lean and rich

TAKNDWN · Apr 7, 2011

Hey guys my car has been doing this weird thing where it will start running lean (above 17 AFR) and then get rich (around 10 AFR). When it gets lean it gets above what my wideband can read. When it gets rich it usually stays around 10 and i haven't seen it richer than that. But this doesn't happen at any specific time. It's completely random. Sometimes i can just put it in neutral and rev it a couple times and it goes back to normal. Sometimes it won't fix itself after i do this. Sorry for the sorta long post but i like details lol Any and all ideas are welcome. Thanks

Zach

Naptown_Stang · Apr 7, 2011

What sensors have you checked?

vermilion · Apr 7, 2011

what type of wide band are you using? first things first... what is the status of your plugs and wires? in the trifecta of combustion you need air, fuel, spark.. erratic spikes are usual cause of plugs fouling or blow out. hence check gapping and over all condition. next is wires and coil packs. how old are they and do they look shoddy or rust color? does it misfire? next on the list is coolant. are you leaking any coolant at all? most modulars leak some. gets in the #4 & #8 plug and lastly the valley of the block closest to the aluminum crossover.in the rear you have your heater system back there. this is where plugs get affected again... coolant leakage... get a fuel pressure gauge and check the psi at idle. should be between 32-40 psi and idle WOT but not redlining should be at 38 - 39. last but definitely not least and most important. what is the condition of your vacuum lines? are they routed correctly. do they leak/clogged. all these factors play with your air fuel ratio. having a REAL wideband that is sufficient is one of the best tools for your car. all of this can be checked in your driveway or street. please another thing to check is your intake gaskets. i use carb cleaner in areas around gasket surface to find leaks.

tools needed:
fuel gauge from parts store.
real wideband: fast, autometer, plx or not a narrow band light show.

TAKNDWN · Apr 7, 2011

Vermillion your awesome!! thank you for all of the information! its guys like you that i love this site. but anyways i checked all the wires and looked around the plugs. im gonna change the spark plugs this weekend. Ill check the gapping. i believe i saw the proper gapping on the hood sticker. the coil packs are good. they arent that old. i havent noticed a misfire but i wouldnt be surprised to have that on my hands soon. I looked around and saw no bad signs of any coolant leaking or vacuum leaks/clogs.Ill have to try and get my hands on a guel pressure gauge. I have an aem wideband and wired it up to my sct scanner so i can record some runs and check all that out. And also the intake seals and all possible areas of air leaking was checked very first.

Naptown what do you mean by that? Do you mean what codes i can read through my tuner. It tells me the normal codes for not having cats. But also have been having a theft code show up. cant remember the specific number right now. Could this have something to do with the problem??

Once again thanks for all the help! and sorry for the long posts :thumbsup:

ccasion14: :thumbsup:

the.greg · Apr 7, 2011

I am pretty sure that a true wideband can't be very accurate when just wired into a SCT tuner. I think a true wideband would require a downstream O2 sensor reading but I could be wrong?

vermilion · Apr 8, 2011

the o2s of the car are supposed to be accurate. however, i found that having a secondary wideband that doesnt rely on the stock computer gives a proper reading. i for instance have the FAST dual wideband meter. it was costly. http://www.summitracing.com/parts/FST-170402/ this instrument has let me accurately read how my stang is doing. i throw this info alot out there but it is bar-none helpful... actually the SCT is accurate also but if you datalog using the tuner to laptop you can get what your pcm interprets. using an analog meter with the SCT is also a good learning tool. many people have successfully used it.