Have been getting a code 44, Lean Exhaust Indicated. SES light would come on if I was idling at a light but then go out when I was up to about 40 mph for a while and possibly back on again if I hit another light, (this became a usual pattern). Recently replaced the fuel filter and the fuel injectors (re-manufactured Bosch III injectors) but not the fuel pressure regulator on my stock 1990 L98 with 120k miles. Replaced the fuel pump assembly about a year and a half ago because fuel gauge in car was not indicating correctly. Car is now idling a little faster and seems to be running better however I'm still getting the code 44 and the light seems to be staying on longer or not going out at all, (it's never on at start up). I put a fuel pressure gauge on the fuel rail. Gauge read 46 psi initially then down to about 40 psi when the pump stopped. Started the engine and gauge read about 34-36 psi but the needle was fluttering and not steady,(I'll try to attach a short video of the gauge with car running). Could this be a bad regulator or a fuel pump issue?

 

I had a code 44 due to a faulty O2 sensor. My engine was actually running rich.

 

How old is the O2 sensor? I toss them every 5 years especially if they regulate the fuel air mixture.

 

I forgot to mention that the O2 sensor was changed last year when I had to have theY pipe and cat replaced. Car has original headers and MagnaFlow exhaust the rest of the way back. New exhaust is 2 1/2 in. diameter. Would that cause any back pressure issues?

 

Replace with 4 wire O2 sensor - after moving O2 downstream. I sell relocation kit but prefer you buy elsewhere !!

 

Your "New" O2 sensor is probably bad as well, they have a tough job to do and frequently people wait way too long to replace them. This is not a place to try and save money on budget brands, I use whatever the manufacturer used in it. I have purchased new O2 sensors from a popular mail order car parts place and received a faulty "Brand New" Bosch O2 sensor out of an order for four new O2's. I ended up eating the cost as they were sure I did something to it and it was an "Electrical part".

I agree with Aklim about regularly replacing them. I replace mine every 50 k miles or every 3-5 years depending on the car and how much it is used. I have one in my C3 that is there simply to monitor my carburetors ability to keep the car running properly. That one will be used as long as I can as it is an expensive one.

When they start to get old they can lag behind on their voltages which causes all kinds of problems for the engine. At that point the car is getting old data for new conditions. The voltage is between .1 and .9 volts and oscillates very quickly back and forth. Since the output of this one sensor carries so much weight in the air-fuel calculations I happily replace them before they wear out. When they get older the O2 sensors can actually start letting your car go into Open Loop while sitting at a stop light for an extended light. If you have a doubt about the O2 sensor then replace it with a known good one.

You need to be careful about putting certain additives in your Car equipped with an O2 sensor. There are additives that can poison the O2 sensor like some Octane Boosters and types of RTV. I always check the label if I am not sure.

Best regards,
Chris

P.S. Blowerworks suggestion of switching to a heated 4 wire O2 make a lot of sense and is a great upgrade over what our cars came with!

 

Thanks, but what does this mean and how do I fix it? Is it a bad sensor? I don't have a scan tool but imagine I will need one to interpret BLMs. I'll assume for now the new O2 sensor is good and the new injectors are working properly. I didn't replace the fuel regulator but with gauge on the rail pressure reads 46 psi with pump on and about 40 psi when it shuts off. Gauge reads about 36 psi when car is running. Would a scan tool pin point the problem?

 

I had a TPS that was faulty ie at closed throttle it read 39% open. The results was the car ran rich this eventually cause the o2 sensor to fail . The o2 sensor then reported a lean condition prompting the ECM to supply even more fuel.
You need a scanner to get the complete picture.

 

You will need one to see what the ECM is seeing and not what you think is the problem based on a code which you may not get as long as the value is plausible. Say the intake air temperature reads 10 below, it is plausible but not out of the window.

 

How does it work? Last time I saw it on the scanner, it moved pretty fast up and down so Would it be easier to just buy a scanner and actually see what it is doing?