Running Lean wtf!

M

Maz2001MP

Member
Contributor
As for my mods:

FMIC
MAF pressure side
intake
full CS exhaust
stock boost
stock ecu


For some reason when I'm cruising my afr's blip into the low 16's and the car bogs down a slightly and even hit a 17 once! The car sure doesn't feel like itself.

Also during WOT at full boost the afr's creep up to 11.3, the AFR's normally would stay pegged at 10.0!!!!! What the hell is going on? The car does feel like it has a loss in power and this all just started out of the blue yesterday.

Oh ya and vacuum is a solid 23 in., the idle is fine, cleaned the EGR about 1000 miles ago. No CEL at all.

I got a half a tank of 93 octane @ Citgo. I figured it might be bad gas so I finished the rest off at a different station (Mobil) drove around for a little tried to do some turns to mix the fuel but the problem still persists. Havent checked the plugs yet. Everything else seems to be normal.
 
Last edited:
try dropping your battery for about 5 minutes and then letting your car re-learn everything.
 
Bad o2 sensor? Do you have a wideband? If not, how are you reading your afr's?
 
Maz2001MP said:
As for my mods:

FMIC
MAF pressure side
intake
full CS exhaust
stock boost
stock ecu


For some reason when I'm cruising my afr's blip into the low 16's and the car bogs down a slightly and even hit a 17 once! The car sure doesn't feel like itself.

Also during WOT at full boost the afr's creep up to 11.3, the AFR's normally would stay pegged at 10.0!!!!! What the hell is going on? The car does feel like it has a loss in power and this all just started out of the blue yesterday.

Oh ya and vacuum is a solid 23 in., the idle is fine, cleaned the EGR about 1000 miles ago. No CEL at all.

I got a half a tank of 93 octane @ Citgo. I figured it might be bad gas so I finished the rest off at a different station (Mobil) drove around for a little tried to do some turns to mix the fuel but the problem still persists. Havent checked the plugs yet. Everything else seems to be normal.
Click to expand...


Yep, i agree, start by resetting the ECU and drive it around... see how all goes... if still issues you might have a faulty O2 sensor. The ecu uses the O2 sensor to correct fuel mixture t'ill around 3000 rpm or so. at WOT the ECU goes with predefined maps. So it does not take the O2 sensores info into account.

I have some hesitations and idle stales after warm up then it dissapears... but its the EGR valve and that will be replaced next week.

My O2 sensor and gauge goes from lean to rich constantly.... that is a good sign meaning the mixture is updated constantly.

let us know how all goes...
 
how much boost are you running?
i would think that having the maf on the pressure pipe in combination with running high enough boost would give bad enough readings to get you leaned out.
if the ecu runs pre defined maps you still might have the same issue.
you might get a AFC or turn the boost down assuming you are over stock.
 
exNeon said:
how much boost are you running?
i would think that having the maf on the pressure pipe in combination with running high enough boost would give bad enough readings to get you leaned out.
if the ecu runs pre defined maps you still might have the same issue.
you might get a AFC or turn the boost down assuming you are over stock.
Click to expand...

Stock boost as previously stated. I hope I just got bad gas though..
 
martyy2k said:
Yep, i agree, start by resetting the ECU and drive it around... see how all goes... if still issues you might have a faulty O2 sensor. The ecu uses the O2 sensor to correct fuel mixture t'ill around 3000 rpm or so. at WOT the ECU goes with predefined maps. So it does not take the O2 sensores info into account.

I have some hesitations and idle stales after warm up then it dissapears... but its the EGR valve and that will be replaced next week.

My O2 sensor and gauge goes from lean to rich constantly.... that is a good sign meaning the mixture is updated constantly.

let us know how all goes...
Click to expand...

Thanks for the reply. My wideband does the same thing at idle it will go between 14.5 and 15.1 sometimes but just recently after filling up my tank from Citgo after a few hours the car starting doing this.

The car has only 55,000 miles so I hope it isn't the O2 sensor. I think it might be bad gas.

I ran some Lucas injector cleaner just incase (even though I know people say it's useless). I also filled up my tank at a different gas station and I'm pulling the plugs today to check them and regap if necessary.

The issue has gotten better with the new gas though, as sparingly as it's been happening in the first place.
 
ItsSlow said:
Bad o2 sensor? Do you have a wideband? If not, how are you reading your afr's?
Click to expand...

"For some reason when I'm cruising my afr's blip into the low 16's and the car bogs down a slightly and even hit a 17 once! The car sure doesn't feel like itself.

Also during WOT at full boost the afr's creep up to 11.3, the AFR's normally would stay pegged at 10.0!!!!! What the hell is going on? The car does feel like it has a loss in power and this all just started out of the blue yesterday."

My AFR's at WOT have gotten better though now at redline im @ mid-high tens!
 
update:

Pulled the plugs and they look fine. I'm taking the car down to Atlantic City today, hopefully there won't be any Zoom Zoom Boom. I will also be resetting the ECU soon.
 
If it's getting better maybe it was just bad gas and when you added some more it mixed to ok. I'd try reseting the ECU, it only takes a 10mm and a few minutes or a scanner.
 
Yuppies i don't know what the hell you guys are talking about "afr's" and such but i do know that i have the same problem. Diagnostic computers says im running lean. The reading was comming from the front O2 sensor. Well figured the O2 sensor needed to be replaced so i replaced it. Still gots the same problem "running lean" w/the same reading comming from the front O2 sensor. Maybe the fuel injectors??? EGR valve??? by the way whats the EGR??? Vacumm???? Hmm so many things could be wrong. What to check first?
 
are iridium plugs recommended for N/A applications? (newb question of the month). i always thought they were colder and usually meant to be gapped for turbo apps.
 
Ok so I reset the ECU and drove for a good 6 hours over the past few days and the car seems much better now. The power is back and the lean spikes went away. The plugs are still fine. If anything else arises or the problem persists, I will test the Primary O2. Thanks everyone!!!
 
1moreMPH said:
are iridium plugs recommended for N/A applications? (newb question of the month). i always thought they were colder and usually meant to be gapped for turbo apps.
Click to expand...

I think TheMan has a thread regarding NA plugs. I am pretty sure he speaks of using the 5 heat range plugs but not the OEM plugs. I think the plugs he was talking about were ZR5FR or something similar (can't remember the name)...

Generally the Iridiums seem to run colder ranges from what I've seen but on an NA app you would usually want the hotter plug (not too hot though)
 
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