Why is actual air mass decreasing at full load at high rpms?

runningallday

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Jul 22, 2017
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Iowa City, IA
TDI
1999.5 Jetta TDI manual
Thanks for all the tips!! I'll probably start with the safest options and work up! :) can't wait to have my ALH breathing properly again. :D
 

runningallday

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Jul 22, 2017
Location
Iowa City, IA
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1999.5 Jetta TDI manual
What should an intake manifold remove/clean/replace cost at a good shop? Mine has about 180K on it.
You can buy a clean used one on eBay for $60, keep that in mind... Honestly no reason not to just buy a new one and clean it later, then you can put your car back together right away
 

Gothmolly

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Providence, RI
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2002 Golf
You can buy a clean used one on eBay for $60, keep that in mind... Honestly no reason not to just buy a new one and clean it later, then you can put your car back together right away
I'm looking to have it done, any time I work on a rusty car I shear a bolt and end up drilling it out - no WAY I'm trying that on the back of an engine block where I can't even see what I'm doing. Great idea though!
 

runningallday

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Iowa City, IA
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1999.5 Jetta TDI manual
I'm looking to have it done, any time I work on a rusty car I shear a bolt and end up drilling it out - no WAY I'm trying that on the back of an engine block where I can't even see what I'm doing. Great idea though!
You could ask thomas exovcds on youtube, he's done it a lot and seems to be active on there.

The one thing they often mention is heating up the nuts, because you can easily mess up the studs. Not totally sure what nuts exactly they're referring to, because I haven't done the job yet, but you can bet I'm going to follow that advice!!
 

Nero Morg

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2003 Jetta wagon, 2001 Jetta TDI, 2014 Passat TDI
Intake is held on with Allen caps crews, turbo is held on with nuts. You do not need to remove the turbo to take the intake off.
 

runningallday

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Iowa City, IA
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1999.5 Jetta TDI manual
Not as bad as I thought. Scraped out what I could, then left it soaking in some red diesel overnight.


If I work quickly, tomorrow I'll know whether this was the issue.

One quick question, are there supposed to be gaskets between all connections for the egr cooler? Seems like one was missing.
 

Nero Morg

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So all connections have a stamped metal gasket, except the pipe going to the valve itself, if has a composite gasket, that tends to get stuck on the valve.
 

runningallday

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Jul 22, 2017
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Iowa City, IA
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1999.5 Jetta TDI manual
So all connections have a stamped metal gasket, except the pipe going to the valve itself, if has a composite gasket, that tends to get stuck on the valve.
Sweet thanks! Got worried because the egr one didn't have a metal gasket. I have the kit though so they'll be getting replaced.
 

runningallday

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Iowa City, IA
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1999.5 Jetta TDI manual
Ok new update. Took it all apart. It had been ~100k miles since last cleaning, and the manifold only had low to moderate blockage.

I noticed the EGR cooler was difficult to blow through. So I tried to clean it out with 3/16" drill bits (didn't have any longer than 4 inches though), oven cleaner, etc, but didn't really make any progress. So I briefly tried to burn it out with a heat gun. It definitely started on fire for a bit before I gave up.

Put it all back together. Now I notice that there's a "charred-looking film" in my coolant. Maybe it wasn't such a good idea to try to burn out the EGR cooler. Almost wish I would've just deleted it, because it's clear full of soot anyway. :( Might order a race pipe.

But on to the results: On a new high rpm, WOT, it can only maintain actual spec at 850 mg/str until 4242 rpm. After that, it goes down, and was only 715 mg/str at 4578 rpm (at which point I shifted).

Previously, it was at 655 mg/str at 4578 rpm. So by cleaning out the intake, I gained ~60mg/str at 4578 rpm! :D now how do I get the remaining ~135 mg/str, so that I can match actual to spec??? I guess the next step is checking the exhaust?
 
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runningallday

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Jul 22, 2017
Location
Iowa City, IA
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1999.5 Jetta TDI manual
Another thing to note: I have a couple data points while at high rpm with my foot off the gas. It looks like the specified air mass remains at 850 mg/str, while the actual air goes down to ~500 mg/str. Is this because the turbo shuts off?
 

Nero Morg

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2003 Jetta wagon, 2001 Jetta TDI, 2014 Passat TDI
At WOT in 3rd, the maf specified will read 850, but it should still read way above that. There's something else going on. Have you checked for exhaust restriction? How about vnt nozzle movement? Turbo not spooling can cause low maf readings.
 

runningallday

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Iowa City, IA
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1999.5 Jetta TDI manual


Here's the latest graph. Cleaning the intake manifold definitely helped, no doubt about that. But still, >4300 rpm, it's not getting the air it's asking for. I recently installed a boost gauge, connected to the EGR valve, I'm getting plenty of boost.

Also my mileage isn't as good as it used to be. Always used to be >50 mpg. The last trip, I got 44 mpg on the highway, going easy on it. Also my speedometer reads high by 3-4 mph or so, so that number is probably even worse.

I just did some reading, sounds like if I use a temperature gun, I can check the temperature before and after the catalytic converter. If the number is >150 degrees, then it might be restricting flow. After doing some more reading, I think I would prefer having a functional catalytic converter, for lower noise/smell... But ofc I will do the easy temperature test first
 

oilhammer

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Dec 11, 2001
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outside St Louis (where it's safe)
TDI
There are just too many to list....
I have never encountered a clogged up catalyst on any ALH, ever, and this is with many of them modded and well over 300k+ miles. You won't be able to do the temp trick, as the TDI's exhaust cools down too quickly. Unless you can get under the car while it is being run on a dyno under load, you won't get any meaningful data there.

It also sounds like you may have ruined your EGR cooler. Plenty of good used ones out there. If your EGR valve is leaking, or sticking on slightly, the MAF value under full load (when the ECU requests the EGR be CLOSED) could cause some abnormal readings.
 

runningallday

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Jul 22, 2017
Location
Iowa City, IA
TDI
1999.5 Jetta TDI manual
I have never encountered a clogged up catalyst on any ALH, ever, and this is with many of them modded and well over 300k+ miles. You won't be able to do the temp trick, as the TDI's exhaust cools down too quickly. Unless you can get under the car while it is being run on a dyno under load, you won't get any meaningful data there.

It also sounds like you may have ruined your EGR cooler. Plenty of good used ones out there. If your EGR valve is leaking, or sticking on slightly, the MAF value under full load (when the ECU requests the EGR be CLOSED) could cause some abnormal readings.
The EGR cooler still is mostly full of soot, I could blow through it but not very well, it seems impossible to clean properly without destroying it. I did read you can bake it at 500 degrees until it's clear, that may be valid, but I didn't have time to figure that out and needed my car back.

Everyone talks about how we should keep EGR because it helps warm up the coolant. But I'm not sure if that's a valid argument anymore, because at 180k miles, my EGR cooler was pretty much completely plugged. And I wonder how much this EGR "restriction" prevents EGR from working at all. What if all this talk about "low sulfur diesel" etc is wrong, and the reason why nobody's getting a plugged manifold anymore is because their EGR cooler is plugged up and impossible to recirculate exhaust?

Definitely a good argument about EGR and the MAF calculations. At idle after being 100% warmed up, my car reads 315 mg/str with EGR on, 530 mg/str with EGR off. That really doesn't make any sense to me. I did just clean my EGR valve, so it shouldn't be sticking, but I don't see any reason not to unplug the EGR valve vac line, put a golf tee in it, and see how that affects the MAF calculations? Also I'll also start looking at the actual MAF readings to figure this out, and not just spec/actual...
 

Nero Morg

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2003 Jetta wagon, 2001 Jetta TDI, 2014 Passat TDI
I keep my EGR because not only does it help with warmup, (even though there's a bunch of naysayers) it also helps reduce NOx emissions, which not only smells bad, it breaks down the ozone and has a long greenhouse effect. Something like 250+years.

At idle, it's not unusual for the maf actual to read less than maf specified, that's why it's a good test to do the hard pull in 3rd, because it creates a tremendous amount of air flow.

As for the cooler, either replace it, or block it off. That's your call. But a restricted egr cooler will actually lessen airflow to the valve, which would actually increase maf readings. If egr valve is open, it decreases maf readings. That's how the ecm knows if it's working. I still feel like the issue lies elsewhere.
 

oilhammer

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Dec 11, 2001
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outside St Louis (where it's safe)
TDI
There are just too many to list....
I clean EGR bits with a nice solvent we have. It works good. But it does take a while. A case of soaking, rinsing, soaking again, etc. multiple times. If the car starts/runs/drives, and it is your only car, I'd not be looking for things to fix like this. I have a nice clean EGR cooler I can ship you for cheap if you want one already cleaned. I probably have several.
 

runningallday

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Jul 22, 2017
Location
Iowa City, IA
TDI
1999.5 Jetta TDI manual
It's true that I should just keep driving it, not worth fixing something that's not broken. But I do have significantly worse mileage than I used to (maybe 10-20% worse), also it's kind of an interesting hobby to learn more about my car... I want it to go forever! :D I'm not going to be able to investigate further for a few weeks at least, too busy with other things, but it's definitely something I want to look into in the near future.
 
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