vetteboyc5

iTrader: (9)

Im trying to diagnose If im having an exhaust leak issue causing my lean codes on my tuned 99 c5 with a MS4 cam and LT's

Ive replaced my intake gaskets to no avail, also added a known good mass airflow sensor.

Im beginning to wonder if my slip fits are causing the sensors on BOTH banks to see a lean condition. I have the rear O2's turned off

Im having an issue where the engine runs good(and particularly will actually idle without pedaling) if i reset all my fuel trims, after 100 miles It wont idle without pedaling, and it begins to dump fuel at idle you can litterally see the rich smoke and it makes your eyes water.'

If there was a way to fake the signal to something of a normal reading, The exhaust leak wouldnt matter at that given point(Keeping in mind this would be merely to diagnose the issue)

Im trying to difiniatively diagnose this before i sink money into trying to repair the real issue of the leaks at an exhaust shop.

Would rear 02 simulators work, with the adaper plugs (I already have them since in running my vette rears o2s)

Ideas?

ChrisS@sdpc

Don't believe the rear O2 simulator would work. I have never tried that, but the signal requirements for the rear O2's are not the same as the front O2's for the PCM. Besides, I believe the sims are a big no-no. I don't believe there is tool out there that will do what you are asking.

You indicate that the car is tuned. Are you doing the tuning? It sounds like you may have a tuning issue. You may also have a physical issue, but based on your description of the idle problem it sounds like there is still work to occur regarding the tune.

Are you getting P0171/P0174? Double check for any vacuum leaks. Any changes made to the car lately?

TAQuickness

iTrader: (28)

If memory serves, the MS4 has a little lump to it. A lumpy cam at idle misfire creating false lean conditions. Air leaks can cause the same problem.

You can check for air leaks on the intake side using starting fluid. When you find the leak the engine will change tone.

On the exuast side, I find a seafoam treatment to work wonders identifying leaks. White smoke will come out of the leaking areas.

Both leak checks can be done for less than $10.

If you're still getting the lean condition, I would suspect a tuning issue.

LS1-450

iTrader: (33)

Rish enough to see the smoke is trouble. What are your LTFT's @ idle? If they are 25%, then they are probably much higher than 25% because the software limits the displayed output to 25%. Have you added intake mods such as a high flow filter, lid, larger TB, fitler to intake tubing. Sounds like you need to increaese your MAF frequency table. You may also habe a leak before the front O2 sensors. Is one of the front O2 sensors reading a higher voltage than the other, if so, the leak is related to that side. The rears don't mean crap. Don't worry about the rears. Let us know the answers to these questions & we'll go from there.

jrocstar

iTrader: (31)

the other thing to look at is how long the exhaust is. I am assuming a good set of headers and if the exhaust ends shortly after you will be pulling fresh air in between cylinder firing causing a false lean condition. but like ls1-450 said it is probably your ve tables need tuning for the new rise in airflow. This would explain the resetting fuel trims and running like **** ms4 is a big cam you will need alot of work to make that run reliable

addicted2fun

Someone once told me throwing on o2 sims on the front is BAD juju because its not reading the proper numbers. I dont have any information other then that to back up anything i just said. Although in one of the stickies it does say in big red bold letters to NOT put on o2 sims on the front.

jrocstar

iTrader: (31)

a o2 sim produces a constant voltage much like a rear o2 should produce after exhaust gases have passed through a cat. A front o2 should have a sine wave kind of like peaky mountains up and down showing multiple cross counts. If you install a sim in the front you will get insufficent activity bank 1 and bank 2 along with insufficent cross counts codes causing your car to enter open loop

2002_Z28_Six_Speed

iTrader: (19)

If the car is tuned then you don't need 02 sensors.

vetteboyc5

iTrader: (9)

I had the car tuned at a FORUM sponser In Cumming GA.. Ill leave the name out for now.

Long story short- I built the motor (stock rebuild, with headers and cam and a weiand intake) I brought it to said tuner just after breakin(driving very easy) and had the car tuned.

Leaving the tuner it would idle,Once i got almost 100 miles home, The check engine light came on, I stoped at a gas station, It would no longer Idle on its own, and started dumping black smoke at idle from then on it wouldnt unless I reset the battery.

Codes were:

P0101 General Maf code
p0171 Bank 1 lean
p0174 Bank 2 Lean


From then on It would do the same thing after 100 miles. Tuner has blamed every componet under the sun.

First it was my Maf, I replaced that,
then my weiand intake, Replaced that with a LS6 with new gaskets.

I have double checked EVERYTHING. I went back to him and You could tell he didnt even want to look at my car, nor did he pull any data for me. I paid 600 dollars for this tune.

Would turning my 02s off(Running a OPEN loop ) tune maybe be right for me? like the last poster said? He tuned it If im not mistaken with a gas analizer..

It seems like once it goes through drive cycles, Its sensing a false lean condition Its adding fuel, it begins to not want to idle.

Im trying to be difiniative here,but I have no scanning equipment and im to scared to try tuning myself...Im sure id screw it up..

I think the guy did a poor job..

jimmyblue

iTrader: (11)

The shot-through air at idle fools the O2 sensors,
regardless. They read oxygen and the relation to
real air fuel ratio is embedded in the voltage
threshold, but becomes bogus with the big overlap.

What I recommend is, playing with the O2 sensor
switchpoint (threshold) voltages. You have to follow
a chain of tables, know what "airflow mode" cell(s)
you idle and cruise in, and for these you want to
push down the millivolt value until the gas analyzer
reading in closed loop is 14.7:1 (or slightly richer)
when the fuel trims have settled. Then having found
the magic millivolt numbers for where you try to run
in closed loop, you can tweak the airflow tables to
get the trims zeroed.

LS1-450

iTrader: (33)

Since you don't have tuning software, the car will have to go to a tuner to fix it. We need to know what is happening & when (in regards to the tune) in order to better help. Find either a forum member with tuning software or a different tuner. My feeling remains that a MAF frequency table adjustment is @ least part of the solution.

2002_Z28_Six_Speed

iTrader: (19)

Dang. Sorry to hear this! I am constantly hearing about bad tuners from posters on this forum. I do not understand why they are so prevalent and how they are making enough money to stay in business.

I hope it works out for you. My car was tuned myself and I came from ground zero with no tuning exp but some data aquisition + sending it off to a tuner. My car idles perfect in open loop. But it took work!

jimmyblue

iTrader: (11)

My concern would be that the wideband is as susceptible to
spoofing as the narrowbands. Maybe more or less so, but it is
still the same basic technology and the same basic embedded-
assumed-relation (exhaust residual oxygen to intake AFR) in
play, which high overlap and low RPM renders false.

Just because it's an imperfect tune doesn't make them a
"bad tuner". There's no such thing as perfect and there is
such a thing as money paid / shop rates = time spent. Only
one variable there and what gets done, gets done. Not to
say there aren't bad ones, but seems like every one has
both nut swingers and sooner or later, nut kickers.

This is why I don't tune for money and seldom for strangers.