Cobra running lean at idle after a WOT pull

SVTdreamin04

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What are your mods? I viewed your profile and didn't find them. What type of fuel system are you running?


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SVTdreamin04

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If you are running a BAP with stock pumps, you could've partially blown a hose in the tank. Usually, they blow off completely, but maybe it has just ruptured.


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SvtCobra0404

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Let's verify fuel pressure. Did you put gas in the car right before these lean issues arises?


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Nope did not put gas in. Literally just parked it and over night the next day the gauge was going crazy from 17.0 to 15.5 then to 16.5. What should spec be for fuel pressure at idle? Should I check at idle and higher rpm?
 

SVTdreamin04

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Nope did not put gas in. Literally just parked it and over night the next day the gauge was going crazy from 17.0 to 15.5 then to 16.5. What should spec be for fuel pressure at idle? Should I check at idle and higher rpm?

Check at idle. I would stay out of the boost if you check under acceleration.

The issue is present at idle so let's start there.


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SvtCobra0404

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Check at idle. I would stay out of the boost if you check under acceleration.

The issue is present at idle so let's start there.


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So I checked fuel pressure at the rail and I checked vacuum as well. This is at cold start. Vacuum was 21 hg and fuel pressure was 29-30psi at idle
 

01yellercobra

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If it’s lean at idle would driving change anything?
I'm still not 100% convinced it's not your wideband. It might be the wideband itself. I would drive the car at part throttle and watch the pressure. It should go up as you accelerate. And watch your short term trims if you can.

21-22" of vacuum at idle is normal with stock cams. So you're good there. You said the car drives normally correct?
 

Rambro

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My car seems to be driving normal too. But put it in neutral and apply brakes to stop and sometimes it leans out to 16~17 then settles to 14.7~15.
 

SvtCobra0404

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Hey Guys

I know it’s been awhile. I ended up just storing the car for winter and now fired her back up.

so what I thought was happening was the MAF was a little oily so I thought it was throwing my readings off. I ended up getting a JLT catch can on the passenger side. Once everything was cleaned I started it up now. Cold start afr was reading 11.6-13.6 for about 10 seconds then it went to 14.8-15.4 @ idle. I gave it some boost not driving just at idle and it went down to 12.1. I know it’s still lean for boost. My wideband is located at the rear 02 but I do not have any cats. Please help!!
 

SvtCobra0404

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I also checked for exhaust leaks before front o2 and before wideband. Don’t feel any leaks. Don’t feel a vacuum leak as idle is target.
 

Corbic

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Is the car 100% stock? Are you running aftermarket injectors or tune?

May need to suck it up and just take it to a tuner.
 

SvtCobra0404

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Is the car 100% stock? Are you running aftermarket injectors or tune?

May need to suck it up and just take it to a tuner.

car has stock injectors & tune.

Mods are
JLT Intake
BBK XPipe off road
Borla Stingers.
I used a SCTX4 to turn off rear o2s.
My wideband is in the rear o2 on the driver side.
the only thing I don’t get is it always ran good with these mods until last summer when i started it the next day and it was showing lean.
 

01yellercobra

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You can't compare a free rev in the driveway to putting it under an actual load. I'm hoping you didn't rev it like that while the engine was cold.
 

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