Smog check and CHECK ENGINE LIGHT - Tilted Forum Project Discussion Community

Gatecrasher · 09-28-2003, 09:52 PM

1996 Ford Thunderbird, V8 4.6L
104,000 miles

My car didn't pass the Smog Check because the Check Engine Light (CEL) was on, showing OBD codes PO 172 and PO 175 meanng "System Too Rich (Bank 1) and (Bank 2)". Car runs perfect, and passed the emissions test.. but the damn light failed me!!!!!

Around 8 months ago, I went to the mechanic after my Check Engine Light had turned on, and he did a diagnostic, turned off the CEL, and said "nothing's wrong, don't worry about it". I know that the CEL can turn on for something as simple as a gast tank cap that is not screwed in tight enough.

The CEL can manually be turned off if you disconnect the car battery for minutes. And I guess that if it is a "real" problem, it will turn back on. (That seems to be the recommended advice to double check if the problem is real, or if it is just the CEL being annoying).

MY QUESTIONS:

So now I have to fix the "problem" and then go to get retested. Should I manually turn off the CEL to see if it comes back on? Does the fact that I turned it off light that considered "tampering" with my SMOG check? Would the SMOG test person see that? After how much driving does the CEL come back on, if the problem is really there?

Or, if "system too rich" is in indeed an ongoing problem in my car... how much will it cost me to fix? (estimate?) and/or is there anything I can double check myself?

Thanks

Peryn · 09-28-2003, 10:23 PM

eeyy....there are a number of things that could be wrong. System too rich means that you are either putting too much fuel into teh engine, or not getting enough air into the engine for how much fuel is there. You may have passed the test but by how much? That means the computer will automatically give it less fuel, and you will run on the right amount, or toolittle if there is an error. Your car could run hotter, less powerfull and have an increase in the NOx emissions.

A few questions for you. How long did it take for this CEL to get thrown after getting reset? If you reset it yourself, or just before the test, how far can you go before it gets thrown? If you reset an engine light they will not know. Unless it gets thrown frequently enough to show up while its on the dyno. If the problem exists it will show up reasonably fast. If it hasn't shown up in a couple days of driving, both hard and easy driving, long and short trips, then you will probably be OK. You might want to have your mechanic look at teh Oxygen sensors. One of those could be causing your problem. It could also be a leaky injector, plugged/clogged air filter, in a extremely rare case as bad as a flatened lobe on your cam.

Go have a mechanic check the O2 sensor and see how long it takes for the CEL to come back on. Chances are, your sensor(s) are bad or you can get away with turning off the code and resmogging it. If you do turn of the code long enough for smog, you will still want to fix whatever the problem is, as it could have more serious problems later on. Sorry if im blabbing, im tired. ill check back in teh morning.

m5man · 09-29-2003, 09:36 PM

O2 sensors should be replaced at 100,000 mi. because they get deposits on them just like spark plugs do. A dirty air filter or a bad AFM can also cause this. Also, your temp sensor can be out of spec causing the engine to think it is colder than normal and inject too much fuel.

Gatecrasher · 09-29-2003, 10:30 PM

thanks guys.

i went and paid my registration fees today, and got a 2 month extension for the smog check.. so i will be able to go through the elimination process to try to figure out the problem.

reconmike · 10-02-2003, 05:33 PM

Quick theory on ox sensors and running rich,
The o2's should switch from rich to lean 10 times in 10 seconds,
when the copmuter sees it rich it cuts down the injector pulse with, then it still doesnt see the o2's dropping lean so it cuts more pulse width.
It can only cut so much pulse width and when that happens then it turns on the CEL.

Check fuel pressure, even though the comp. is cutting down pulse there is still too much fuel passing through the injectors.

Leave the fuel pressure gauge attached and shut off the car, if prussure drop rapidly then you have a leaking injector.

You might just have 2 lazy o2 sensors, stuck rich.

If you reset the CEL and the sensors havent passed the readyness functions yet inspection will know that you reset it, here in Jersey if they are not ready the car still fails without the light being on.

OBD2 computers need atleast 2 driving cycles to reset a code and ready up the system.

2 drive cycles= car at normal operating temp, cruise at over 40mph for 2 minutes.

I hope this helps, if you have any other questions feel free to pm me.

Lyaec123 · 10-03-2003, 10:25 AM

Your 02 sensors are probably going flaky, just reset the computer right before you go to get tested and have it done. Won't hurt anything, other than the fact that you will get crappy gas mileage. If you want to fix the problem go to checker/kragen/napa and get a new set of 02 sensors for like $60 each and screw them in... the old ones look like little towers sticking out of the exhaust tubing after the manifolds. Bank 1 is probably drivers side, and bank two is passenger. If you are getting a rich condition, it will probably be the downstream (after the cat) sensors that are failing, but check the codes to make sure which one it is, and replace any as necessary. Good luck.

09-28-2003, 09:52 PM	#1 (permalink)
Gatecrasher Tilted Location: 213	Smog check and CHECK ENGINE LIGHT 1996 Ford Thunderbird, V8 4.6L 104,000 miles My car didn't pass the Smog Check because the Check Engine Light (CEL) was on, showing OBD codes PO 172 and PO 175 meanng "System Too Rich (Bank 1) and (Bank 2)". Car runs perfect, and passed the emissions test.. but the damn light failed me!!!!! Around 8 months ago, I went to the mechanic after my Check Engine Light had turned on, and he did a diagnostic, turned off the CEL, and said "nothing's wrong, don't worry about it". I know that the CEL can turn on for something as simple as a gast tank cap that is not screwed in tight enough. The CEL can manually be turned off if you disconnect the car battery for minutes. And I guess that if it is a "real" problem, it will turn back on. (That seems to be the recommended advice to double check if the problem is real, or if it is just the CEL being annoying). MY QUESTIONS: So now I have to fix the "problem" and then go to get retested. Should I manually turn off the CEL to see if it comes back on? Does the fact that I turned it off light that considered "tampering" with my SMOG check? Would the SMOG test person see that? After how much driving does the CEL come back on, if the problem is really there? Or, if "system too rich" is in indeed an ongoing problem in my car... how much will it cost me to fix? (estimate?) and/or is there anything I can double check myself? Thanks

09-28-2003, 10:23 PM	#2 (permalink)
Peryn Junkie Location: San Diego, CA.	eeyy....there are a number of things that could be wrong. System too rich means that you are either putting too much fuel into teh engine, or not getting enough air into the engine for how much fuel is there. You may have passed the test but by how much? That means the computer will automatically give it less fuel, and you will run on the right amount, or toolittle if there is an error. Your car could run hotter, less powerfull and have an increase in the NOx emissions. A few questions for you. How long did it take for this CEL to get thrown after getting reset? If you reset it yourself, or just before the test, how far can you go before it gets thrown? If you reset an engine light they will not know. Unless it gets thrown frequently enough to show up while its on the dyno. If the problem exists it will show up reasonably fast. If it hasn't shown up in a couple days of driving, both hard and easy driving, long and short trips, then you will probably be OK. You might want to have your mechanic look at teh Oxygen sensors. One of those could be causing your problem. It could also be a leaky injector, plugged/clogged air filter, in a extremely rare case as bad as a flatened lobe on your cam. Go have a mechanic check the O2 sensor and see how long it takes for the CEL to come back on. Chances are, your sensor(s) are bad or you can get away with turning off the code and resmogging it. If you do turn of the code long enough for smog, you will still want to fix whatever the problem is, as it could have more serious problems later on. Sorry if im blabbing, im tired. ill check back in teh morning. __________________ Dont cry kid, It's not your fault you suck.

10-02-2003, 05:33 PM	#5 (permalink)
reconmike Thank You Jesus Location: Twilight Zone	Quick theory on ox sensors and running rich, The o2's should switch from rich to lean 10 times in 10 seconds, when the copmuter sees it rich it cuts down the injector pulse with, then it still doesnt see the o2's dropping lean so it cuts more pulse width. It can only cut so much pulse width and when that happens then it turns on the CEL. Check fuel pressure, even though the comp. is cutting down pulse there is still too much fuel passing through the injectors. Leave the fuel pressure gauge attached and shut off the car, if prussure drop rapidly then you have a leaking injector. You might just have 2 lazy o2 sensors, stuck rich. If you reset the CEL and the sensors havent passed the readyness functions yet inspection will know that you reset it, here in Jersey if they are not ready the car still fails without the light being on. OBD2 computers need atleast 2 driving cycles to reset a code and ready up the system. 2 drive cycles= car at normal operating temp, cruise at over 40mph for 2 minutes. I hope this helps, if you have any other questions feel free to pm me. __________________ Where is Darwin when ya need him?

09-29-2003, 09:36 PM	#3 (permalink)
m5man Tilted	O2 sensors should be replaced at 100,000 mi. because they get deposits on them just like spark plugs do. A dirty air filter or a bad AFM can also cause this. Also, your temp sensor can be out of spec causing the engine to think it is colder than normal and inject too much fuel.

09-29-2003, 10:30 PM	#4 (permalink)
Gatecrasher Tilted Location: 213	thanks guys. i went and paid my registration fees today, and got a 2 month extension for the smog check.. so i will be able to go through the elimination process to try to figure out the problem.

10-03-2003, 10:25 AM	#6 (permalink)
Lyaec123 Crazy	Your 02 sensors are probably going flaky, just reset the computer right before you go to get tested and have it done. Won't hurt anything, other than the fact that you will get crappy gas mileage. If you want to fix the problem go to checker/kragen/napa and get a new set of 02 sensors for like $60 each and screw them in... the old ones look like little towers sticking out of the exhaust tubing after the manifolds. Bank 1 is probably drivers side, and bank two is passenger. If you are getting a rich condition, it will probably be the downstream (after the cat) sensors that are failing, but check the codes to make sure which one it is, and replace any as necessary. Good luck.