Mass Airflow function on LLY

[Philsauto]

I'm trying to figure out exactly what the mass airflow sensor does for the Duramax motor, in this case it happens to be an LLY. I am getting black smoke under load and also have a reoccurring MAF code P0101. The data on the scan tool for the MAF looks fairly normal to me, though I don't have a lot of experience with watching the data stream on this vehicle (even though I own one of my own, and LB7 without EGR).

Is a faulty reading from the MAF likely to cause smoke? I have tried cleaning the hot wire unit with electronic cleaner, a trick that often works on gasoline motor hot-wire sensors and has worked on my own truck when I over-oiled the air filter. No luck on this one, though, and it as a stock factory AC Delco filter.

[Wink]

Heres what i have on MAF on a LLY
Has some control of fuel
used for EGR diagnostics to verify EGR flow
40 g/sec at idle
400 g/sec at WOT
Thats all i have . I haven't had to mess with one yet

[letsgo]

there are three 3 points to clean on the maf sensor 2wires each 1/4 inch long plus the resistor. that banks air filter does it have an oil impregnated filter????? if so you could be dousing the sensors with oil, which will screw up the maf. make sure that electronic cleaner you are using, doesnt have a silicon or non conducting oil, use alcohol only, sprayed from a hypodermic syring,

good luck drive safe

[Philsauto]

there are three 3 points to clean on the maf sensor 2wires each 1/4 inch long plus the resistor. that banks air filter does it have an oil impregnated filter????? if so you could be dousing the sensors with oil, which will screw up the maf. make sure that electronic cleaner you are using, doesnt have a silicon or non conducting oil, use alcohol only, sprayed from a hypodermic syring,

good luck drive safe

No, this one is bone stock. The grams per second is off, too high, and that is what is causing the code and I assume, the smoke. Unfortunately I still haven't figured it out. The poster above, Wink, says 40gps at idle. This one runs 55 to 60gps at idle, but the weird part is that my voltage readings are good at 1.35 volts, same as on my 2001 LB7, but the LB7 reads 44gps at the same voltage as this one reading 59gps. Makes no sense, like the computer has lost its ability to calculate, but I think that is highly unlikely.

[DmaxMaverick]

Shooting from the hip, here. The LLY should have a lower idle air volume, due to the EGR, at a comparative engine RPM. The LB7 (2001 CA only, and all other fed's) would be higher because of no EGR. Unless the idle is higher, the air volume should track very close. Doesn't make sense the voltage is the same, but shows different air volume. It makes sense it smokes, with a higher air volume reading. The input voltage will be static, but the output will determine the volume reading.

[Philsauto]

Shooting from the hip, here. The LLY should have a lower idle air volume, due to the EGR, at a comparative engine RPM. The LB7 (2001 CA only, and all other fed's) would be higher because of no EGR. Unless the idle is higher, the air volume should track very close. Doesn't make sense the voltage is the same, but shows different air volume. It makes sense it smokes, with a higher air volume reading. The input voltage will be static, but the output will determine the volume reading.

I agree, it doesn't make sense, but that is what it is. Sounds like a PCM gone stupid, doesn't it? The LB7 does not have a PID for Maf voltage, only GPS while the LLY has a PID for both voltage and GPS, but I am reading the voltage right at the wire on the two sensors and they read essentially the same.

You are correct on the EGR, however, the EGR is not energized on cold start, which is where I get the P0101. The GPS does drop once the PCM turns on EGR flow, but my code sets 17 seconds after engine start up. I have spent hours on this thing and I finally ended up soldering a 2k resistor between the MAF signal and ref low wires to pull the voltage down to 1.1 with the EGR off. This gives me a reading of 44 GPS and eliminates the code and reduces the smoke. I don't like it and I don't think it is a proper repair, but I was flat out of ideas besides replacing the PCM. Once EGR turns on, the GPS drops to about 30 at idle but so far, the computer is happy with that number.

[Philsauto]

Well, I thought I better post the fix. The computer was gone stupid, but only because of the wrong reflash. There are two flashes available, depending on the shape of the air cleaner housing. This early LLY has a square air filter just like my LB7 and the default calibration is for the round air filter housing. I started talking to the customer and found that the check engine lamp had come on after a reflash, a reflash that was performed in view of fixing a surging idle. But the idle problem was due to a bad fuel pressure regulator, and the dealer simply installed a second problem on top of the first one. It took me a long time to figure this thing out but it is finally fixed. I flashed it back to the square air cleaner housing calibration and the grams per second came right down to the correct numbers of about 40 gps with EGR off. No more MIL and no more black smoke. The voltage PID is still the same as before but not the gram per second calculation.

[DmaxMaverick]

That makes sense. Thanks for the update!

[Philsauto]

That makes sense. Thanks for the update!

I forgot to mention I removed my MM 2k resistor from the wiring loom. It had worked to keep the MIL off but was not a proper repair.

[DmaxMaverick]

I figured did. You'd be getting more codes or running issues if you didn't, now the math is correct.