Hi folks,

Question regarding my 2004 XJR

I don't have a pic yet, but we were cruising around last night and I had the diagnostic tool hooked up. I was watching the MAF sensor data and it was averaging around 20, but would spike up to 80 briefly. Does this sound normal?

Thanks as always!

 

No the spiking does not sound normal to me.
I have an idea that the MAF should be about 4 g/sec
That's probably at idle

 

Was that at constant throttle? MAF can change quickly and drastically with a little foot work!

 

Here is a video of the MAF sensor data as my wife drives around town and the local ring road. Top speed ~55 MPH Sorry for it being rotated and shaky at first. It's not captured on this vid, but as she accelerated onto the ring road from about 25 MPH to 55 MPH the reading s shot up to ~110, then quickly dropped down to ~6.8,, Not sure if this is normal or if the MAF is bad.

 

I don't know what the numbers should be, but when you mash the go pedal, the engine takes in more air, so that's not exactly alarming. If you're not getting mixture codes (like system too lean) and a check engine light, then worry less and drive more. It sounds like you saw data you didn't expect, but have no idea what that data should be, and actually had no real reason other than curiosity to be even looking at that data. If you're not troubleshooting something, then leave it be. If you ARE troubleshooting something, maybe lead with that.

 

Hi Ethan,

Whenever we are interpreting MAFS signals, it is important to know what units the scan tool is measuring. Your tool is measuring in grams-per-second (g/s). Other common units include kilograms-per-hour, pounds-per-hour, pounds-per-second, etc.

As meirion1 mentioned, a common rule of thumb is that at idle, the MAFS signal in g/s is typically about equal to, or a little higher than, the displacement of the engine in liters. So for a 4.2L engine we would expect the MAFS signal at idle to be in the range of 4-6 g/s. As the accelerator pedal is depressed and the engine inhales more and more air mass per time, the reading can climb to 20, 40, 60 g/s or more. When we are diagnosing MAFS issues, a common practice it to take readings at idle, 1,500 rpm and 2,500 rpm.

I second wfooshee's advice to just enjoy the car unless you have any misbehaviors or diagnostic trouble codes stored or your fuel trims exceed +/- 10%.

Cheers,

Don

 

We did have an issue with a left turn stall. We looked for causes, things like wheel speed sensor, ignition, and also the maf sensor. We resolved it with an ignition issue. However in looking at the maf sensor and looking what they are supposed to be it was unclear if it was performing correctly. I don't know what the waveform should look like, hence asking here.

 

Thanks Don, I will look at those engine levels. I think it may be fine.