Author Topic: Losing boost - not sure where to look??  (Read 1517 times)

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zmaninco

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Losing boost - not sure where to look??
« on: June 06, 2006, 02:36:22 AM »
Hey folks,

On our 98 1.8T Passat, we are getting about 2.5-3 PSI of boost on heavy acceleration.

If we pinch the hose going to the wategate from the N75 - TAA DAA - 9 PSI of boost and lots of power.  I swapped in a known good N75 (thanx Ian!!!) but still get the same results - 2.5-3 PSI.  Pinch the hose, back up to 9 PSI.

All hoses have been checked out, so I think we are good there.  Very odd that pinching the hose provides plenty of boost.  I am not sure where to look next.  Seems like the N75 is the culprit, but replacing it yields the same result.

Any ideas???

Thanx!

Z

ColoradoB5

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Re: Losing boost - not sure where to look??
« Reply #1 on: June 22, 2006, 09:56:42 PM »
Well you changed the N75, but here are a few other things to check out.  Never tried the hose pinch technique, so I don't know if that would preclude these:

-Bypass valve (aka Diverter Valve or DV)
-Mass Airflow Sensor (MAF)
-Are you sure about the hoses? Have you replaced all of them?

Good luck!
You can't rehabilitate a fire ant.

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Re: Losing boost - not sure where to look??
« Reply #1 on: June 22, 2006, 09:56:42 PM »

gragravar

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Re: Losing boost - not sure where to look??
« Reply #2 on: June 22, 2006, 10:04:16 PM »
how about the hose connections.  when you pinch the hose you may be forcing a connection back together???

when you are not pinching the hose, do you hear any rushing air?  does slightly pinching it change the "tone" of the air such that you could locate the source of the sound?
Any man who can drive safely while kissing a pretty girl is simply not giving the kiss the attention it deserves.  ~Albert Einstein

zmaninco

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Re: Losing boost - not sure where to look??
« Reply #3 on: June 26, 2006, 03:39:00 AM »
Quick update for everyone.

It turns out the problem was a broken wire at the N75.  Fixed that and boost was back.

Thanx everyone!

Z

Usermanual

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Re: Losing boost - not sure where to look??
« Reply #4 on: June 26, 2006, 01:43:45 PM »
Can you give a quick description of how you came to this conclusion so if it happens to someone else we can use your diagnosis to see if the problem is the same?

Thanks.

zmaninco

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Re: Losing boost - not sure where to look??
« Reply #5 on: June 26, 2006, 02:33:49 PM »
Quote from: "Usermanual";p="48489"
Can you give a quick description of how you came to this conclusion so if it happens to someone else we can use your diagnosis to see if the problem is the same?

Thanks.


Sure.  Here is the quick rundown.  I was only getting 2.5-3 PSI of boost maximum.  I installed a boost gauge to monitor the boost.  All of the hoses were either replaced or confirmed to be in good condition.  This lead me to believe that pressure was being bled off somewhere, and pointed to the n75 and the wastegate.  I checked the rod on the wastegate on a cold car - it was rock solid.  Which typically means the wastegate is good.

I then looked at the n75.  A quick check is to pinch the hose going from the n75 to the wastegate - I used a small pair of visegrip needle nose pliers to do this.  I then went on a test drive and was getting 9 PSI easily.  Do not drive like this as it will overheat and overtax the turbo.  This is just a quick drive around the block.

I assumed the n75 was bad and borrowed a known good one from Ian.  Put it in and went for a test drive.  Getting the same 2.5-3 PSI.  Folks on PassatWorld indicated they had seen broken wires at the connection.  I then pulled back the rubber boot on the connector and sure enough, one of the wires was broken.  Spliced in a new wire, reconnected, and now fall into the 5-7 PSI range this engine should have.

In the future, I would try the pinch test first, and if that pointed to the n75, I would check the wires next.  Since this can be easily done without removing any other parts.

Z