Narrowing down low power causes

2000alhVW · Sep 9, 2018

My car has suffered from low power for a long time.
The symptoms are.... no power. That's it. No noticeable black smoke or soot (it does smell a bit strong though), and no obvious issues. Someone like my mother could drive the car indefinitely with no complains other than "its VERY slow". Very hard to trip a DTC. When it does trip, it is P1556.
I have a VCDS. At very low throttle, the car does okay. And the measured vs actual MAF values stay kinda close. Anything more than 20% throttle, and they deviate wildly. When increasing throttle, the actual MAF reading will decrease. I read an article on KermaTDI that might answer why - when the computer senses an underboost issue occurring, it cuts back fuel. So basically, as I try to increase throttle, the computer cuts even more power.
Things I've done:

Replaced MAF. Bought new Bosch MAF off eBay. zero change. I also grabbed an unknown MAF (OEM Bosch) from the junkyard and put that in. Zero change.
Unplugged MAF - trips "MAF ground fault" CEL, and regains some power
Replaced all vacuum lines with quality material from IDparts
Swapped my N75 valve with N18 valve, zero change. Went to junkyard, grabbed unknown N75 & N18 valves, swapped them in, zero change.
Vacuum tested the system and determined it properly holds vacuum. I have applied vacuum to the actuator (w/MityVac) and confirmed actuator rod movement. I did not measure the movement to confirm 3inHg-18inHg.
Visually examined my intake manifold. Very little buildup on the walls.
Replaced fuel filter.

At this point, I feel like my issues are narrowed down to an actuator, turbo vanes, or a boost leak.
If I'm missing something, please correct me so I can add it to the list of things to check.
I plan on doing the easiest thing first, which is spraying the actuator with WD40 and then looking more closely at it. After that, I feel like the easiest thing is to check for boost leaks.
Is it possible to do a sort of at-home smoke test?

WildChild80 · Sep 9, 2018

I had a boost leak and it was the elbow at the intake right on the bottom

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2000alhVW · Sep 9, 2018

The rubber hose that goes right to the ASV?

WildChild80 · Sep 9, 2018

Yup

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burn_your_money · Sep 9, 2018

It's not uncommon for the air duct for the intercooler to rub through the very bottom of the intercooler and cause a leak.

2000alhVW · Sep 10, 2018

Thanks for the replies. I am investigating possible boost leaks. Is there a way to 'get at' the intercooler without removing my bumper or similar? I looked through the slats on my bumper and saw the right half of my intercooler fins seem to be packed with black gunk...

I read that one of the signs of a boost leak is oil residue on the outside of the pipe. I'm feeling kinda defeated and confused since I'm finding oil residue all over my engine in odd places.

Should I investigate these areas any deeper?

Also, how bad does my actuator look? I've been trying to test it repeatedly with a hand pump.

I'm trying to get better access to the actuator, and I want to remove the plastic tubing that goes from the accordion'd intake tube (that clamps to the MAF) down to the turbo. It is supposed to have 2 bolts, one on the I/M and the other on the block. Is this pipe one piece or does it come apart half way?

WildChild80 · Sep 10, 2018

The bumper cover comes off so easy, the first time is scary but after you get it off you'll laugh. The hardest part is that clip for the hood pull.

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2000alhVW · Sep 10, 2018

WildChild80 said:
The bumper cover comes off so easy, the first time is scary but after you get it off you'll laugh. The hardest part is that clip for the hood pull.

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You were absolutely correct!

2000alhVW · Sep 10, 2018

Got the bumper off and now have an up-close view of my intercooler.

Things may be looking a little hairy at this point.
Methinks it caught a rock and has a hole.
Can someone confirm this?

2000alhVW · Sep 10, 2018

WildChild80 · Sep 10, 2018

Was this a northern car? The actuator doesn't look like a prom queen but doesn't look terrible from what I can see. Have you hooked your vacuum pump directly to the actuator and watch how much vacuum it takes to move it and how far it moves?

Have you driven with the windows down and every noise maker turned off and listen for a noticeable hissing?

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BobnOH · Sep 10, 2018

Looks like an old car to me, don't see any reason that thing isn't still intercooling just fine.
Back at Post #1

2000alhVW said:
..............At this point, I feel like my issues are narrowed down to an actuator, turbo vanes, or a boost leak..........................

Seems accurate.
What does the actuator do? Are the vanes free? I've seen some creative methods for diagnosing boost leaks.

WildChild80 · Sep 10, 2018

BobnOH said:
Looks like an old car to me, don't see any reason that thing isn't still intercooling just fine.
Back at Post #1

Seems accurate.
What does the actuator do? Are the vanes free? I've seen some creative methods for diagnosing boost leaks.

I'm still working on something to blow enough vacation volume to see, hear or feel it...still at the drawing board

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2000alhVW · Sep 10, 2018

WildChild80 said:
Was this a northern car? The actuator doesn't look like a prom queen but doesn't look terrible from what I can see. Have you hooked your vacuum pump directly to the actuator and watch how much vacuum it takes to move it and how far it moves?

Have you driven with the windows down and every noise maker turned off and listen for a noticeable hissing?

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Not northern, per se. I bought it from Western MD, but the car is actually in really, really good condition considering. Aside from flaking clear coat, the body is actually mint. Spotless rockers and such. For being a 2000, it actually looks remarkable in terms of rusted fasteners.

I have hooked a vacuum pump up to the line that plugs into the N75. It holds vacuum indefinitely. I think I have possibly found a flaw, but it's still mentally blurry to me. I confirmed the lever starts moving at ~3inHg, but I can't tell if it stops moving around ~13 or not. It seems to move a large distance with each additional pump until ~13in, but after 13, I can't tell if it advances and stays, or advances and then slides back to it's previous position. I'll get under it and look more closely.

BobnOH said:
Looks like an old car to me, don't see any reason that thing isn't still intercooling just fine.
Back at Post #1

Seems accurate.
What does the actuator do? Are the vanes free? I've seen some creative methods for diagnosing boost leaks.

I'm just suspicious of the localized oil junk. The left half of the intercooler looks pretty good, but the right half almost looks like it got a pinhole in the middle and has been spitting oil.

Have not looked into the turbo at all. Is there some way to see the vanes without a lot of disassembly?

WildChild80 · Sep 10, 2018

Unfortunately the only way to see the vanes is to split the turbo unless you can see them with a mirror with the down pipe off...just not easy period

Use some brake clean and wash the intercooler and see if the gunk comes back or wet it down with water and dish soap and see if it blows bubbles

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2000alhVW · Sep 10, 2018

I saw someone post a trick to try to listen for boost leaks. It was posted in terms of a manual trans - "E-brake on, foot firmly on brake pedal, put the car in first gear, and partially engage the clutch at 1500rpm in order for the engine to build boost and apply a load." I assume the process is similar for an auto trans. Put it in gear and rev the engine with the brakes engage.

I like the idea, but the issue is I only have my girlfriend as a helper. It's not that I don't trust her, but I wouldn't want an accident to happen while I've got my ear next to the intercooler. Do you think it would work if the motor was idling, and I engaged the actuator with a hand pump to adjust the turbo vanes to produce boost?

WildChild80 · Sep 10, 2018

You might get away with it but I'd want to see how much actual boost it was making...it'll probably throw a code

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2000alhVW · Sep 10, 2018

WildChild80 said:
Use some brake clean and wash the intercooler and see if the gunk comes back or wet it down with water and dish soap and see if it blows bubbles

I like it.

WildChild80 said:
You might get away with it but I'd want to see how much actual boost it was making...it'll probably throw a code

I have no real measure of boost anyway. I have VCDS, and the "actual boost" reading offers no help.
Additionally, I've determined this motor/ECU system is pretty dumb and it's hard to trip a code. I think the only time I got it to spit out a useful code is after 300 miles of driving. 300 miles of zero boost driving... IMO, I would think a car should trip a code within 30 seconds or so of such a large problem being present.

WildChild80 · Sep 10, 2018

If not faster

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BobnOH · Sep 10, 2018

2000alhVW said:
.........................
Additionally, I've determined this motor/ECU system is pretty dumb and it's hard to trip a code. I think the only time I got it to spit out a useful code is after 300 miles of driving. 300 miles of zero boost driving... IMO, I would think a car should trip a code within 30 seconds or so of such a large problem being present.

The ODBII accessible stuff is pretty dumb. It does offer clues and allows us to measure certain specific things, pretty helpful all in all. But there is no replacement for mechanic level knowledge. I'd stick with the tried and true troubleshooting guides found here and at myturbodiesel.com.
I read a lot here at these forums and see many low power/limp complaints with anecdotal and even random testing of components to no real conclusions.

WildChild80 · Sep 10, 2018

OBDII is miles ahead of OBDI and the on or off reading...

If you pulled on the actuator with vacuum it might make some boost... shouldn't make enough to damage anything...

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2000alhVW · Sep 10, 2018

Well spent another 4 hours dicking with it.
Took the front bumper off. Inspected the intercooler. Removed the plastic tube to the turbo, checked that for cracks. I pulled and released the actuator several times while spraying it with WD-40. It pulls and releases smoothly. I visually confirmed it hits the stop at an indicated ~16-17inHg. But my gauge may be off.
I checked the rubber hose from the upper intercooler pipe to the I/M. Looks great.
Had my GF rev it to 1500 in gear. I didn’t hear or feel anything suspicious in the plumbing.

I also visually inspected the rest of the plumbing from above and below the car.
The compressor side fins of my turbo look good FWIW.

At this point, I think it’s either turbo or plumbing leak.
Also, what is the likihood I’m having a fuel delivery or ign timing issue? Also also, now that I think about it, is it possible there’s a cam timing issue?? I bought the car as a “limp mode project” and it has a sticker saying TB replacement done ~10k miles ago. Could be one tooth off?

I know absolutely zero about fueling data in VCDS, but the IQ numbers still look odd to me.

WildChild80 · Sep 10, 2018

8 mile lake used to sale cam lock tools on Amazon, pull the vacuum pump and lock the cam with the 2 lobes for cylinder 1 in the more up position and see what the tq converter shows.

Did you check the function of your vacuum pump?

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WildChild80 · Sep 10, 2018

You can move your IP until the graph in vcds shows good but the program is assuming you have cam/crank timing spot on. From my experience, if it won't start with everything at zero then there is a problem. I had a bad cam lock tool and had to fight my first timing belt job and I actually lost the tool and bought a complete kit with the same tool but this one worked differently in that it was snug in the cam slot. Then I saw that my timing was off and since using that tool, every belt I do starts up first time every time.

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2000alhVW · Sep 10, 2018

I think someone making a mistake on the last timing belt job was kind of wishful thinking on my part. Wishing the fix would be that easy.

The truth is, I’m pretty sure the motor runs flawlessly. Easiest starting motor I’ve ever seen. Idles flawlessly. And motor sounds fine under acceleration...it’s just not getting what it needs to make power.

wonneber · Sep 11, 2018

2000alhVW said:
I like it.
I have no real measure of boost anyway. I have VCDS, and the "actual boost" reading offers no help.

Here's a link to read: http://www.ross-tech.com/vag-com/cars/tdi.html

It does display requested and actual boost.
If the 2 numbers are to far apart you have an issue.

Logging boost, mass air flow and N75 percentage driving 25 mph and flooring it to 50 mph (shifting as needed) usually displays what the gurus' need to look at.

2000alhVW · Sep 11, 2018

wonneber said:
Here's a link to read: http://www.ross-tech.com/vag-com/cars/tdi.html
It does display requested and actual boost.
If the 2 numbers are to far apart you have an issue.
Logging boost, mass air flow and N75 percentage driving 25 mph and flooring it to 50 mph (shifting as needed) usually displays what the gurus' need to look at.

Thanks for the post. It means a lot.
The actual vs requested boost do deviate similar to my actual vs requested MAF readings, but not as severely, I think.
Here's a picture for reference

I will confirm this weekend when I'm back with the car. For now, just doing a lot of digging to compile a list of possible causes and things to check.

eddieleephd · Sep 12, 2018

Try pressure testing the boost system.
https://www.myturbodiesel.com/wiki/boost-leak-tester-leaking-turbo-symptoms-how-to-fix/
And you should go to the Malone tuning website and upload logs to and from there.
They're easier to see and observe what's up.

Pictures don't have the functionality of the graphing Malone employs.

It's much easier than using Excel to graph them.

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2000alhVW · Sep 13, 2018

eddieleephd said:
Try pressure testing the boost system.
https://www.myturbodiesel.com/wiki/boost-leak-tester-leaking-turbo-symptoms-how-to-fix/
And you should go to the Malone tuning website and upload logs to and from there.
They're easier to see and observe what's up.

Pictures don't have the functionality of the graphing Malone employs.

It's much easier than using Excel to graph them.

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Thanks for the advice. I'll tinker around with this next time I'm cataloging.

I've been convinced to give the intake manifold a thorough look. I'm good with wrenching, so I'm okay with taking the whole thing off and cleaning it up even if it isn't very clogged.

Question: when removing the I/M, do I need new gaskets? Or is it okay to re-use the old ones?

Picture for reference (my car btw):

wonneber · Sep 14, 2018

2000alhVW said:
Question: when removing the I/M, do I need new gaskets? Or is it okay to re-use the old ones?[/B]
QUOTE]
New gasket.
I could have reused mine as it came off intact but did not want to take a chance.

Also, you should replace the o-ring between the EGR valve and the manifold.

Narrowing down low power causes

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