I've got an 89 firebird v6. It's been running badly for the past couple days. The system shows a code 34, which is for the mass air flow sensor. I've replaced the main relay and could not find the burnoff relay I see people talking about in other posts (if the v6 even came with one). I've even replaced the MAF sensor itself and I'm still getting the code. I hooked up a multi meter and I'm getting 14.xx volts to it and the output varies anyone from 0.xx to 5.0 volts. I know it's supposed to vary but it's jumping rapidly up and down within half second intervals (which is as fast as my multimeter can read). Is it supposed to jump this much. I need to find out if I bought another bad sensor or is something else wrong. - thanks

 

Crall,

You V-6 uses a digital MAF, not an analog like the V-8 TPI engines. This means that the output of the MAF is not a linear analog signal (like 0-5V for 0-255 g/S flow), but a modulated frequency based on measured air flow. The output wave frequency varies in duty cycle, or the length of "ON" time versus "OFF" time. As airflow increases, the duty cycle is shortened, and the number output chages from "ON" to "OFF" (frequency) over a given time period increaes as a result. You are measuring a variation in voltage due to the fact that your meter is trying to determine a root/mean/square value of the output voltage, or average value. As the frequency increases, your meter is seeing the full 5VDC output more often, and tries to average (RMS) this signal into a votage reading. The more correct method to measure output is with a frequency counter, duty cycle meter (like an automotive dwell meter), or using the duty cycle scale on your DMM.

Chances are that the MAF output is correct for a given input air flow, provided the MAF hot wire sensing element is clean. If the burn off function is not working, the wire can get dirty. You can clean the wire by carefully spraying a plastic-safe carburetor/intake cleaner through the MAF - Again, carefully.

If the MAF output is correct, you need to check the TPS sensor for correct output at the idle position, and make sure the output voltage increases in a linear manner as throttle opening increases.

A '34' is the result of the MAF reporting an intake flow that is lower than the ECM expects, based on engine RPM and TPS information. RPM information is usually quite reliable, so make sure the TPS is adjusted and working properly.