Running lean

My car has started running lean and I can't seem to figure out why. The BCS is retarding the timing as soon as I hit boost.

my mod list
3" down full exhaust
super 16G ported
550cc inj
255 walbro
ported head
3" intake
hard pipe IC
2G mas

It ran rich until about 3weeks ago, I pulled timing (jumped) and then I got it fixed... now it runs real lean..at least it smells lean. I dont know what the deal is everything is less than ayear old....

My datalogger gives me funny O2 readings... injectors seem to be working fine... I have a new O2 sensor...but I want to find out if that could be it... (cuz I cant take it back if I put it in)

how are you controlling your fuel?
stock narrow band o2's 99% unreliable to tune with?
what is your base timing and fuel pressure?
can you post a 3rd gear WOT 3-7k log?
ps. lean is good. better timing.

no I cant posta log, my comp wont accept the program to allow it.

no AFC...yet

People on tamparacing said I didnt need an AFC with a 2G mas and 550cc... WTF they couldnt be more worng...

I am starting to think my FPR may be bad....hmmm no fuel pressure readings... for you to see.

I am still leaning towards my O2 though...

Could my O2 make my ECU change fuel curves without throwing an error code? and by doing so causing detonation (by running lean) and making my car pull timing to compensate?

sorry i didnt see your post earlyer. tamparacing is wrong!! buy a safc-2, or dsmlink. your o2's are narrow, there not accurate. you CAN NOT tune off your stock o2's, you can buy a 300 wideband, and tune accuratly with that. i dont know what to tell you, without a log, i cant help much.

ok, let me re-phrase...what i am asking you is... is it possible that my O2 is not functioning properly and telling my ECU something I know is impossible...i.e running a 255lph walbro on 550s inj. and it says its lean... when I know that it SHOULD NOT... how do I know? I ran it for 4 months rich (I mean you could smell it,,,like raw fuel) *So I just changed my oil often and waited for an AFC*

so...when I know my setup is rich...then all of a sudden it starts to run lean...(like burning crayons) and get knock @ 2 psi... something had to have broken... either its my O2 or my FPR...right?

You seem to know way more than me... look at me as your student... I dying to know what you have to teach me....

probably your o2 sensor. raw gas in the exhaust is not good for your o2 sensor.

no I cant posta log, my comp wont accept the program to allow it.

no AFC...yet

People on tamparacing said I didnt need an AFC with a 2G mas and 550cc... WTF they couldnt be more worng...

I am starting to think my FPR may be bad....hmmm no fuel pressure readings... for you to see.

I am still leaning towards my O2 though...

Could my O2 make my ECU change fuel curves without throwing an error code? and by doing so causing detonation (by running lean) and making my car pull timing to compensate?


As for the computer, did you go to http://www.java.com and download the JRE (Java Runtime Environment)?? Go there and click on the "get it now" button. Install that and reboot, even though it doesn't ask you to. That should solve your computer problems.

As for the O2, you should be able to tell by the logger if your o2 is bad. It should be cycling back an forth at idle and under normal driving conditions. At WOT it should stay steady around 0.90v - 0.95v (provided you are tuned correctly).

Also, am I reading everything right....you don't have an SAFC-II? You need to have one to compensate for the 550cc injectors. Most guys also recommend an AFPR if you are running a 255lph fuel pump.

The ECU, by default, will always treat the car as if it has 450cc injectors. It does not know that you have upgraded.

But, in conclusion :biggrin:, you NEED to get an SAFC-II or some other means of fuel management. You also need to get the computer running so we can see the logs. Take a look at your STFT, LTFT and the 02 voltages you are getting from the logger and let us know.

Good Luck!

The troubles mount.. in effort to narrow my sypmtoms... I took apart my car... I see some scratch marks inside my turbo housing.... and a little oil in the IC pipe (lower) Im getting worried... I dont think my turbo is blown... it runs fine until I try to boost it... (Datalogger says !knock!) and it pulls the timing... if my turbo was bad... why the hell would it run lean? not only that would I hear it? It has been smoking a little lately... I have to figure this out!!!!

All right, I dont even know where to start in this thread. There are 20 things going on here that having little or nothing to do with each other ;)

I dont know what "I pulled timing (jumped)" means. Pulling timing refers to ignition timing, jumped timing refers to cam timing. Two unrelated items.

You can NOT tell a car is lean by the smell, especially at WOT in a 3rd gear pull, unless you can still get your nose behind the car. Time for a logger or something that give real data.

You say that by the logger the O2 seems fine, but you still suspect it. If it is cycling smoothly at idle and cruise it should be fine. What does it read at WOT and high rpm?

Lean is not good, if it makes you're motor look like mine ;)

How can you start to think your FPR is bad when you dont have a fuel pressure guage? ;)

The AFC and 550s nearly cancel each other out, but there is some non-linearity in the two curves. The 2g MAS reads 20% lower, the 550s need to be about 18% lower. Wether you drop that 18% by an AFC, or a 2g MAS, the end result is nearly the same. I Would still run an AFC though to fine tune it.

O2 readings are NOT used at full throttle. A bad O2 will not affect WOT performance.

Running a 255 with a stock reg will make you run quite rich at idle and cruise. Up until around 10 psi actually.

I dont know what "small scratches" in the turbo means, but a decent amount of oil is common in the piping from the intake onward. Either way, a bad turbo has nothing to do with AFR.


Moral of the story, any further discussion is just further speculation until we see a real log. ;) Not trying to be a dick, trying to help. If you can't get a log posted at least post some impression of what O2s are doing in a WOT gear pull, what timing is doing, etc. Turn the boost all the way down until this is sorted out. But make every effort possible to get an actual log posted please.

Finally... thank you for giving me peace (I knew I wasnt crazy) everything just went all at once (typical DSM)

first of all your not being a dick, youre just being *as a matter of fact-like*

Im glad to hear you have the ability to see that these problems are not related... everyone has been telling me my turbo-crankwalk-badrings-so on.. I dont think that is what it is...thats why I am here.

O2- it tells my ECU how much Oxygen is in the exhaust...and to adjust the fuel accordingly.
My car is running lean (white plugs) and I have a small bolt size hole that is under my drivers seat. I know how my car smells (I am at one with my machine) and it doesnt smell like it used to before I jumped timing. It smells HOT, and has been running hotter like 220.

Either it is my O2 telling my car to run leaner, or my FPR isnt working properly and giving me enough fuel. My fuel pump is 6 months old, as are the injectors, and the fluidyne radiator.

Ill get you the log (Im taking it out for a little run)

Thank you for your help..

BTW I have tough skin...and big ears.. *educate me*
I will do as you ask and get you log

if by jumped timing you mean your timing belt slipped then you need to fix that as soon as possible before it slips more and the valves hit the pistons. make sure to get the timing belt tensioner, balance shaft belt, and balance shaft belt tensioner changed too. im getting ready to redo the timing belt on my car since the guy i bought it from was too cheap to get a tensioner :screwy:

I think he already fixed the belt stuff. If it is off it can cause the motor to run hot among other problems. One thing that just occured to me is that if the intake cam is out of whack igition timing will be off, since timing is indexed to the intake cam (the CAS gets its position from the intake cam in all year DSMs). The exception would be 2Gs, I believe they get it from the crank sensor. Hmm, that may not explain anything then. I dont see any mention of what year this car is though (put it in the sig! :) )

The o2 sensor could be off, but it almost ALWAYS makes you run rich. And it has ZERO effect on wide open throttle running (WOT).

The log will help, bring it on :)