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Car running lean issue

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bigal07

15+ Year Contributor
93
1
Aug 2, 2007
Fort Dodge, Iowa
I just recently installed a bunch of mods on my car, evo 3 16g, boost controller, 3 inch exhaust, greddy 24v front mount, walbro 255, and i got a air fuel gauge, and when im just cruising at 60 mph its half way lean all the time, and another part that isnt good is that when i let off the throttle it shoots flames out the muffler, im running 12 lbs of boost, what could be the problem, im planning on getting dsmlink soon.
 
what you have done to the car is a good start, and i see that you upgraded the fuel pump, but that doesn't mean that the injectors can handle all that air flow. adding air goes hand in hand with adding fuel. widebands are great yes, but the A/F gauge isn't much behind it in accuracy.
 
bigal07 said:
I just recently installed a bunch of mods on my car, evo 3 16g, boost controller, 3 inch exhaust, greddy 24v front mount, walbro 255, I have a air fuel gauge, and I'm running 12 lbs of boost.

When I'm just cruising at 60 mph its half way lean all the time.
When I let off the throttle it shoots flames out the muffler.

What could be the problem?

At 60 mph cruising, steady throttle the ECU should be in closed loop mode and the O2 sensor output should be swinging back and forth on your air fuel gauge just like it should at idle.

When you let off the throttle the Idle Position Switch should close, the BOV should open and depending on the conditions the ECU should turn off the injectors to same fuel during deceleration. Shooting flames out the tailpipe is a sign of running rich and perhaps not having a cat and venting the BOV to ATM.

I don't see a aftermarket fuel pressure regulator in your list and that can cause you to run rich when using a 255 l/h fuel pump.

Did you pressure test the intake after you put the front mount on?

Do you have any logs?
 
Thanks for the info steve, to the possible flames, yes i am running no cat and vented bov to the atmoshere, it didnt shoot flames until i put the front mount and boost controller on.

The a/f guage doesnt jump around like you said, i have a friend with the same one that does exactly what u say although mine just stays at half lean.

What would be the easiest way to pressure test the intake?

Also i dont have logs right now, im going to get dsmlink once i get the money..
 
Sounds like the o2 is not cycling and you may need a new one. It should bounce around untill your wot. The bov not being recirculated can cause you to run rich between shifts and hence the blames out the exhaust between shifts.
 
well the a/f gauge will bounce around a little but not while at a steady speed, just when downshifting or revving, could i use a universal o2 sensor to replace the o2 sensor on the o2 housing?
 
bigal07 said:
Could i use a universal o2 sensor to replace the o2 sensor on the o2 housing?
Just order the OEM replacement. To many people blow out ECU traces by miswiring the universals and the cost difference is about $2. The Denso 234-4026 front O2 is about $48 from places like sparkplugs.com

Check the VFAQ or search here for boost leak testing.

You also need to recirculate the BOV.
 
Ok, i can get a new o2 sensor then, i was just wondering because i bought what was supposed to be a oem rear o2 sensor but a week later when i went to put it in the wire harness wasnt right, and my room mate threw away the receipt haha, but anyways i'll do everything you said and see how it goes, thanks a lot.
 
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