Hi
I'm moving this from inside another thread so apologies if you've read it twice. I'm trying to find out if my MAF sensor is faulty and was advised to post my peak values at 100% throttle:
My peak value wasn't at 100%, it was 216.7 at 62% throttle
At 100% throttle I have 9 values (couldn't keep it at 100% for long! (story of my life!)):

190.96
176.08
169.31
167.79
160.9
156.19
154.74
148.58
108.52

At low throttle my values are around 4.8-5
Note that these are not in time sequence, I hit the throttle a couple of times and these are just the ones at 100% throttle sorted max->min
Can anyone let me know if these look about right, or do I need values at 2500ish rpm too? I've seen the article in jagrepairs but the values are for an NA engine.

Many thanks!

 

Long time ago that I measured that, but you should be roughly getting about 320 gr/sec.

To get a more detailed measurement, select only the MAF value for recording, put your gear lever in 2nd (3rd is better, but may be too fast for the local law), and drive until you hit the rev limiter.

 

I have got 388-390g/s. Temperature was +8C. BMC cone filter.

 

Hi the peak value should be at about 6krpm, and sub 200 looks wrong for an XKR my XK8 4.2 shows up as 195g/s and I thought that was low.


But it would be good to see some real measured values from some others.

 

Thanks all definitely didn't get to 6k so I'll try a run like Avos suggested

 

Doing WOT runs in the XK is tricky to get a clean run, as you cant hold it in any gear except 1st and in 1st you will spin the wheels.


1st is not ideal either as you will get a limited number of data points for a nice graph but you have no choice really.


Put it into sport mode so it will start in 1st then ease it into WOT over half a second to avoid wheel spin. If you record the data you will get something like this (these ones are plotted against time rather then RPM as you get twice the data points).


You can see 4 attempts here, 3 with wheel spin and one where I eased it in. My peak is about 195 but so far no one else has posted up any other 4.2 NA results so I also have no clue if mine is faulty or not.

 

Thankyou all for the tips. Here's my run in 2nd up to the limiter - my peak is 269. This seems a little low from some of the posts above. I have previously tried cleaning it with electrical contact cleaner; is MAF cleaner much different? Would you replace with these values?

 

For the time being you need to put to one side the "what it should be" comments until there is some more evidence.


In a previous post ccfulton said that he had measured the MAF on a bench to calibrate it and found that the ecu was reporting values less that the calibrated air flow. The ecu reads a voltage from the MAF and acts on that value, then probably calculates a g/s value to feed out of the OBD2 port.


My car peaks at 195g/s which also seems low, so ccfulton's suggestion seems to fit my car too.


Thus what is needed is a real comparison to other real cars.


However, last night I cleaned my MAF (with break cleaner) and the peak value dropped by 5g/s, yes I know I should have used MAF cleaner so don't give me a hard time.


As a result I bought a new one from ebay last night as they are fairly cheap, I will get it in another couple of days and will let you know if it also reads 195g/s


Air Flow Mass Meter Sensor for SUBARU MAZDA JAGUAR XK XJ MAF 22680-AA310 | eBay


Here is some flawed thinking that others can comment on;


if we say that my 195g/s ---> 290bhp (was 300 when new so lets say I've lost 10)
your 260g/s ----> 260/195*300 = 386bhp, looks like you have gained some, must be the car wax you use or you lose some hp to drive the supercharger.

 

mafv g/s lb/min hp
2.00 16.81 2.22 22
2.05 18.33 2.42 24
2.10 19.93 2.64 26
2.15 21.62 2.86 29
2.20 23.41 3.10 31
2.25 25.30 3.35 33
2.30 27.29 3.61 36
2.35 29.38 3.89 39
2.40 31.58 4.18 42
2.45 33.89 4.48 45
2.50 36.31 4.80 48
2.55 38.85 5.14 51
2.60 41.50 5.49 55
2.65 44.28 5.86 59
2.70 47.17 6.24 62
2.75 50.19 6.64 66
2.80 53.34 7.06 71
2.85 56.62 7.49 75
2.90 60.04 7.94 79
2.95 63.59 8.41 84
3.00 67.27 8.90 89
3.05 71.10 9.41 94
3.10 75.08 9.93 99
3.15 79.20 10.48 105
3.20 83.47 11.04 110
3.25 87.90 11.63 116
3.30 92.47 12.23 122
3.35 97.21 12.86 129
3.40 102.11 13.51 135
3.45 107.17 14.18 142
3.50 112.39 14.87 149
3.55 117.79 15.58 156
3.60 123.35 16.32 163
3.65 129.09 17.08 171
3.70 135.01 17.86 179
3.75 141.10 18.67 187
3.80 147.38 19.50 195
3.85 153.84 20.35 204
3.90 160.49 21.23 212
3.95 167.33 22.14 221
4.00 174.36 23.07 231
4.05 181.58 24.02 240
4.10 189.01 25.01 250
4.15 196.63 26.01 260
4.20 204.46 27.05 271
4.25 212.50 28.11 281
4.30 220.74 29.20 292
4.35 229.20 30.32 303
4.40 237.87 31.47 315
4.45 246.76 32.65 326
4.50 255.86 33.85 339
4.55 265.19 35.09 351
4.60 274.75 36.35 363
4.65 284.53 37.64 376
4.70 294.54 38.97 390
4.75 304.79 40.32 403
4.80 315.27 41.71 417
4.85 325.99 43.13 431
4.90 336.95 44.58 446

 

wow that's quite a bit higher than mine! Think I'll get a new one to be sure, since I've already tried cleaning. Thanks for the data, I'll post back when I have results. RaceDiagnostics - good luck with yours!

 

Forget the true airflow, the gr/sec is just a calculation from the voltage, and you can only compare this with similar cars, so AJ27 SC engines (not AJ26 like I guess XJR-99 is showing?).

I do think 269 is on the low side, about 300 would still be ok, but it's way to long for me to remember all the details of my measurements although I am relatively sure it was a stock setup for the 320.

PS Personally I don't like the cleaning part, and it would not surprise me that it affects the MAF sensors sensitivity, so would limit cleaning actions only if there is really an issue/heavy dirt.

 

I dropped in the new MAF today, peak reading went from 195g/s to 239g/s.


Clearly the old one is duff, this figure also conforms to the 0.8 rule.


239.18/0.8 ~~~> 299 bhp.


Looks like you should shell out for a new one.

 

Deleted and moved to new post.

 

Deleted and moved to new post.

 

Thanks for the update. Mine arrived today, fingers crossed it's not a dodgy one like yours turned out to be! (it was about the same price though...)

 

Put my new MAF in today at lunch - runs fine but the trims haven't changed much at all it seems, but I didn't do a hard reset.

My peak airflow is up to 365 g/s!