Anyone have any in depth insight on the following codes? Thanks in advance.

# 23 manifold air temp.

# 48 mass air flow.

Without having them professionally diagnosed, I'm planning to replace the MAF and the Air Intake Temperature Sensor.

I'm also planning to replace both of my O2 sensors. Will the O2's always throw a code if they're bad? I read that it's recommended they be replaced at 100K miles and my car has about that many on it. I've been through 3 cats. The first one collapsed at ~ 26K, the 2nd at ~ 76K and the third at ~ 104K, prompting me to ultimately put my car in storage. I'm guessing the cat issues may be due to a rich air/fuel mixture, but that's no more than an educated guess. When I recently pulled it out of storage and finally got it running it's missing and backfiring really bad under load. I'm thinking the Opti may also be bad, but I want to replace some cheap stuff first and see what happens.

 

Besides the obvious (sensor is present and accounted for, hooked up, wiring isn't damaged, etc.) I do not know of any specific test procedures for those two sensors. For the air temp sensor, the factory service manual may have a procedure where you can get the sensor to a specific temperature and measure the resistance. For the MAF, you would need to be able to simulate air flow through the sensor under a controlled environment and measure the frequency coming from it.

Regarding O2 sensors, I have heard they can fail in as little as 35,000 miles. Generally, the PCM can detect a malfunctioning O2 sensor by monitoring its "switch rate" and whether its reporting any voltage back. With over 100,000 miles, it might not be a bad idea to replace them but I wouldn't hold my hopes too high that replacing them will make your car run better.

Regarding the cats, that's pretty weird. They don't usually fail unless, as you said, the engine isn't running properly.

I doubt the backfiring is caused by the opti (otherwise the engine would run rough all the time, not just under load). Sounds like you have some other issues to track down. Hope this helps.

 

I actually received some factory service manuals this evening that I had purchased on EBay. I'm sure there is more info in those things than I'll ever be able to use, but it's pretty interesting digging through them. There appear to be documented procedures for diagnosing every one of the ODBC trouble codes.

My car has been in storage for over six years. If you're interested in reading some of the history, there is a pretty lengthy post here.

It looks like I'm not even sure how many cats I've put on it. Maybe I've only replaced two. I have it all written down with my car, but it's in Kentucky & I'm in Michigan.

 

I had similar problems with the fuel injectors on my Impala. When I tore the car apart to do the engine rebuild, i had the fuel injectors professionally cleaned. After I fired it up, I found at least two of them weren't working well. I replaced them all with Ford SVO injectors (shh don't tell anybody!). ;-) The guy who originally cleaned them said they do not like to be exposed to the air, even after they are cleaned. This is because moisture from the air can get in them and seize them up.

Given that virtually every component in the fuel system in your car needed to be replaced (injectors, fuel pump), likely due to the fuel gumming everything up, I'd suggest checking the operation of the fuel pressure regulator. The fuel pressure regulator takes a vacuum source from the intake manifold, and as manifold vacuum decreases (e.g. throttle increases), it's supposed to raise the fuel pressure. If it did not, your engine would suddenly go very lean when you get on the gas, causing backfiring, missing, etc.

Check your service manual for the testing procedure for the fuel pressure regulator. It's pretty straightforward.

In your other post you were asking about the MAF causing problems. Under normal conditions, the MAF is used in conjunction with the MAP to calculate fuel requirements based on airflow. If the MAF fails, the engine will still run in "speed density" mode, where the air flow is estimated based on manifold pressure and air temperature.

So, with the MAF trouble code, it is very likely the PCM has stopped using the MAF to calculate air flow and is instead using the "speed density" mode.