Thread: MAF Voltages (VQ Table)

Hey John, I found these two VQ tables claiming to be Cobra maf's. Do they look about right?

MAF 1 - Maf 2
757 170
885 212
976 266
1122 334
1277 416
1441 512
1587 623
1761 750
1957 893
2174 1051
2402 1226
2673 1417
2959 1625
3263 1851
3583 2093
3922 2354
4278 2633
4652 2929
5043 3243
5456 3576
5886 3927
6341 4298
6817 4688
7313 5098
7836 5527
8384 5979
8852 6450
9399 6949
9947 7470
10677 8014
11316 8587
12000 9188
12700 9820
13400 10485
14300 11185
15000 11925
15800 12706
16600 13533
17500 14410
18300 15341
19400 16311
20300 17344
21500 18448
22800 19622
24300 20875
25600 22214
27300 23648
28800 25184
30390 26834
32000 28300
33600 29800
35400 31400
37000 33100
38500 34600
40400 36200
42200 37900
43800 39600
45500 41200
47400 42800
49152 44700
50790 46300
52428 48200
54067 50000
55900 51900

I can share some of my experiences playing with different MAFs(Nissan and Ford’s).

Changing the K value alone would be not sufficient when using a bored MAF housing or placing the MAF sensor in a bigger housing like a 3.5” pipe. It would be very inaccurate. It would be like trying to solve the fueling demand by upping or lowering the fuel pressure. Some part of the fuel map would be ok but the rest would be way off. In order to be perfect and to make sense of value in your fuel table, you would also have to modify the VQ table. Basically, build your own VQ table and that what I did for some of the Ford 80mm and 90 mm MAF.

Think of the K value as injector multiplier instead of a MAF scaling number. The K value would change the fueling globally.

You can run any MAF you want as long as MAF sensor matches the housing and VQ table. If everything matches up, all you need to do is change the K value. But if you have an unknown MAF sensor or place the sensor in a different housing, then you have to build your own VQ table.

Mind sharing how you built your own VQ table?

I understand what you are saying and that is why I said that after applying a simple percentage difference to get it in the ballpark, you should then compare STFT (Short Term Fuel Trims) vs MAF voltage to modify the VQ table directly.

I did not intend for it to read that touching the VQ table was not necessary at all.

I do not like to think of the K value as an injector constant as it affects a lot more than just injector scaling. The K value is more of a global maf scaling constant than anything.

I wish i was as smart as my younger brother.

Shush..

I completely forgot I had your stock DE maf at the shop.. maybe I can work with that to try to get a bored DE maf curve done.

A wideband and a lot of number crunching, lol. I'll get into the detail a little later.

+1... Yeah id really apreciate it aswell. Id like to know a systemitic way of actually revising the vq maps for larger housings. Thanks!

I went about it a different way, logging the wideband and airflow meter voltage output and comparing their values against the fuel map. I like to think of the fuel map as the commanded air fuel ratio map, it helps to make better sense of the value # and what they rerepresent.

The formula for the afr in the fuel map is 128/(128 + cell value) X 14.7 in open loop with no 02 feedback.

So, for idle or cruising, if I want 14.7 afr, the cell value would be 0 which is 128/(128 + 0) x 14.7 = 14.7 afr.

For WOT part of the fuel map,if I want 13 afr, it would be 16 or 128/128 + 16 X 14.7 = 13.06 afr.


Now if the wideband afr does not match up with the commanded afr map, then the K value and Vq table need to be address.

The above example is for the B13 based ecu fuel map.

I have a system now where I can make a pretty accurate guess as to what the afr curve will look like for a set K value with different VQ tables.

For example, just by doing some simple calculation, I can tell you that the VQ table for Calum E60 is not the original. Looks like somebody modified it. At 4 volts and above the Calum E60 will give you a leaner afr. It’s not a smooth curve.

I use your above mentioned method when dialing in vq tables on other maf based cars (evos, subarus, etc).

In Rom Raider there is a whole section devoting to tuning the MAF compensation table. Since they have a wideband from factory, it uses the STFT up to about 2.5 volts and a TON of data points of STFT vs MAF Voltage to come up with a adjustment curve. It works ok, but generally is easier to do it by hand.

I was never 100% convinced that the obd1 fuel table is setup in this style of format, but in this case it would work ok to assume it was.

Thanks for sharing the info as it will help people further dial in custom vq tables.