I got this code about 5 months ago and replaced both my O2 and fuel filter and the car was fine. Just recently (in the past couple of weeks) my car would start randomly rough idling. A really bad sputter. Today on my way up to school I got the dreaded check engine light and it was code 44 lean O2 reading. I really don't think it’s the O2s again. I say this because when I did the O2s and the fuel filter before, the fuel filter was the original from 94' It was clogged pretty good. So I’m fairly sure that was the source of my problems before. Could I be having the same problem now???

Also, a friend told me that the lt-1 would run w/o the O2 sensors. He said that it would just run off of the MAF. He said the computer would auto calculate the O2 reading off the MAF reading. He said it was not very accurate but it would work. So I disconnected my O2s and drove it. NO CODE. I am completely lost. I thought if the computer was not reading anything from the O2, it would throw a code.
Any ideas of where to start? I really don't want to shell out the money for new O2 again.

How bad would it be to run w/o the O2s until I have time to get them replaced?

Sorry it’s so long...I tried to put as much detail as I could in.

Thanks, Jeff

 

on my 92, code 44 gets set when the sensor reading drops out (<200 mV) for 50 seconds while in closed loop operation. therefore, if you disconnect the sensor before starting up the engine the ECM just thinks the O2 sensor is not warm enough and will never go to closed loop. no codes should set as a result.

if you get the engine running and decently warm to induce closed loop operation, and THEN disconnect the sensor then you should get code 44.

your friend is right about the LT1 (or any engine for that matter) will run without O2's (but maybe not well). but no sensor that i know of will guesstimate an O2 sensor output based on MAF or any other sensor. perhaps your friend said the MAF is used to calculate the fuel pulse width in absence of the O2 and he would be right. the system just stays in open loop, and the O2 sensor is not used in the fuel calculation.

i think the only way to know for certain regarding the O2 being "good" is to get a scanner hooked up to your car to monitor the O2 output.

also keep in mind there may be something else that is fouling the sensor to make it go bad real quick. i'd check plugs to see if there are any cylinders running rich/lean.

 

If it were me I would replace the fuel filter first, 5 bucks isnt gonna break the bank. Then clear the code and give it a shot, then read the 02's if it doesnt clear. You can get a good reading just like you can off the plugs.

Check your fuel filler neck for signs of rust.

When you remove the fuel filter cover the inlet/outlet with your fingers and shake it up, then dump the contents from the inlet side in a clean container. You'll get a good look if its the cause of the lean condition.

 

Thanks for the advice. I'm going to replace the fuel filter this weekend and try that first. jd_vtt3 is right, $5 won't break the bank. So it’s worth a try if it is still bad...I’ll get the o2 scanned. When I pull the plugs what should I look for...I mean should I look for variations from cyl to cyl or just in general look and see what the plugs are saying. Could a clogged injector cause this? I do have 100k+ miles.

Just for piece of mind...open loop is where the car is not yet up to operating temp and the O2s aren’t warmed up enough to read and closed loop is where the O2 are helping calibrate the F/A mix? Right?

Also, that would explain why the car runs fine until it warms up. But wouldn't that be a sure fire way to tell if its the O2. I mean since it runs fine until warm. I guess the only sure fire way to scan it. But what's weird is that when it throws the code, it starts to run fine. Is that because the sensor is not putting out a reasonable reading and it is taken out of the F/A calibration?

On the topic of scanning it does anyone know if you have to buy the cable from datamaster for the software to work or can you buy them from another company? If so who has the most reasonably priced.

Thanks again,
Jeff

 

right.

once a code is active for a sensor, default values for that sensor are used. in the case of an O2 failure, it should cause the system to stay in open loop.

might want to search through C4 Scan and Tune.

good luck.

 

Alright...this weekend, I changed the fuel filter...didn't help. So, I built an interface as suggested in scan and tune and ran datamaster. It’s a bit overwhelming for not knowing that much about the computer on the car. But it was reading the left side as very lean and the right side as just a bit rich. It has a very rough idle when going into closed loop and after a while it threw code 44 and went back into open loop. The left O2 reads a very constant number the whole time. It started at about 250 and decreased to below 200mV then after a while below 200, it threw a code. The right O2 was very sporadic (isn't that how it’s supposed to read??). I pulled all of my plugs and the left side plugs looked extremely carbon fouled like the engine was running extremely rich. Since this didn't not match was datamaster said, I was thinking that maybe the spark was not completely burning the fuel and carbon fouled the plugs and the 02 wasn't getting a good reading...so, I replaced all of my plugs. I haven't had time to bring it back out to see if that fixed it but if it did, then its only temporary unless its something else in the ignition is bad. I don't see how 4 of 8 plugs all on the same side could just happen to go bad. Any other suggestions??? Coil??? Thanks

 

i don't know if the datamaster filters O2 sensor readings, but if you hook up an oscilloscope to the sensor the readings will fluctuate like you describe the right reading did. my guess is that the left O2 is already shot - it's probably so fouled that no gases are penetrating the sensor element. pull it out and take a look.

as for the fouled plugs, i don't have a good guess since you see an entire bank messed up. if it was one or two cylinders i would suspect leaky/failing injectors. hopefully someone will chime in.

it does seem like this rich condition is what is causing all of this.

 

Well, I don't know what to do, when I am home next week I will pull the O2 and take a look at it. But that is just a temporary fix. If anyone has any ideas let me know. If it will help I will email the datamaster file. I'm sure someone else could get a lot more info from it than me.

Also, I’m guessing because of the small left O2 reading, that’s why the injector pulse with is so large on the left bank. What sensors are used to determine the A/F mix in closed loop?

The only other thing I was thinking.... the coil or something in the ignition could be causing a weak spark fouling out the O2 then faking the ECM to thinking a lean condition thus accelerating the fouling to the point where the plugs and the O2s are the way they are. Just a thought.

Thanks again!

 

I had a code 45(o2 sensor) on my '91. (running rich). replaced 02 sensor near pre-cat. Code would not clear. Turns out 2 of the 8 injectors were not operating properly. I replaced all 8 w/24lb hr (new). Cleared code. Took for test drive, re-checked for codes. None. So, in my case it was the injectors. Hope this helps.

 

to name the big hitters - TPS, coolant temp, MAF, MAP, engine speed..., and of course the O2 sensors when in closed loop. if the sensor was incorrectly reading lean, but just enough to stay out of error range, the ECM will eventually learn this in and add more fuel than it should.

compare the left/right BLM's and see if they are way different to confirm this.

however, even if the BLM's were "perfect" (i.e. all 128) the ECM will add more fuel to the appropriate bank when lean, just as you said.

now that you are armed with a scan tool, check the O2 sensor and replace if it looks trashed. then using the scan tool see what the O2's read.