Low actual air mass readings

I recently replaced the MAF with a new Bosch MAF. The power is restored. But the actual air mass readings at engine rpm > 3000 are still low. I have tested with VCDS-Lite. In measuring group 003, at engine rpm > 3000, the actual air mass is staying in the 700-750 range and barely touches 800. I've compared the requested vs. actual air mass in a graph. The actual stays below the requested most of the time.

Here's what I've checked/done:
- Checked/cleaned the snow screen

- Checked the intake, is not clogged
- Fixed an exhaust leak
- Replaced a couple of vacuum lines with good quality silicone hose, rest of the hoses look ok
- Tried testing group 003 with two different used (but known good) MAF's
- New air filter with pre-filter
- When accelerating, I can hear the turbo spin, so it seems to be working

Still I got almost same results for actual air mass values. Fuel economy is staying in the 5.7-5.9L/100kms. range. I expected it to be below 5.5L/100 kms. with the new MAF.

What can I check/do further to troubleshoot this?

Thanks.

Do you have a boost leak?

imo000 said:

Do you have a boost leak?

Click to expand...

No idea about that

I did map group 011 in measuring blocks. In the graph that I did, the actual boost readings are higher than the requested at >3000 rpm, so I think it's ok, however am not sure. How can I check for boost leaks? Thanks.

amit9 said:

No idea about that

I did map group 011 in measuring blocks. In the graph that I did, the actual boost readings are higher than the requested at >3000 rpm, so I think it's ok, however am not sure. How can I check for boost leaks? Thanks.

Click to expand...

A smoke machine or just a cheap lit cigar will do.

check the snow screen in the duct going from the air filter to behind the headlight? its a very fine mesh that where Im from clogs instantly. I cut mine out.

Updatelee said:

check the snow screen in the duct going from the air filter to behind the headlight? its a very fine mesh that where Im from clogs instantly. I cut mine out.

Click to expand...

Thanks, yes already did, updated my first post.

amit9 said:

In measuring group 003, at engine rpm > 3000, the actual air mass is staying in the 700-750 range and barely touches 800. I've compared the requested vs. actual air mass in a graph. The actual stays below the requested most of the time.

Click to expand...

This could perfectly normal, depending on driving conditions. Are you experiencing performance issues you believe are MAF related?

You should log group 003 during a wide open throttle run from 2000rpm to 4000rpm in 4th gear. Only under these circumstances is MAF (actual) expected to consistently reach the MAF (specified) value.

Simon

P2B said:

This could perfectly normal, depending on driving conditions. Are you experiencing performance issues you believe are MAF related?

You should log group 003 during a wide open throttle run from 2000rpm to 4000rpm in 4th gear. Only under these circumstances is MAF (actual) expected to consistently reach the MAF (specified) value.

Simon

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Well, the fuel economy numbers are not what I expect after putting in a brand new bosch maf.

Referring to this: https://www.ross-tech.com/vag-com/cars/tdi.html

Air system part I: MAF

• Go into Engine measuring block 003
• Start Logging data
• In a high gear (4th/5th), give full throttle from 2500 rpm up to 3500rpm.
• Find and Open the Log file in Windows Explorer
• Graph MAF actual -vs- rpm in Excel
• The MAF is OK if the actual value is at least 850-900 mg/h at 3000 rpm.

My test was done in 2nd/3rd gear and logging group 003 past 3000 rpm. Just wondering, how is 3000 rpm in 2nd/3rd gear different than 3000 rpm in a higher 4th/5th gear? Is the MAF supposed to give different actual readings in higher gears?

Thanks.

Did you check and make sure your egr valve is not stuck open slightly? engine sucking exhaust gases will pull less through the maf. Higher gears means more load which requires more boost and sucks more through the maf.

amit9 said:

• In a high gear (4th/5th), give full throttle from 2500 rpm up to 3500rpm.

Click to expand...

I highlighted the most important instruction. Did you collect logs at WOT?

Simon

derek5120 said:

Did you check and make sure your egr valve is not stuck open slightly? engine sucking exhaust gases will pull less through the maf. Higher gears means more load which requires more boost and sucks more through the maf.

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I did notice that the wires going into the ASV solenoid (N239) connector are not in the best shape and are worn out. It looks like it's a common problem in our ALH. Can that cause the egr valve to stay open if it's a bad connection? I will unplug the connector and check the voltage on the pins tomorrow.
Thanks.

P2B said:

I highlighted the most important instruction. Did you collect logs at WOT?

Simon

Click to expand...

Noted Simon, will repair the solenoid connector wires if required, and then do the group 003 and 011 tests at full throttle. I'll post the graphs of the logs.
Thanks.

Here are the results of my testing.

Warmed up at idle:


At idle after 2 minutes:


Group 003 log in 4th gear and went from 2300rpm to 4000rpm (air mass specifed - green line, actual - red line):


Group 011 log in 4th gear and went from 2300rpm to 4000rpm (boost specified - green line, actual - red line):

Are you sure you have the right MAF?

That graph looks a lot like mine did when I installed a MAF from a box of spare parts someone gave me. Turned out to be a PD MAF.

Simon

P2B said:

Are you sure you have the right MAF?

That graph looks a lot like mine did when I installed a MAF from a box of spare parts someone gave me. Turned out to be a PD MAF.

Simon

Click to expand...

Yes Simon, at least the part number printed on the box and the maf indicate that it's for the ALH.

This is what I bought from World Impex in the US:
https://worldimpex.com/volkswagen/jetta/2003/ulik8hho-wtw1/fwd/?result=5128

This is what I received:


Yellow box is a loaner from a local member, it's the Canadian version from Auto Camping. Blue box is what I got, looks like it's the newer US version. Part numbers and barcodes are identical on both boxes.

This is the actual part compared to the Canadian version:


Mine has the part number printed on it with the manufacture date. The loaner part has the part number embossed on it.

Is my N75 failing/bad?

So read up more on the forums about similar issues, and continued my troubleshooting this morning. This time I focused on my N75 valve and turbo actuator. I don't have a full vcds-lite version to do any output tests for the N75 to cycle it repeatedly to check the actuator arm. Hence I did the following tests to verify these two parts.

1. Told my wife to start the car, had an inspection mirror and flashlight focused on the turbo actuator arm. Surprise surprise, no movement of the arm on startup or after shut down. Did a start/shut-down 3-4 times, still no arm movement. The vacuum hose is plugged in to the actuator and appears to be in good shape, not loose. I followed that hose all the way from the N75 to the actuator and it looks good.
2. Unplugged the hose on the vac/top port of the N75. Plugged in a vacuum pump in the hose. With the car started, I got 27 Hg on the gauge, which is good as per this thread - http://forums.tdiclub.com/showthread.php?t=179589.
3. Plugged the hose back in the vac/top port, plugged in the vac pump in the 'out' port, started car, got 17 Hg on the gauge. It dropped to 0 right after car was shut down.
4. Resistance across the N75 connector pins is 17 ohms.
5. Unplugged the connector to the N75, with car started, the voltage across the connector slots is 10.45V? Is that what it's supposed to be? I checked the connector wires and they're ok.
6. Referring to this thread - http://forums.tdiclub.com/showthread.php?t=419530&highlight=n75, I plugged in the vac pump to the vac/top port, covered the other two ports with my fingers, and pumped. I could only get it to 7 Hg on the gauge, and then it would drop to 0 within 5-7 seconds. According to this thread, it points to a bad N75.
7. I have small oil residue on the valve cover under the CCV breather hose clamp. I was trying to clean that area, and I did notice that there's a minor tear at the neck of the breather tube/hose where it bends and goes into the air intake hose. With the car started, I put some soapy water with my hand on the tear, and I didn't see any bubbles. Regardless, I will still be replacing this tube/hose shortly.

With these tests and results, I'm leaning towards that my N75 is failing/bad, thereby not providing enough vacuum to the actuator, hence no arm movement, so turbo is not being activated while driving, hence less air being pulled in, causing low actual maf readings.

Is my troubleshooting conclusion correct?

Thanks.

Your N75 is working perfectly according to the group 11 log you posted above, but I suppose it could have failed since.

The easiest way to test basic function of the boost control system is to go to group 11 basic settings with the engine idling. The ECU wiil cycle the actuator up and down every few seconds.

Simon

Yes I noticed that too in my group 011 graphs, and they have been consistent every time I tested.

My vcds lite version has the "output tests" and "basic settings" buttons disabled, so I don't have access to those options to do the tests the easy way...

Have you put a wrench on the actuator to see if it's moving? Or tried a vacuum pump/gauge on the actuator hose?

2ManyKMfor1Tank said:

Have you put a wrench on the actuator to see if it's moving? Or tried a vacuum pump/gauge on the actuator hose?

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That is going to be my next step. I'm just trying to figure out what would be the best way to get access to the actuator since it's all the way down and hidden behind the block. I think taking out the passenger side wheel should give me access to it. From the top it looks like out of reach and won't get a good view of it.

amit9 said:

That is going to be my next step. I'm just trying to figure out what would be the best way to get access to the actuator since it's all the way down and hidden behind the block. I think taking out the passenger side wheel should give me access to it. From the top it looks like out of reach and won't get a good view of it.

Click to expand...

The best way to get to it is jacking it up and going underneath.

If you have a stubby 14 mm wrench, you can easily get it on the actuator arm from above. Take a mirror if you have to to see where to put it, once you get it, it becomes easier to find it again.