MAF Sensor voltages

[Legacy777]

I had a passenger in the car today, and wanted to see what sort of readings I was getting on the select monitor, specifically the MAF sensor.

The three highest voltage readings I got were at full stock boost and around 6000 rpm.

5.6 V
5.1 V
4.8 V

What gives? I thought the stock MAF maxed out at 5 V?

The injectors did seem to be pegged or open quite a bit....I think they were somewhere around 20 ms or something.

I ddin't get any bucking......it didn't seem to pull extremely hard.

During a full throttle pull, full boost run, the O2 sensor reading was 0.7 - 0.8. So she's definitely staying rich.

I also checked the load reading.....It read like 225 or something one time

Thoughts....comments?

[sammydafish]

where are you referencing ground from? Make sure it's ground from the ECU, and if there is that much of a difference between grounds, you'll probably benefit from the grounding mod.

[vrg3]

Uh, 5.6? Putting aside the question of whether or not the ECU can read a voltage that high from the sensor, it's impossible for the ECU to report a QA of 5.6V to the Select Monitor. It sends an 8-bit value and each bit is one fiftieth of a volt, so the highest it can go is 255/50=5.10V.

Are you sure you didn't misread the display? If you didn't, then the Monitor must have been doing something funky...

The sample rate of the Select Monitor is pretty low, and the ECU doesn't always keep it updated when things get hectic, so you can't really rely too much on it for information on transient or very high-load conditions.

[Legacy777]

My passenger was doing the reading, so either they misread things or the select monitor was going screwy.

Does your scan tool program have a more reliable sample rate?

I'm more curious about where other people's readings are utilizing similar measuring equipment, ie your scan tool. Is that a reliable measuring device?

[vrg3]

My scantool has a higher display rate than the Select Monitor, but it doesn't really help much when the ECU stops reporting at high loads and RPMs. The numbers reported by my scantool should be the same as those reported by the Select Monitor.

[Legacy777]

I guess I'm curious though.....you say the ECU stops reporting at high loads and rpms.

I've read numbers at high rpm and loads from the select monitor, and they appear to be accurate. Are these numbers just made up / inaccurate?

I'm not doubting what you're saying, just trying to understand what I'm physically seeing.

[vrg3]

In my experience, they are just reported less regularly... you might only get one sample every second or two, for example. Occasionally it'll take so long that the Select Monitor displays an "ERROR 2" message for a split second. When a number does appear, it is correct, though.

But maybe this is only when exceeding the OEM range of loads and such...

[Legacy777]

Yeah, I've got those error 2 numbers occasionally on things like the IAC valve or wastegate....and that's when just sitting at idle.

I need to do some more tests. I may have a friend drive my car, and I'll look at things.

Other option, which may be more productive/better is logging data from the perfect power. I just need to confirm whether or not I should hook up the temp, amp, & O2 inputs. If I get an answer, I may try and solder the perfect power up to your harness tonight.