ALH blipping its own throttle? and limp mode??

vtpsd

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Aug 15, 2013
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03 jsw TDI, audi 90 AHU swap
My 03 wagon has a strange one. I started the car yesterday, and it rev'd up for a split second like I had my foot on the accelerator pedal (I did not). When I took off, I had boost, but only 10-12 psi. The car has a Malone stage 3 and runs 18psi normally.

Boost built normal, but the car never seemed to up the fuel and take off. Very little power. After driving it with my foot to the floor and making 12psi of boost for 30 seconds or so, it went into limp mode and fully opened the turbo vanes (I can hear it easily because of straight of pipe).

A restart will allow the turbo vanes to close and the turbo to make boost (but only 10-12 psi and not power at all). It has no more power with 10psi than it does with 0 psi. It is acting like the ECU is not adding any fuel whatsoever.

I did kick out code P1556 charge pressure negative deviation. I have not had a chance to get the VAGCOM on i it. I did a quick roadside test and the vac line to the turbo holds mouth vacuum, and I can move the vanes by sucking on the line. No obvious boost leaks.

Unplugging the MAF makes zero difference.

I did notice that my generic scan gauge registers 28-30" of HG when the boost gauge reads zero, and increases as the gauge moves up. I dont know if that readout is absolute or gauge pressure.

I am a bit stumped, I've had limp mode before, but not like this. Making half boost but zero power whatsoever!

It now does the automatic throttle blip about half the times I start the car, its quite obnoxious.

Any ideas?
 
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vtpsd

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03 jsw TDI, audi 90 AHU swap
What makes you think it is a pump? I doubt that the injection pump would work perfectly, and then 5 minutes later only be able to provide 20% power. It has never giving any kind of injection pump code. Only a charge pressure negative deviation code. Never any other signs of a wearing pump.

I have a spare 10mm and 11mm pump that I could swap in, but my diagnostic sense is not pointing to the pump at this point. It seems more like a MAP or MAF sensor issue, but I would think I would get a MAF code?
 
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vtpsd

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03 jsw TDI, audi 90 AHU swap
A little more searching has yielded other people having similar problems when the fuel cutoff solenoid sticks. They reported codes that pointed to the valve, I only have the low boost code.

I could be getting a low boost code because my car is so underfueled that it cannot build boost, but for some reason the valve is not tripping a code.

That is an easy swap with my spare pumps, I will report back.
 

UhOh

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And you've verified you have no boost leaks?
 

vtpsd

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Aug 15, 2013
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03 jsw TDI, audi 90 AHU swap
I am an hour form home without proper testing tools, based on what other boost leaks have felt like, i dont think it is a boost leak, however I cant verify until I drive it 40 miles home (at 40hp!)
 

\/\/0J0

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Sadly, none anymore
... I could be getting a low boost code because my car is so underfueled that it cannot build boost...
This is along the lines of what I was initially thinking when I read your post.

Barring some major obstruction in your air intake tract, I would say that you are experiencing a fueling related issue. Usually, the ecu is pretty good about throwing codes for pump malfunctions but not always.

Sent from my mobile look-at device
 

steve6

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May 25, 2010
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Beaverton, ON
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2003 jetta tdi
I am going to throw this in a different direction, the blip could be oil in the intercooler being sucked in, I used to get a slight rev up on start when I didn't do an Italian tune regularly.. and given random symptoms of turbo issues, I would be checking those items and your oil level.

Also, the ALh had about 60hp with no turbo, not 40 ;)

but also, did you fuel up recently?
 

vtpsd

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03 jsw TDI, audi 90 AHU swap
My car gets a hard Italian tune up every day, so no worries there.

I thought maybe I could dislodge the valve by rapidly cycling the key...and it seemed to work. No blip on startup, and full power and boost. Of course, there is no way to know it was the n109 valve that I freed when I cycled the key. I swapped the valve out with a spare when I got home and it's starting and running well. I can't call it fixed for sure, but maybe?
 
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vtpsd

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03 jsw TDI, audi 90 AHU swap
Ok, calling this fixed. It was the n109 fuel shutoff valve.

I think it has been not seating for a while and got worse over time. I noticed with the replacement valve, my starts are quite a bit more gentle than they have been.

Power is back to 100%. Low boost code was because the fuel was so chocked down by the valve presumably not opening, that the engine was not producing enough exhaust energy to make more than 10 psi of boost with vanes fully closed.
 
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