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Discussion Starter #1
My 99 Passat with 65k JUST started acting up on the way home from work today. In 3rd and 4th gear at around 3k and higher at 80%-WOT the car seemed to rhythmically surge. I could hear the boost come up and then drop... come up... and then drop about every half second.

The car has an AWE K04 kit, GIAC programming, GreedSpeed FMIC and a Bailey DV.

Could a faulty or failing N75 be causing my surging? If not, what should I look out for? At lower boost levels, the car feels fine.

The odd thing is that this coincides with the installation of my 18" wheels. I had previously been running the 15" stock steelies with Blizzaks and would get wheelspin at the same throttle positions in 2nd. Now that I have 225 width Z rated rubber, the wheelspin is gone.

I'm really worried about my baby! I finally have some nice wheels and tires on the car and can finally push it and now this starts happening!
 

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Bump. I have been looking for a similar answer.
 

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Discussion Starter #3
Assuming it is the N75... which replacement valve is the way to go?

J or H?
 

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VaRiX said:
The odd thing is that this coincides with the installation of my 18" wheels. I had previously been running the 15" stock steelies with Blizzaks and would get wheelspin at the same throttle positions in 2nd. Now that I have 225 width Z rated rubber, the wheelspin is gone.

I'm really worried about my baby! I finally have some nice wheels and tires on the car and can finally push it and now this starts happening!
18" wheels will contribute to about additional 10 to 15% driveline loss, and your z-rated tires give you more grip on the road than when you had 15" wheels. Add both together and you'll get less wheel spin.

BTW, some vortexers have reported fixing surging problems with N75-J valve, but others have problem with soft limp mode with N75-J. However, you won't have to worry about Limp mode on your AEB.

I would just test it out, either H or J valve, since it only cost $65, and it is also one of those performance mods that few have been playing with lately with good results.
 

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The on/off/on/off/on/off boost is usually a bad DV. Looks like a sea serpent's back if you graph it from a vagcom datalog, but I know you can't log boost on an AEB. N75 changes can help with surging, but won't help with DV. Try switching in your old DV before you buy an N75, it's worth a shot.
 

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Discussion Starter #7
Thanks guys.

I am having the same problem. I have a big K04 and it occasionally will happen. I might try a new N75 one of these days.
Ahhh... that really sets me at ease! Thanks for the post. I was getting scared since I just bought the car. Shaggymatt was the previous owner, so I know it was meticulously maintained... but I was still concerned.

The on/off/on/off/on/off boost is usually a bad DV.
Could my Bailey DV really be bad already? I thought they were supposed to really last a long time... and handle higher boost levels.
 

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I have the same thing with mine, though I dont have a ko4, and my forge 007 dv is almost two months old. Is there a vacuum hose I missed somewhere. It only does it when i am not full throttle, at full throttle there is no problem, boost stays constant.
 

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Check all your hoses. My car had the on/off/on/off acceleration when I firt had the Oettinger chip fitted. I thought the DV was faulty and it turned out the zip-tie holding the vacuum hose in place had worn through the hose. This small leak was only noticable when the engine was under load and at higher RPM.
 
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