hello,

Some background,
I've got a 92 Firebird 3.1L, has about 130K miles on it.

Recently I took the car to get smogged, It failed.
Excessive CO readings at 2500rpm, no problem at idle.
So i did a tune up, I changed the O2 sensor, Oil, Plugs, Wires, Cap & rotor, and changed all the vacuum lines.
Two weeks later I took it to get smogged again and it actually failed worse than the first time. Same problem, too much CO at 2500rpm.

So I decided to let them run a diagnostic on it, I left my car and called them the next day. My car had passed smog with flying colors. Funny thing is that they hadn't changed anything. They just ran the smog test again to see what was failing and it passed. It didn't just pass, all the readings were well below the maximum.

I couldn't help but wonder what the problem was and how it magically fixed itself long enough to pass smog. My suspicion is that if I had to smog it again, it would continue to fail and I just got lucky that one time.

The car seems to run ok, no hesitation or anything like that. But I'm getting horrible gas mileage. Driving across town (maybe 5-6 miles round trip) I can watch my fuel guage change pretty significantly.

If you guys could shed any light on the situation I would be very appreciative.
Thanks.

 

sticky injector
sticky EGR
EGR not opening fully

 

The EGR won't cause a rich condition, so don't stress about that.

You need to know if you're actually entering closed loop. What temp t-stat are you running?

Check to see if you are entering CL operation by running the engine and grounding the ALDL connector like ou were checking codes. If the light is blinkning fast, then it's in Open Loop, if it's blinking about 1 per second, then it's closed loop and should be controlling fuel properly. That's where you should start. Finding out if the car is even entering closed loop is the first step to diagnosing a rich condition.

 

It's been a while since I changed the thermostat, But i remember getting one with a slightly lower operating temp than stock, I think it's 180.
As for checking closed loop, I have to plead ignorance.

"grounding the ALDL connector... checking to see if the light is blinking...."

What light, and where is this ALDL connector?

 

You know how to check for codes, right?

The ALDL Connector is the diagnostic connector on the right hand side of the underdash area on the driver's side of the car. Look down by the center console on the driver's side and you'll see a small black box with electrical connectors in it.

The TOp row all the way to the right is terminal "A", the one immediatly left of it is "B." Normall, when your Service Engine Soon(SES) Light comes on while you drive, you can shut the car off, turn the ignition key to the "on" position with the engine off, insert a paperclip or some other form of jumper between the 2 terminals and the SES light will blink out codes to you in sequence.

If you jumper the same two terminals while the engine is running, the light will blink and tell you if it's in closed loop, O2 sensor fuel control, or if it's in Open Loop, default fuel control. Fast blinking is Open loop, not where you need to be normally, and slow blinking is closed loop, there are no codes displayed in this mode, just slow or fast blinking.

Once you determine if you're in Closed or Open loop, you can tell if it's mostly rich or mostly lean in closed loop by seeing if the light is on longer than off, or vise-versa. On longer means that the system is rich and off means the system is lean.

What I'm saying you should do is get the engine warmed up, then jumper the terminals, even at idle you should be blinking slowly after about 5 minutes. Even if you're not, then you should rev the engine up to 2500 rpm and hold it there and see if it blinks slowly for an entire 45 seconds.

Hope this helps a little. Check it out and report back, I do have other ideas, but you have to be able to determine this first and foremost.

 

I checked it out. At first start up the SES light was blinking rapidly, then after a few minutes it began blinking slowly. So it seems that's ok. Anything else I should try?

 

Now, do the same thing, but hold it at 2500 rpm for a minute and see what happenes. ometimes what happens is that the O2 sensor gets cooked and stops working, Normally this doesn't happen, but a defective sensor will do it. They are designed to work in a certain range, but because of 'lax quality control, bad ones sneak out and you end up with a bum new one.

 

I started the car up this morning, teh SES light blinked rapidly and then after about 2 minutes the light slowed down. I waited a few more minutes and then I revved up the engine to 2500rpm, I held it there for about a minute. I didn't see any change in the SES light, it was still blinking slowly.
Oh and I take back what I say about the car running smoothly, rpm's don't jump around too much at idle, but the car doesn't sound as smooth as it should be.

 

It sounds like the closed loo[p system is working properly, so now you'll have to break out the Digital Multi-meter and start checking out the load sensor output voltages. Check the TPS and the MAP sensor voltages and makes sure they have a smooth output range. You'll have to use a vacuum pump/guage to check the MAP, so go ahead and get one of those, you'll use it more than once, so it's worth it.

 

Awsome thanks for this tech insite i really appritiate it, or however you spell it,.,. this should be a sticky at the top of the page., but its just my opinion

 

Sorry I haven't replied. I've been out of town.

I know how to check the tps, but was wondering what range of values I should be looking for. I've checked and there seems no one can agree. I think I saw it should be between .58 and 4.something. Also, is it ok to hold the engine at WOT while it's parked? Won't it redline?
Also how do I check the MAP sensor, Where and how do I acctually go about testing it, and what am I looking for?
Oh, yesterday I got the suddend impulse to clean my engine. I scrubbed it down, and let it sit for a few hours to dry before I turned it back on. But when I did turn it back on, I opened the hood to admire my work and I noticed the base of the EGR valve was still wet and it was bubbling. Seems like air is leaking out of there. Is this normal?
Thanks.

 

Well, its "normal", but it shouldnt, lol.

Almost every egr that has failed, has because a gasket blew.


Odds are its your engine, but dont forget other things factor into MPG. Alighnment, tires, weight of car, driving style, wheelbearings, etc.