Mass Air Flow testing ambiguity

[Ivan80]

Last night while I was replacing the plugs, wires, cap, rotor, and both O2 sensors, I decided to test my Mass Air Flow sensor per the FSM.

I'm doing all of this because of a 11MPG average, an a stock truck with 33s. I'm also chasing a P0401 that's popped up twice now in 4 months - but doubt that's the culprit of the MPG. I have a rough idle at around 800 RPM (searched this, seems common, though I doubt they came new like this).

Back to the MAF question...
Bench test results on the MAF look ok, per the FSM, but it's instructions are too ambiguous to tell if it's truly good or not.

At about 75*F I was getting 2023 Ohms -which is within spec.
Then it says to blow air into the hole on the MAF, which I did, and it did indeed change the OHM readings, but only by 8 or so ohms (to 2015).

When I blew my own 96.8* air into the hole, the ohms fluxed the opposite way (to 2033).

Those Ohm fluctuations seem more indicative of a temp change from the colder or warmer air than the actual air flow into the MAF.
The FSM says if the Ohms fluctuate, the MAF is ok. That doesn't seem like enough flux, given the amount of air I was blowing into it. Only an 8 ohm change with about 40 PSI blowing into it?

Does anybody have a known good MAF they can test, or any experience on what should be seen here?

 

[SUMOTOY]

Does anybody have a known good MAF they can test, or any experience on what should be seen here?

If you passed temp test, and you passed air and heated air test for 'a' value change, call it good and put it back. The FSM is ambiguous because you are only looking for trend, not real numbers (unless off OBDII port). Sound like you have them.

A better strategy might be to find an OBDII reader to look at some of the measuring blocks as the truck is running. Lots of autoparts stores have them available for free (if you can take the comments of the guy working it).

The computer should pop a MAF code if it's out of range. For 800rpm idle problems, I'd be cking all the vacuum lines first. Then roll thru your sensor values vs FSM to make sure you are in spec (IAT, ECT, etc.)

HTH

Scott Justusson
QSHIPQ Performance Tuning
Chicago
94 FZJ80 Supercharged

 

[Grench]

Standard OBDII that the parts stores will let you check out only returns the error code. I have one if you want to borrow it, but it sounds like you're already getting the codes out.

I've been thinking about getting one of these for just these types of questions.
http://www.pureenergysystems.com/store/ScanGauge/

Does anyone have one? Does it work as claimed with our '96-'97 TLCs?

 

[Grench]

A better site for that... Version II
http://www.scangauge.com/