MAF Voltage readings

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

After reading some interesting data on a TDI related site, where the voltages of the MAF sensor was measured at different rpms, I checked the MAF on my CRD. It is little more than a device in the top of the air filter box that converts air flow mass to an electrical voltage that is fed to the ECM.

EGR OFF idle (750 rpm) 1.75 VDC
EGR ON idle (750 rpm) 1.25 VDC ( seems correct, egr afc valve closes down, reduces fresh air intake volume while egr gas is ingested)

(assume EGR on while these readings were taken as no WOT was reached)

800 rpm 1.5 VDC
900 rpm 1.6 VDC
1000 rpm 1.7 VDC
1100 rpm 1.8 VDC
1200 rpm 1.9 VDC
1300 rpm 2.0 VDC
1400 rpm 2.1 VDC
1500 rpm 2.2 VDC
1600 rpm 2.3 VDC
1700 rpm 2.4 VDC
1800 rpm 2.5 VDC
1900 rpm 2.6 VDC
2000 rpm 2.7 VDC
2100 rpm 2.8 VDC
2200 rpm 2.9 VDC
2300 rpm 3.0 VDC
2400 rpm 3.1 VDC
2500 rpm 3.2 VDC
2600 rpm 3.3 VDC
2700 rpm 3.4 VDC
2800 rpm 3.42 VDC
2900 rpm 3.45 VDC
3000 rpm 3.5 VDC
.
4000 rpm 3.99 VDC

Based on the VW MAF readings, the readings on the higher rpm seem low - the VW readings ran all the way up to 5 VDC. The VW readings were around 1.7 VDC at idle. Anyone else measure what the MAF is doing voltage wise? These readings were taken wth a DVM, with ground probe to body ground and the positive lead on the blue-green wire on the MAF connector, which is the farthest right on the MAF connector viewing it from the top.

SteveInMD · **Posted:** Sat Sep 09, 2006 7:23 pm

I haven't checked the voltage, but I just replaced the MAF on my 1999 WV Jetta TDI. The car had no power, and now it runs like new.

Joe Romas · **Posted:** Sat Sep 09, 2006 7:24 pm

Ranger1

My son now has my 99.5 tdi but I still have a vag-com setup and am looking foward to see if the F31 recall allows me to probe my crd. Vag-com works fine in "generic obdii" mode on my 99 cherokee and a 96 Cherokee. When hooked to my CRD it can't find any controlers in obdii mode so maybe the recall will help. Do you know if the CRD's are iso9141 standard? Also on the tdi's what rpm do you see 5v on the maf as they redline around 5k :?:

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

It's actually 4.5 volts from 4500 - 5000 rpm a 1.9 Liter TDI engine with a Bosch MAF. That is ~ 450 - 500 Kg/hour mass airflow. The Pierburg is about 4.75 VDC at 4500 rpm. At nearly a full liter larger on the CRD, I'm thinking it should be reading somewhat higher in MAF. The highest I've seen on mine from the OBD was 15Lbs/min or 6.08 Kg/min or 408Kg per hour. That is about what the 1.9Liter TDI engine pulls at 4000 rpm. Seems to me the CRD should pull more than that. No good information on how much from idle to 4300 rpm in the FSM - anyone with the diagnostic manuals for the CRD have this information?

I believe the CRD is iso9141 - but my obd reader uses either the SCI or another bus to pull data, depending on which cable I use. At the very least, by law, you should be able to read emissions data, which includes temp and maf readings.

PS - I don't have a TDI to read the data - pulled the data from someone who did the readings. Used his readings as a baseline to compare the voltage measurements I took on the CRD and my MAF readings to see if there was any correlation. At idle, the CRD is close to the TDI readings, but seems to be weak as rpm climb if I use voltage readings as a guide. Would be nice to know what the expected values are. I think these might be in the diagnostic manuals for the CRD, at least in voltage readings/rpm values.

Joe Romas · **Posted:** Sat Sep 09, 2006 8:40 pm

Is it possible that it's a limitation of the MAF and 4.5 is the max expected flow regardles of the actuall amount of air flow that will vary depending on engine size :?:

Also if the source voltage is 5v then you can't really expect much more :shock:

I'm trying to wait for the LBJ recall before I take mine in and get both recalls and hopefully 18-023-06 in one trip

I really hope vag-com works after the f-31 recall, it gave interesting data on my 99 cherokee.

SteveInMD · **Posted:** Sat Sep 09, 2006 9:11 pm

I don't really understand why the actual voltage matters. As long as the computer is calibrated to respond correctly at any given voltage, the engine should be operating a peak performance. It doesn't matter what the response curve looks like.

AZScout · **Posted:** Sat Sep 09, 2006 10:53 pm

I'm sorry but I don't know what all these numbers represent. Could someone explain please?

Thanks!

Joe Romas · **Posted:** Sun Sep 10, 2006 7:29 am

AZScout wrote:

I'm sorry but I don't know what all these numbers represent. Could someone explain please?

Thanks!

The maf is Mass Air Flow sensor. It meters the airflow and sends a voltage back to the engine management computer. On our CRD's it's somethng to think about once your on your third or forth transmission :lol:

A bad maf severly limits the power of the engine because it does not correctly measure the amount of air at mid to upper rpm ranges. Example, a 99.5 jetta tdi won't go over 3k rpms. It's maf is bad :shock:

greiswig · **Posted:** Sun Sep 10, 2006 12:45 pm

SteveInMD wrote:

I don't really understand why the actual voltage matters. As long as the computer is calibrated to respond correctly at any given voltage, the engine should be operating a peak performance. It doesn't matter what the response curve looks like.

This occurred to me, too. 5V is simply the max supply voltage, usually, and we don't even know that for sure here. Although it does make sense that they'd follow that standard.

However, isn't it the case that these measurements were taken with the vehicle in park, no load on the engine? Is that the same scenario for the VW TDI measurements? I guess I would expect that full voltage (max airflow) wouldn't be reached until the vehicle is under load at WOT. From what I can tell from this thread, for all we know the MAF on the CRD is actually delivering better (i.e. more fine-grained) information to the computer by not "topping out" early.

Thanks for the measurements, Ranger1!

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

The measurements on the TDI were taken with a special harness and an ocilliscope while driving. Those conditions will vary the flow as shift points occur. One of the bad MAF measurements on a TDI showed a poorly performing MAF sensor with low voltages running about 15% low voltage accross the entire range - with no codes set but the owner reporting extremely sluggish performance. With the TDI's, a VAGCOM can read the MAF flow per cylinder stroke and electronically see whether a problem is brewing - an option not available for our CRD's unfortunately.

I did find a bad point on my MAF, between 1100 and 1200 rpm, where the output of the MAF drops to 0 VDC consistently, then jumps back to in range at around 1300 rpm. This corresponds to an rpm dependant hesitation I've noticed since new when the engine is cold - it shudders at that point if the engine is cold and the rpm is run through that range, on both acceleration or deceleration. The question now is the MAF faulty or is a fluttering FCV causing the problem.

Some research shows that MAF sensor performance problems, with low output and bad points of reference voltage along the entire rpm curve are somewhat common. They apparently aren't bad enough to set a code, but can cause drivability problems. Before anyone goes off and starts worrying about their MAF sensor, I wouldn't unless you have a really strong reason to believe that something is wrong with your MAF. Drivability problems can be caused by a lot more than a weak or bad MAF sensor. With a new MAF sensor running about $90.00 the need to be sure its bad before buying a new one is real.

Joe Romas · **Posted:** Sun Sep 10, 2006 5:22 pm

Ranger1 wrote:

The measurements on the TDI were taken with a special harness and an ocilliscope while driving. Those conditions will vary the flow as shift points occur. One of the bad MAF measurements on a TDI showed a poorly performing MAF sensor with low voltages running about 15% low voltage accross the entire range - with no codes set but the owner reporting extremely sluggish performance. With the TDI's, a VAGCOM can read the MAF flow per cylinder stroke and electronically see whether a problem is brewing - an option not available for our CRD's unfortunately.

I did find a bad point on my MAF, between 1100 and 1200 rpm, where the output of the MAF drops to 0 VDC consistently, then jumps back to in range at around 1300 rpm. This corresponds to an rpm dependant hesitation I've noticed since new when the engine is cold - it shudders at that point if the engine is cold and the rpm is run through that range, on both acceleration or deceleration. The question now is the MAF faulty or is a fluttering FCV causing the problem.

Some research shows that MAF sensor performance problems, with low output and bad points of reference voltage along the entire rpm curve are somewhat common. They apparently aren't bad enough to set a code, but can cause drivability problems. Before anyone goes off and starts worrying about their MAF sensor, I wouldn't unless you have a really strong reason to believe that something is wrong with your MAF. Drivability problems can be caused by a lot more than a weak or bad MAF sensor. With a new MAF sensor running about $90.00 the need to be sure its bad before buying a new one is real.

Having had a bad maf on tdi I can tell you a good way to test them is to unplug it and see if it runns better. If it does then the maf is bad. TDI Diesel MAF's were originally lots more then the $90 you mention. Never did get a cell though>
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MAF Voltage readings

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