'02 Impala 3.4L: Diagnose This!

impala
chevrolet

#21

you order new one or keep old one running, it might be a good idea to check if your car requires a “air/fuel ratio calibration”.
My Nissans have quite easy-to-follow procedure to have ECU to “learn” sensor readings after you replace it or have it cleaned. Unlikely it will be the same for your car, so try checking in dealer repair manuals, maybe you would be able to find one online


#22

Car still running fine. Just got over 500 miles to a tank, which is typical for this vehicle when it’s running good. But the MAF sensor continues to read ZERO during a data record with the Harbor Fake scan tool.

The computer must be using some default value in place of the MAF reading, right?


#23

Is the check engine light on?

Any current codes?


#24

db4690:

Well, yeah - the check engine light is ON with the MAF sensor code (P0102), but I expect to see that.

Noticed the Long Term Fuel Trim during the data logging was pegged at -14, which (I think) means the computer thinks there’s no air (or very little air), so it’s cutting back on the fuel.

If this is correct, I don’t see the downside here. No functional MAF sensor, less fuel being burned, no more hesitation or stalling (although that was likely more to do with the throttle body needing to be cleaned).

I don’t see any reason to replace the MAF sensor - other than to keep the Check Engine Light OFF, which has value, I suppose …


#25

Like I maybe said, the MAFs I’ve had that were bad ranged from hardly allowing the engine to run so you limp home at 10 mph to just having a rich reading on the on-board computer. I had two cars with the same engine so did a quick swap of the MAF to confirm before spending the $300 at that time for a new part. So if you don’t think the HF reader is just faulty, you may have a wiring or connection problem with the MAF.


#26

So your Impala is running great, getting excellent mpgs, even w/a completely defunct MAF? hmm … well, maybe count your blessings … lol … The check engine code for a faulty MAF and off the scale fuel trims are certainly consistent. The fuel trim off the scale like that wouldn’t necessary mean the engine is consuming too much fuel. It means the amount it is consuming is not consistent with the MAF reading. But the MAF reading is bogus, so the fuel trims are likewise bogus.

Maybe best not to look a gift-horse in the mouth. The O2 sensor is really all that is needed for general fuel metering purposes. It’s running well, keep on driving. Keep on the lookout for symptoms in the meantime. Problems I’d expect with a non-functional MAF would happen during changes in engine load, not so much when keeping at the same speed. So they might be

  • When you step on the accelerator hard, the engine might go lean & stumble briefly.
  • Backfiring when you let your foot off the gas
  • Periods of lean operation might cause some overheating
  • Rich operation might cause some spark plug fouling. Take a look at the tailpipe, see if you notice any soot forming there.

#27

Bing:

I’ve sprayed the MAF sensor twice now. It’s reading flat zero now, but if you notice the tables I posted above, it was pretty close to zero back then, too. I did check for power at the MAF plug and it was good (12 V), so I’m thinking the sensor is just shot. It does have over 200,000 miles on it now. I guess I could order that $60 Spectra from RockAuto that I’d been eyeing (just the sensor, no housing) to see if that corrects the ‘problem’.

GeorgeSanJose,

The fuel trim is “off the scale” negative, which I believe means the computer is decreasing the fuel pulse (and thereby using less fuel). I don’t think the fuel trims are bogus, I think they’re consistent with a computer input that shows little or no air intake.


#28

I don’t think we disagree, except for perhaps the semantics. What I’m saying is that since the fuel trim values reported by the scan tool are based in part on the air flow sensor reading, if the air flow sensor reading is inaccurate, the fuel trim values must be inaccurate too.


#29

So I just installed the new MAF sensor yesterday (Spectra entire metal housing w/sensor pre-sandwiched between), cleared the code, and drove it. Drove OK, but I didn’t have my Harbor Fake Data collector with me. So I just went out for a good highway drive with the Data Collector, and noticed the code was back: P0102, so I cleared it and started recording data. Three collections, including 2 @ highway speeds of ~70 mph, and the MAF is STILL reading ZERO! Double-checked the wiring and everything is connected.

First capture was Open Loop, but the next two were Closed Loop. Whereas my Long Term Fuel Trim was reading -14.1 before, now it reads -0.8 (capture #1), and -7.0 (capture #2). Capture #2 was taken at 72 mph and 1904 rpm, Capture #3 at 65 mph and 1780 rpm. The MAP was 10.0 (Capture #2) and 11.9 (Capture #3). SparkAdv was 42.0 (#2), and 27.0 (#3). IAT was 89 (#2) and 91 (#3).

O2B1S1 was 0.790 (#2) and 0.440 (#3). O2B1S2 was 0.470 (#2) and 0.475 (#mazda3

Any idea why the MAF is STILL reading zero? Got to be wiring, right? Air Filter isn’t “new”, but it looks clean, so I doubt it’s that…


#30

It appears you’ve corrected the fuel trim problem, right? Since the only change was the replacement of the MAF, and a long term fuel trim of 0.8 %, and the rest apparently within the +/- 10% range, the MAF must now be working. Why you get no reading on that parameter from it on your scan tool, no clue on that one. It may be that your ECM simply doesn’t provide that function. Suggest you ask a Chevy specialist shop to see if they can read out the MAF parameter with their Chevy scan tool.

If you are the scientific type you could rig up a bench-top cardboard air flow box using a vacuum cleaner and a variable angle baffle door to control the amount of flow, and install your MAF in the air path, wire it up, and see what the output voltage is and how it changes with flow rate. Wouldn’t work on some MAFs which use a digital output rather than an analog voltage.


#31

other than clearing code, did you anyhow calibrate your new MAF to your ECU/ECM?

from my experience, for Nissans, you have to make ECM to re-calibrate your air-flow or code will keep coming back, procedure is dead-simple, but unlikely it is the same for Chevy