressure regulator kit. The injectors shouldn't have any trouble keeping up if I stay at 12lbs of boost should they? I'm also going to investigate for exhaust leaks at and before the o2 sensor and check for vacuum/boost leaks.
 

SouthCaliVR4

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Jul 31, 2010
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North county San Diego
injectors will be fine @ that boost level. above 15 lbs you'll start tapping fuel cut, you'll know if you do its like hitting a brick wall, not at all subtle.

Oh, fuel cut is an ecu setting based on air flow, no mater how big an injector you run on stock mas & elctronics your gonna hit it.
 
Last edited:

NickDromez

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Jul 2, 2010
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165
Location
Berkeley, CA
since i didnt see anybody answer your initial question, i would like to answer. No, a 3" exhaust will not cause a lean AFR mixture. the exhaust is located after the engine, so you wont see any kind of rich/lean/any other kind of mixture in the engine
 

SouthCaliVR4

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^^^ OK, I'll bite, what other kind of mixture would there be. I'm hoping cake, something in a chocolate but pancakes would be good too /ubbthreads/images/graemlins/laugh.gif I do believe it had already been established that the exhaust was unlikely to be the source of his issue but thanks for the empirical answer on that one.
 

WaRrIoRs16

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Mar 23, 2008
Messages
373
Location
Ferndale, WA
I finally got a chance to go to a buddy's house 30 mins away to work on my car, as they don't allow servicing or working on your car where I live at now. I did find a vacuum leak between where the intake pipe connects to the MAS and seeing as I don't have another pipe to replace it, I went ahead and relocated the battery to where the stock pipe filter was and used a 1g intake pipe with an extension made of exhaust pipe because it was the only thing I could find to make it work for the time being. I didn't get a chance to put on the fuel filter, fuel pump, or the fuel pressure regulator, those will all be taken care of next time I get some free time from school to drive to my friend's place. I am already noticing my fuel trims are better after fixing that vacuum leak. My low trim sorta flucuates but hasn't gone over 125% and my mid and high trims are 127% and 125% respectively, so nothing is maxed out. Im pretty sure that I can get those trims a little closer to 100% after I replace those fuel parts and do a boost leak test to fix the leaks.

One thing I did notice though is that I'm now only vacuuming 15inHg instead of the previous 18inHg or 19inHg. I don't really know whats going on with that, but I think I'll worry about it after I find and fix any remaining leaks in the intake system. Thank you all for helping me.
 

Do you have a wideband and what does your afr's look like at idle, mid and wot?
Make sure you are not running too lean especially at wot.Excessive detonation
from running too lean will quickly kill your engine......
 

WaRrIoRs16

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Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
I dont have a wideband yet. I only have an Egt gauge at the moment. I can't really tell if I'm running too lean. The trims are no longer maxed out though. Before I fixed the intake pipe, at WOT my o2 volts would sit at like .7x, which I read was not normal and that it should be at or around .9 volts. Currently at WOT the volts are up to .8x
 

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