T5 MAF sensor voltage range and clicking from ignition coil.

NewKidOnTheBlock · Post by **NewKidOnTheBlock** » Thu May 07, 2020 3:34 am

Hi All,

I'm still working to investigate a sound which I suspect to be pre-detonation at full boost+high revs and I've been looking in detail at my MAF. This failed a couple of years ago and was replaced with a pattern part. I have back probed the socket over pins 1 and 4 and am getting a range from ~1.3v at idle to ~5.7v at WOT and high RPM.

I've been looking for more information and the closest I've found is that from some forum posts I believe the ECU only reads up to 5v and I found this video where they are reading 1.7v at idle, albeit over pins 2 and 4 rather than 1 and 4 (1 and 2 are both grounds, when probing the MAF I found continuity between pin 2, a ground and pin 3 the 12v feed, so I believed that pin 2 is the ground for the 12v feed wire).

My car is a 1998 V70R, does anyone else know the ideal voltage figures for this?

Also... while I was probing this I noticed I could hear a very faint clicking in that area, after moving my ear around I found that it's coming from the ignition coil. Now this isn't the 'snapping' click usual to a HT leak, but a very feint click only heard when I really put my ear right next to the coil. Can anyone else confirm if theirs does this?

Before people start commenting "just replace them, OEM is best yadda yadda", I know that's an approach I could take but I am trying to learn and improve my understanding rather than just throw money at parts and randomly guess at the fault. I have ordered myself an OBDII scanner which I'm hoping will be able to give me the actual ECU g/s reading from the MAF which I hope will show if the MAF is maxing out which would throw my fueling out and possibly cause pinking.

Thanks

Post by **abscate** » Thu May 07, 2020 4:11 am

1.7 volts at idle is listed in Alldata, going up linearly with air flow of course

I don’t know what the supply rail voltage is, so it could cap at either 5 or 12 volts, or even something in between

MAF failures are proportional to how much you fool with them, by the way.

Get the pin outs from the Bosch documentation. Look for the Bosch part number and google that. Continuity tests on digital circuitry can hurt stuff so be careful doing that

My ME7 MAF pulls supply voltages from both the injector amd the sensor ring but your earlier At is probably different. Wiring diagrams showing this are on the web and also linked in threads here, by agreement with Volvo.

NewKidOnTheBlock · Post by **NewKidOnTheBlock** » Thu May 07, 2020 4:16 am

Thank you. Supply voltage to the heating element is 12v. The voltage over the signal loop on mine seemed to cap at 5.7 for approximately the last 1000 rpm in the range.

NewKidOnTheBlock · Post by **NewKidOnTheBlock** » Sat May 09, 2020 5:32 am

So I got my OBDII scan tool today and read the MAF readings while the car was running, idle I'm at around 4-4.7g/s, full throttle at redline I'm getting a max reading of just over 200g/s. Does anyone have any figures to compare?

The other thing I noticed when scanning was that the throttle position sensor reads as 11% when not touching the pedal, is this normal? I expected it to be 0 but possibly not? I found that when with the pedal flat on the floor I only get a reading of 84.7% - this seems even stranger - again does anyone have any figures from their cars? If my car's thinking I'm only at 3/4 throttle when infact I'm at full throttle would this also force a lean state?

Thanks

NewKidOnTheBlock · Post by **NewKidOnTheBlock** » Sat May 09, 2020 6:26 am

... So I found this youtube video where the guy's checking the voltage and he's getting 0.59v-4.5v over the TPS

Doing the same test I get 0.55v-4.09v.

This seems to corroborate with my scanner as I'm at around 90% of the voltage I'm expecting.