N75 failed again?

[Metalnerd]

About a year or more ago, (~50 K miles ago) I had the power loss after sustained boost. Per suggestions from Mickey or GoFaster, I swapped out the signal hoses and the N75. Not sure which worked, I did both to fix it ASAP (Poor Scientific approach, two variables, confounded)

Well, this morning, after some "spirited" driving up the mountain, the same thing happened. Sustained max boost triggers a whimpy mode that goes away when the car is shut off and restarted. I can trigger it often.

I will put fresh hoses on this weekend.

Do those N75s have a limited life span?

I may check the signal hose inside the ECU box, as a last resort.

Any other suggestions?

BTW - The car is unmodified

 

[dogbreath]

Go after the hose inside the ECU first Chuck, not last. The hose walls weaken and collapse- your spirited driving could have definately KO'd this little bugger.

 

[Metalnerd]

OK,I will check that first - thanks for the shoe-to-rear motivation.

 

[Metalnerd]

We tore into the ECU tonight. The air tube inside the box looked to be in excellent condition. My ECU was replaced about 4 years ago under the smoke recall.

I changed the signal hose from the plenum to the ECU for good measure (again).

I DID find the EGR hose broken wide open.

Will that cause my power loss? /images/graemlins/confused.gif

Test drove it for 30 miles in a "spirited" fashion with no problems. Tomorrow I will try the mountain again.

 

[Metalnerd]

The old gal beat the mountain this morning. No problems.

EGR vacuum hose?

 

[Weasle543]

Is it throwing a CEL? If so did you check to see what the code was? Sounds like it's going into an overboost condition.

Broken EGR hose would be a vacuum leak? N75 wouldn't have any vacuum available to control the waste gate? If so, what's the wastegate's position with no vacuum full closed or open? Full open=underboost Full closed=overboost

Just my guess.

 

[20ValveT]

VAG-COM has an output test for the N75. Why don't you try that before you condem it.

 

[Metalnerd]

Thanks. Good pointers.

No CEL.

 

[John Beyer]

I think the N75 valves get dirty and stuck more than fail. You'll get a stored fault before the light goes on but it sure sounds like overboost.

Also, the wastegate actuator works on pressure from the turbo not vacuum.

Good Luck

 

[Metalnerd]

Flogged the mountain again /images/graemlins/smile.gif

Check those brittle hoses. I gotta market some good hoses.
Thanks
-Rubbernerd

 

[Metalnerd]

That B4 is still misbehaving.

Now I notice surging under max load above 2500 RPM. The limp mode returned too. It is surely an overboost problem because it runs very strong before limping out.

Don't have a lot of time to fart around with my buddy's vag-com, it is sometimes easier to replace a couple high risk parts.

Do you guys clean the N75 out with something?

 

[BKmetz]

Carb cleaner works good, anything that can dissolve carbon.

Brian, 97 Passat TDI

 

[Metalnerd]

Thanks. I will poke around a bit.

 

[Grabaman]

Metalnerd: I've had the same issue..replaced N75 and vac hoses - all was good for a while (a few 1000 miles). Now it seems that if it's hot (>90) and I'm climbing a steep grade, I get limp mode. No CEL (and I don't own VAGCOM and don't live near an Autozone)...I've been thinking slowly failing MAF...what do you think of that hyptothesis?

Thanks for posting your experience/data...helps the rest of us work through it!

thanks, graba

 

[Metalnerd]

Well....... I replaced about 5 yards of pressure & vacuum hose with no change. Cleaned the N75 with plastic-safe contact cleaner - no change.

Bought the N75, swapped it out and the problem is GONE.

That last one only lasted about 45K (I think, can't find exact records)

Will try the mountain tomorrow to be sure but very smooth to 4000 rpm driving locally.

Thanks for all the help!

 

[pfowler]

where is the N75 I HAVE LOOK IN VW BOOKS AND TRIED TO FIND WHERE THIS ITEM/ RELAY IS AND I HAVE NO CLUE...
PLEASE SOME ONE TELL ME WHERE I CAN FIND THIS PART ON MY 98 JETTA TDI <font color="blue"> </font> PFOWLER@BRAINGEARS.COM

 

[Metalnerd]

Follow the small red and and blue hoses from the turbo up to the firewall area. They both meet at the N75 valve.

On Passats, they are direcly above the power brake diaphram. It is held in place by two rubber posts and has 3 hoses attached to it and one small electrical connector.

 

[tomo366]

On the the Jetta it is the same valve used on the Passat but it mounted on the right front between the air filter and the fuel filter

 

[paramedick]

Tomo is correct. It is held on to the inner fender liner by two little rubber "nipples". Just pull on them gently, and it comes off.

One warning. The red, blue, and black hoses are secured with metal surround fasteners. You must carefully cut these off before removing the hoses from the N75. I recommend cutting the hoses from the N75. The little plastic nipples become fragile. Don't ask how I know this. /images/graemlins/blush.gif /images/graemlins/frown.gif

If you need the N75, IMPEX has them.

Part number: 028906283F Change Over Valve for Vehicles With Accelerator Pedal -Electronic Module
Price: $52.30 Quantity: 1 Total: $52.30