MAF readings

azureblue · Post by **azureblue** » 22 Apr 2018, 20:11

I have been trying to find why my 2001 V70 T5's gas mileage is slowly dropping. Nope, not the air filter or plugs, or gas, and no codes so I took a guess at the MAF. The sensor looks fine, and was clean. I believe the PO replaced it, because the torx screws are not the originals - just plain old torx screws. So I had a friend use a small reader and he got: MAF (LB/M) = 0.36 at 670 RPM, and 1.1.2 at 2100 RPM. This looks Ok to me, but I would like to check to make sure..

Thanks in advance..

One other question - on the reader there : ST FTRM1 (%) = -1.6 at 670 RPM.. What is that an abbreviation for?

Post by **abscate** » 23 Apr 2018, 04:34

Short term fuel trim ...the amount that the ECU has to adjust the fuel injection to make stoichiometric air to fuel ratio.

A classic vacuum leak from a split hose results in more air in the engine after the MAF, so the reported air level is lower than actual, the OXS sensor then reports a lean condition of too much oxygen, so the ECU adjusts the short term fuel trim by raising the injection length by some percentage of its default range, set by rpm.

WITIK - what I think I know

I believe the percentage refers to the the fraction of pulse length.,,one of the real gurus here will confirm.

Post by **oragex** » 23 Apr 2018, 06:52

These were my readings on my otherwise good MAF

azureblue · Post by **azureblue** » 23 Apr 2018, 08:38

Thanks for the vid, but I'm not sure if the readings are comparable, since mine came via the OBD2 port, and the numbers look like they are in different types of measurement. For sure, I never got anything above 200........

PS the 2K RPM reading was 1.12. Ignore the extra decimal point...

Post by **mrbrian200** » 23 Apr 2018, 10:07

As a general rule it's the long term fuel trim you want to initially be looking at. Short term will vary under conditions. If long term is +/- by more than couple percent then you've got something to follow. If your scanner shows Short Term, it should also display the long term parameter likely labeled LT FTRM*, what does it say?

Note * is a wildcard character, may or may not be "1"

azureblue · Post by **azureblue** » 23 Apr 2018, 17:56

Thanks---- LT is 3.9.. is that good?

Post by **mrbrian200** » 23 Apr 2018, 20:07

+3.9 LT is just enough to look at. The ECU is metering more fuel to compensate for a lean condition (too much air), or what it perceives is a lean condition.
1st three things I would check would be 1. check for leaks in the intake system. On turbo vehicles there's enough air piping criss crossing around that the only way to be really certain about this is to have a smoke test performed. 2. have a tech run a test to check the response time of the oxygen sensor. If it's been more than 90,000 miles since this has been changed the chances of a problem becomes more. Generally they will read (falsely) a little lean for some time before its bad enough to cause a check engine light and/or irritating driveability issues. 3. dirty/plugged fuel injectors can cause a lean condition, as also can a plugged fuel filter. Typical remedies for plugged/dirty injectors vary by opinion and budget. Generally the more you spend the more likely you'll see success, but spending more money by no means is a guarantee of success.

QUARKS40 · Post by **QUARKS40** » 24 Apr 2018, 05:45

mrbrian200 wrote: ↑23 Apr 2018, 20:07 Generally the more you spend the more likely you'll see success, but spending more money by no means is a guarantee of success.

+1