Volkswagen Passat Forum banner

1 - 20 of 29 Posts

·
Registered
Joined
·
2,418 Posts
Discussion Starter #1
Here is my issue you guys!

I thought it was a freak occurance, but I was wrong.

Last night after installing my 28mm rear sway, I took a nice corner filled drive to really evaluate performace.

I took a wide sweeping curve @ 30 mph in second gear, after the curve came to it's apex I shifted into third and mashed the petal.

Well, nothing happened. I got exactly 1 lb of boost, and all naturally aspirated power. I couldn't reproduce it later that day no matter what I tried.

This morning I was doing some regular driving, and I shifted into 3rd @ 35 or so m.p.h. again NOTHING HAPPEND. I released the gas, and floored it. Same thing. nothing. I down shifted into second @ 30mph, and lit up my boostgauge and layed some rubber.

WHAT IN THE HELL IS HAPPENING?

It couldn't be a hose/DV/Valve issue, the boost simply isn't being "requested" by the computer.

Kelly suggested I swap stock chips for a couple days and see if it happens. So I just did a few hours ago, and although I can't reproduce it, I can't say I'm enjoying 7lbs of boost spiking at 13. :cry: :mad:
 

·
Registered
Joined
·
1,926 Posts
bump for more info
how many miles, maybe your turbo went or a seal around your turbo that causes it to loose boost periodically, but i dont that it would be all or nothing like that. ask kelly is she would reprogram your chip to rule that out, if stock doesn't repete same results
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #4
Oh how I wish I had a VAG-com!

You'd think I'd have one by now but I don't have a laptop either! thats a BIG $$$ start up fee, so don't I just feel like the ass! Would I get a CEL from that code? I'm all clear as far as MIL go...

...So I guess I should say

It SEEMS like the computer isn't communicating with the turbo. I checked all the typical hoses and connections, I took apart and reoiled my DV about 200 miles ago...

The only other insight I can say is that I had all my stored codes cleared (random multiple misfire and CAT below efficiency) about 20 minutes before this happened by my mechanic.
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #5
jeffsu350 said:
bump for more info
how many miles, maybe your turbo went or a seal around your turbo that causes it to loose boost periodically, but i dont that it would be all or nothing like that. ask kelly is she would reprogram your chip to rule that out, if stock doesn't repete same results
I've got 25k on the car 10k has been chipped.

You're right, it IS all or nothing. Unfortunatly for me, there is no way I can "check" any seals around the turbo/manifolds.

I'm going to drive with the stock chip for three days. I have a dyno appointment on sunday, so if by then I havn't repeated the problem, I'll have Kelly re-prog the chip.

THANK YOU FOR YOUR EFFORTS SO FAR!
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #6
Just talked to my mechanic and he's never heard of this problem! (D'oh)
He said its a "fluke" but I'm worried because it's never happened before, and now it happened twice in two days!
 

·
Lisa Simpson
Joined
·
15,044 Posts
This is a job for VAGALOG!

I wish I was closer, I would lend you the machine so you could log some blocks to find the problem. I am suspicious of an electrical fault that is not in the chip. Keep poking around under the hood. 1psi of boost is still boost, and that means something is happening.

The fact that repeated throttle openings fix it tells me that it is not the chip.
 

·
Registered
Joined
·
541 Posts
Yea I serious doubt it was caused by a chip. Are you making this even occur at some g-force level? If so is it possible that you are sucking air into the fuel pump?
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #11
Natski - No turbo spool at all, and believe me, I can hear mine. The loss of pressure only happened those two times.

Kathy - Thank you for the reponse. My worst fear is that its something electrical, which means I probably can't fix it myself. I wouldn't know where to begin "logging blocks" to narrow it down. I think I'll have to take it in to the dreaded dealer, and I bet you a coke that if there arn't any fault codes logged in the memory, they'll be clueless, and won't be able to reproduce the problem.
I'm leaning twords your idea that it isn't the chip because its such a random problem. What MECHANICAL problem (harness/wires) could cause the chip to "not respond" after 10K miles of driving? Nothing!

VWGuy - ECU harness was good to go when I disconnected it to put in the stock chip. But I wish the problem was that easy.

LIVE4SPD - I don't think I'm sucking air into the fuel pump because when I mashed the petal I DID get some acceleration, just not "boosted" acceleration, not to mention it was a STEADY pull (albeit slow) and no sputtering. The motor was just working without the turbo.

Its like the car "forgot" it was a turbo for a second, then after I switched gears, its like it "remembered"!
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #13
atomicalex said:
Boost control circuit. I think it's the N75 valve? If it were sticky, then you could have a loss of the loop feedback. Potential problem. :crazy:
Good idea. Now, should I take off the "race" N75 "J" valve, clean it/blow on it then replace it, or just put the stock one back on?

I think I'll put my chip back in, and disect the N75 and inspect it...and re-install it.

Thanks Kathy!
 

·
Registered
Joined
·
3,341 Posts
this is a good idea, try the stock n75 valve, you might be getting an overboost spike with the race valve causing the ECU to kill boost.

This is kinda evident if you say you are spiking to 13 psi on the stock tuning, god know how much you are spiking with the chip! :nervous:
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #15
Scotty, remember that the N75 "J" valve bumps up the STOCK boost about 2-3psi!
Which sounds about right. If I put the stock N75 valve back in, I'll only be spiking around 9-10psi (stock form) I'm sure of it.

My question to you is, if indeed the ECU is killing the boost because of an overboost spike, why now? This is the first time in thousands of rough miles!?!

Oh, BTW-my boost spikes are scary, My gauge only goes to 20, and that gets burried quite often! :weirdo:

Time for a bigger turbo with less boostage, eh?
 

·
Registered
Joined
·
3,184 Posts
Could it be your traction control kicked in?
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #17
not_too_shabby said:
Could it be your traction control kicked in?
Hey, that COULD be it! (NOT) :shock:

No mang, the traction control was OFF, as it always is!

I know the symptoms of a full throttle run when the traction control is on quite nicely. (it "cuts" power in a different way than what I was experiencing)

But those two times I mashed the throttle, NOTHING happened, no turbo whine, no Boost gauge LEDs no power! It only *reset* itself when I switched gears.

Thanks for your "help" :wink:
(I'm just busting your chops, thanks for the bump)


On a serious note, I took apart the N75 valve area and I have a question...
Does your Pressure regulator supposed to have oil in it? Well, mine does...
 

·
Registered
Joined
·
3,341 Posts
Spanky McGee said:
Scotty, remember that the N75 "J" valve bumps up the STOCK boost about 2-3psi!
Which sounds about right. If I put the stock N75 valve back in, I'll only be spiking around 9-10psi (stock form) I'm sure of it.

My question to you is, if indeed the ECU is killing the boost because of an overboost spike, why now? This is the first time in thousands of rough miles!?!

Oh, BTW-my boost spikes are scary, My gauge only goes to 20, and that gets burried quite often! :weirdo:

Time for a bigger turbo with less boostage, eh?
Yeah I know it bumps boost a bit, but if its failing it might be way-overboosting. try the stock N-75 :thumbup:
 

·
Registered
Joined
·
2,418 Posts
Discussion Starter #19
Yeah I know it bumps boost a bit, but if its failing it might be way-overboosting. try the stock N-75 :thumbup:
I will try that. thanks!

One last question though, if indeed the N75J valve is overboosting, wouldn't power be shut off AFTER a high-spike, and not right when I change gears? Does that make sense to you?

:thumbup:
 

·
Registered
Joined
·
1,512 Posts
Spanky McGee said:
Yeah I know it bumps boost a bit, but if its failing it might be way-overboosting. try the stock N-75 :thumbup:
I will try that. thanks!

One last question though, if indeed the N75J valve is overboosting, wouldn't power be shut off AFTER a high-spike, and not right when I change gears? Does that make sense to you?

:thumbup:
In the accused event, power will shut off during WOT, which happens in mostly higher gears (3/4/5). I think the shut off point is around 23/24 psi to hit soft limp mode, so if you're not peaking near there, then look else where.

I would check into DV related vacuum lines and such and make sure DV valve itself isn't sticking.
BTW, if your n75 valve is shot, then you'll get default boost around 4-7 psi.
 
1 - 20 of 29 Posts
About this Discussion
28 Replies
12 Participants
x
Volkswagen Passat Forum
Passatworld is a forum dedicated to Volkswagen Passat enthusiasts to discuss mods, Quattro, Turbo Diesel, reviews and more!
Full Forum Listing
Top