PUREC4

Morning all. Still needing help. I replace defective Bosch MAF, broken wire. Replaced O2 sensor, and TPS. All have helped but still not right. Dies while driving, will restart, service engine light comes on and stays, instant MPG show 9mpg. Let stall retart light will go out and mpg jump to 19/22mpg in 6th at 70 mph. Will run fine for a while then do it all again. Engine seems to miss a little at crusing. New fuel filter. Also when stalling out at speed looks like it loads up some. Code I have found 21,22,45. One code set I think when directions had me place TPS on wrong. Fired off at about 1/2 .throttle. :eek: :eek: [IMG][/IMG] :eek: Any ideas, running out on my end. Running headers, 3" single pipe to Flowmasters. Could O2 sensor be having a problem reading. Flowmasters are new, too free flowing??
Thanks again ya'll.

dwestsr

Where is the O2 sensor located? If it is in the header collecter, the stock sensor may not be getting hot enough. It this is the case, you can get a heated sensor that will fix that problem. There is a tech tip on this I think. Good luck!! :cheers:

0ski_dwn_it

02s are the number one thing that cause people problems with their cars. Both in performance and fuel economy.

I wrote an in depth explination on how it work and why its sooo critical to the ECM to have the o2 reporting accurate readings.

I will try to dig it up. I WISH the mods would fix it as a sticky post at the top of the tech section as I think it would help many many people and would not get lost time and time again. I think something like that as a sticky would be much more valuable than group purchases.

Perhaps if enough people speak up we can get something like this done. It gets time consuming and annoying repeating the same VERY important things over and over again.

Let me see if can un-archieve the write-up. :rolleyes:

Found it: http://forums.corvetteforum.com/zerothread?id=674894

As I said, not because I wrote it, I think this would help MANY MANY people if they fully understood this concept and the importance of the 02 sensor.

Feel free to voice your opinions. :cheers:

Here is another: Written by Vader....this the IAC/Min idle & TPS that people have set wrong or neglected that causes problems. I can not stress how important it is to have these items work and correct to have a good running car. (unless your Hooked Up, sorry inside joke).
http://forums.corvetteforum.com/zerothread?id=621496

VERY VERY IMPORTANT STUFF!!!!!


:cheers:


[Modified by ski_dwn_it, 10:46 AM 1/21/2004]

C4Crazy787

Cut and Past of ski's O2 paper

02 Sensor Fuction and Testing 10-21-03
I have been talking with MANY people via email/phone/IM in regards to their setups. It seems that many of these people are experiencing roughly the same problems. Rough idles, poor gas milage, black smoke from the exhaust, ect.
These problems all seem to be linked to one common problem. Bad or lack of O2 sensors readings.
Once you understand how the ECM system works, you will realize that the 02 sensor is the #1 sensor that can make or break you.
Lets look at it in more detail. The ECM relies on feedback from the 02 sensor in order to correctly adjust fuel trims. This is a process that happens many times a second. The 02 monitors the exhaust gases and feeds the ECM information on the mixture. If the reading are lean, then the ECM will add fuel to the injectors trim to bring it to rich.
A key part of understanding how the system is suppose to work, is understanding what the 02 sensor telling the ECM with its readings.
A little information on the 02 sensor itself: The oxygen sensor itself is designed to generate a voltage based on the combustion mixture present in the exhaust system. To the 02 sensor itself the mixture this is either a rich mixture or a lean mixture. The o2 sensor was designed to be nothing more than a switch. Low readings less than .450 as said to be lean, greater than .450 volts are rich. The further from the .450 you get the richer or leaner a mixture is said to be. I like to think of .450 volts as a perfect mixture 14.7 AFR. Chemistry tells us that in order to combust 100% of an air & fuel mixture you need 14.7:1 ratio. That is 14.7 parts air to 1 part fuel. (different fuels will require different ratios, but this covers most of us here). When this mixture is achieved you have 100% combustion of the mixture. This is ideal for gas milage. If the mixture is said to be rich, you have not enough air and some of the fuel is left unburned. When your said to be lean, there is not enough fuel and air is passed through. The 02 sensor is calibrated to these different mixtures. As said above it reports these to the ECM, which adjusts it accordingly.
Onto what we all care about. Fuel milage, steady idles, quick throttle response, etc.
For emmission purposes cars are equipped with catalytic converters. To keep these converter happy, and allow them to do their magical chemical removal of harmful polutants they require frequent rich then lean spike in the exhaust stream. Understand that these spikes happen extremely quick several per second. The design of the algorithims of the ECM allow for this to happen.
The ECM is designed while in closed loop to toggle (switch) the Air/Fuel ratio from rich to lean. Tuners call this transitions. Transitions are reading from either side of the .450 voltage range. Follow me here. A GOOD healthy 02 will transition several times in a few seconds. ~15 times in 3-4 seconds. So in that 3-4 seconds. If one were to graph these values reported from the 02 you would see a very up and down spikey graph, with ~.450 as the average reading, or the midpoint of the high (rich) and low(lean) voltage readings. For all you mathmaticians out there, the midpoint or average would be .450, which we said earlier is ~14.7:1 AFR. In other words because the transitions happen sooooo quick and frequently, the resulting Air/fuel ration is basically 14.7:1. Which keeps the cats happy and gas milage optimum.
Ok, so let imagine what happens when a 02 is bad, wire rubbed through shorting the reading to the ECM, or is not getting hot enough? ( typical 02 MUST reach 650*F to operate correctly).
If your 02 sensor is bad then the ECM will take those readings for what they are worth. If they are stuck on the lean side of .450 volts, then the ECM is designed as I said before to add fuel to compensate the "lean" condition its being told. After it make a correction, it will add more fuel. See what is happening? There is no transition to rich. At some point, the ECM will quite its attempts, I do not know when this is. But what will result is a WAY WAY over mixture of fuel to air. Poor gas milage etc. Conversely, if its stuck on rich, the opposite will happen, fuel will be removed. Fortunately, as I said before, GM designed the ECM to recognize the fact that the transitions are not happening and to stop the trimming process to keep us from ruining our engines. However they did not incorporate a service engine light to tell us the sensor is dead. If you remove the sensor, it will trip a code, but I have never read/see a check engine light from a dead sensor. Wish they would have.
Another VERY common problem, has more to do with rough idle. Is the fact that many of us go with longtube headers, with ceramic coat. This causes another problem with the sensor. The sensor itself does not reach a hot enough temperature to properly work. That is why they make "heated" 02s. They are self heated to ensure that the 02 gets hot enough to properly function.
Enough of the "how it works stuff". How can you tell if your sensor is working? EASY and for 30 bucks you can monitor your 02s reading all the time.
Go to Wal-mart or equivalent store and buy a digital volt meter. Pick up some wire and some electrical connectors. This is about the easiest thing you will do to your car that will help you diagnose a problem. With the positive lead, connect it to your "information" wire off your 02 sensor. If you have a non-heated sensor, it will be the only wire on the sensor. Just get some of those connectors that allow you to side tap into wires. DO NOT CUT THE WIRE, the ECM still needs to get this signal too. Once you have the positive wire connected, then find a good ground for the negative lead. Any bolt will do on the frame/chassis. Make sure the wires are routed to the cabin of the car, and attach the volt meter to the leads. Set the scale of the meter to .xxx and start the car. After a short period of time you should see the Digital Volt Meter start to display random values. You should see while idling, values like ~.3XX then ~.7XX Then .2XX then .8XX then .2XX then .7XX.......you will think I lost my mind telling you to do this. But what you are seeing is exactly what the ECM is designed to do and what I said above. Its transitioning the mixture from lean (.3xx) to rich (.7xx) then back again. So you know everything is working properly.
If the reading is pretty steady with only small changes, then you have a problem. You should barely be able to keep up with reading the diplay and there should be large changes in the values, as shown in the paragraph above. If they are not acting like I say above, then put your foot on the gas peddle (Car in PARK) and give it some gas, to raise the RPMs about 1000. If then the sensor takes off and does as I say above, its just not getting hot enough. In which case you need to get a heated sensor (~50 bucks). What is happening is at idle the gasses of the exhaust are able to cool enough before hitting the o2, when you rev the motor the gasses speed up and reach the 02 quicker and at hotter temps. This is not a big deal, just get a heated sensor.
Ok, now you have the whole picture as to why a 02 is sooooooooo VERY VERY important to these cars. If its dead you throw the ECM into a blind scenerio where it can't adjust your fuel levels properly.
Wide open throttle is a whole nothing topic, so just keep your questions focused on idle/part throttle operation should you have any.
I SERIOUSLY hope that people will take the time to do this. Its VERY helpful to have this at your disposal. It will help you understand not only how the ECM is working, but as time passes and the sensor goes bad, you will be able to quickly detect it getting "lazy". The cost to do this is minimal, and with costs of fuel, will pay for itself in about 2 tanks of fuel. There is no excuse not to get this done. If you have a scanner you already can monitor what is happening. I have tuned two cars in the past month in person, and both of these cars had (1) a dead o2 sensor (2) the other had a lazy sensor at idle, but the latter of the two is not as serious. But still needs to be corrected.
If you would do the DVM trick, and see good transitions, and still be experiencing problems, its more than possible to have a short between where you tied into the 02s wire, and the ECM. If that happens one should then find the wire that goes into the ECM, from the 02 and connect into it right before the ECM as close as possible. If the reading are good close to the sensor, but bad near the ECM, you have a wire that is grounded out somewere between. In which case its probably easiest to just run a new wire to the o2 for the ECM to use. I seriously hope that people read this and do as I say. Especially if your having rough idles. Poor gas milage etc. Its will take about 1 hour to do and will like I said pay for itself in no time. Not to mention my hands from typing are killing me and I hope this wasn't all in vein.

Thank's ski, I read this and then saved on my harddrive.



[Modified by C4Crazy787, 10:46 AM 1/21/2004]

vinnies87

thanks, added to my tech papers.... good info... :thumbs:

CFI-EFI

Ski,
That is a great post. I agree it should be more readily accessable, but if all the good info is "sticky posted" at the top of the topic page, it'll become lost in the shuffle and we'll have to scroll down quite a ways, eventially, to get to new topics. I suggest you submit this as a "Tech Tip". That way it will be available to those that need, it at any time. Thanks, again, for the great post.

RACE ON!!!

PUREC4

O2 SENSOR IS LOCATED IN THE COLLECTOR, CAN IT BE SWITCHED TO A HEATED TYPE?

PUREC4

THANKS FOR ALL THE INFO, HAVE TO GO HOME AND SOAK IT ALL IN.
TWO OTHER THINGS, DOES IT MAKE A DIFFERENCE THAT I AM NOT RUNNING ANY CATS IN THE EXHAUST. ALSO CAN'T SEE HOW BUT ALL OF THIS STARTED AFTER A REAR END ACCIDENT, AND ADDING THE FLOWMASTERS AT THAT TIME, EVERYTHING ELSE IS THE SAME.
AGAIN THANKS FOR ALL THE HELP . :seeya

65Z01

You can use the ECM's field test mode described on my site (link in sig. below) to see if the ECM is going/staying closed loop.

If not, it could be a O2 sensor or the coolant temp sensor problem.

Since you have LT headers I too suggest you install a 3-wire heated O2 sensor. Since it doesn't draw much current (~250mA or less I believe) just tap into the power pin of the Fuel Pump relay with a 1A in-line fuse for power.

GusBustamanteJr

Follow the procedure in the Tech Tips, i did this weekend, and was happy with the results.

vinnies87

Vaders doc is a great tool.... :cheers: