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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old November 28th, 2017, 08:26   #1
ihredneck
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TDI(s): 2000 Jetta
Default Constant Low Power ALH

This only became 100% evident when my brother complained of my car's lack of power compared to his 02 with 5-speed.
This is not what I would consider limp mode because I had a MAF go bad and that was worse then what I'm experiencing now.

255k miles with original injectors and injector pump.

The car will accelerate decently but never really gets up and goes. Seems to be lacking on the top end but I can get the RPM's easily up to 4000+. I noticed the difference between our cars what seemed like after the turbo lag in all gears. Mine didn't really have turbo lag but performed ok and his definitely had lag then pressed me somewhat into the seat.
To be honest though we don't know if his car ever had any mods performed on it. He got it with an engine swap and that's the only history we know.

List of items checked/done:
-cleaned intake
-checked snow screen
-new air filter
-new fuel filter
-checked fuel pickup assembly
-verified n75 operational and swapped with n18
-VCDS logged actual vs requested boost and curves follow closely (max psi about 14 psi boost and holds)
-checked timing with VCDS
-hammer mod performed (no change)
-swapped MAF no difference
-wired open anti-shudder valve
-new vacuum hoses
-verified 23" vacuum post n75
-new stock cam/lifters
-MPG about 42 mpg with mixed driving
-turbo actuator moves freely


Ideas:
-catalytic converter plugged
-weak injection pump
-bad injectors

Any ideas on tests I can perform?

Thanks
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Old November 28th, 2017, 09:21   #2
indysoto
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Are you getting any black smoke? weak ip then?
intercooler cleaned(dunno if that would matter thou)?
Maybe a compression test??
Fill filter with diesel cetane additive run for a couple minutes shut down leave overnight?
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Old November 28th, 2017, 09:26   #3
bbexotics
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Bet egr valve and intake is full of carbon. Car can't breathe
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Old November 28th, 2017, 09:26   #4
ihredneck
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No black smoke that I can see in the mirror. A puff of blue on start up is all.

I had the intercooler out about 25k miles ago checking for oil accumulation, didn't flush only drained.

No compression test performed

Any preference on additive? Does Moly have something? I did perform a lubri moly diesel purge within the last 40k miles. I believe I ran two cans worth through the IP.
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Old November 28th, 2017, 09:27   #5
ihredneck
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Quote:
Originally Posted by bbexotics View Post
Bet egr valve and intake is full of carbon. Car can't breathe
That would be my first guess too, but has a new EGR and I cleaned the intake by scrapping and burning out the crud the way Frank suggested.
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Old November 28th, 2017, 10:33   #6
UhOh
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How were the intake ports in the head? (generally not as clogged as the intake runners get)

If vacuum is good and the actuator et al operate per spec then it's either an air or fuel restriction.

What's your timing like?

If one is really struggling with an engine's performance sometimes it's just a good idea to do a compression check.
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Old November 28th, 2017, 10:54   #7
ihredneck
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Head intake ports were very clean surprisingly, I have a record from previous owner showing the intake had been cleaned before.

I believe I have the timing set at just above the blue line on VCDS . I will need to verify though.

Planning to perform a compression test this week, maybe tonight.
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Old November 29th, 2017, 04:44   #8
ihredneck
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Confirmed timing is between 48-50, just below the blue line. I am trying to get IQ requested to match IQ actual.

Now got to locate a compression tester that will fit, thought I had access to one but no go.
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Old November 29th, 2017, 08:18   #9
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(via hermtdi)'Sounds like you have isolated your problem to a leak elsewhere in the vacumm system. Most likely a hose worn or one of the plastic unions / "T's" in the system. most likely the long vac hose that goes down to the turbo actuator.

One more thing (last thought). Look at the center line (mid car) on the fire wall.
There is a "Y" type fitting. Check this fitting to see if all three (3) hoses are connected.'

worth a shot, good luck!
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Old November 29th, 2017, 08:45   #10
ihredneck
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indysoto,
I'm not sure how you were able to determine it is a vacuum leak issue?
I know boost holds at max psi and doesn't fall off so I don't appear to be having issues with vacuum to the actuator.

Can you please explain?
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Old November 29th, 2017, 09:33   #11
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Quote:
Originally Posted by ihredneck View Post
indysoto,
I'm not sure how you were able to determine it is a vacuum leak issue?
I know boost holds at max psi and doesn't fall off so I don't appear to be having issues with vacuum to the actuator.

Can you please explain?
Sorry thought you had just checked the actuator and not from the top, I had copy and pasted from another forum post, so sounds like you already elimiated that.
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Old November 29th, 2017, 09:40   #12
ihredneck
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Okay thanks for clearing That up.

Found a compression tester so will get it tested here soon and should be able to report back.
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Old November 29th, 2017, 19:07   #13
wonneber
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Quote:
Originally Posted by ihredneck View Post
I'm not sure how you were able to determine it is a vacuum leak issue?
I know boost holds at max psi and doesn't fall off so I don't appear to be having issues with vacuum to the actuator.
When you say 'boost holds at max psi and doesn't fall off' are you saying going down a flat highway you have 15 pounds of boost all the time?
I mostly have 3 to 5 pounds normally. I have a mechanical gauge tapped into the intake.
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Old November 30th, 2017, 05:11   #14
ihredneck
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The boost holds at max psi when I'm accelerating up a hill or putting a load on the engine.

It holds constant also for cruising speed. Probably right about 3-5 psi via VCDS.
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Old November 30th, 2017, 14:16   #15
wonneber
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Quote:
Originally Posted by ihredneck View Post
The boost holds at max psi when I'm accelerating up a hill or putting a load on the engine.

It holds constant also for cruising speed. Probably right about 3-5 psi via VCDS.
OK, that sounds better.
Mine gets up from 10 to 13 pounds (or so) on inclines.
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