Sudden loss of power on 96 Passat

On the way to work today after pulling a few big hills like normal, the car developed a lack of power. Low end torque seems to be acceptable but high end craps out. No CEL when it happened. Will restart at lunchtime today and see if I get any lights.

From the information posted previously by our club brethren, I assume the following:

In order of most probable:
1) Mass air flow (MAF) sensor
2) Clogged intake or fuel filter
3) Obstructed exhaust (have had a bad rear muffler rumble for weeks now).

I am leaning towards numbers 1 or 3 due to the sudden nature of the event.

112k mi. on the odo and original MAF. K&N air filter for about 20K mi.

Any opinions?



[ May 20, 2002, 06:19: Message edited by: Metalnerd ]

Have you tried it since? I once had a sudden loss in power. I turned the car off, turned it back on, and never had any issues again.

Betcha there's a leak in the hose from the intake manifold to the ECU!

It also sounds like a N-75 selenoid sticking.

That is exactly how my car acted when my N-75 selenoid stuck open, loss of power above 2500 RPM.

Brian, 97 Passat TDI

Thanks guys.

I took her out for some spirited driving at lunch. Seems to be running strong!

Smells like a sticking N75 solenoid? No?

A quick peek at the braid coverd hoses - they seem fine. I should consider freshening the hoses at next maint. interval. I had one braided hose go bad before(the one that runs between the battery and the inner fender)

I will be going over the mountains on the way home too. That should be an interesting test too.

Thanks again,

- Chuck

If the power came back but leaves on the hills I would try the cheap hose to the ecu first, as GF mentioned.

The old gal ran strong all the way home.

We will try the mountain again tomorrow morning......

Hi Guys, I would be more inclined to believe that it is either a vacuum hose in the N75 changeover valve system being plugged or leaking or the N75 valve itself. The N75 valve can click till the cows come home during a Vag-com output test and still not be operating properly mechanically. I have been known to be wrong once or twice however. Later!

[ May 20, 2002, 19:16: Message edited by: Harvieux ]

Here is the latest in the riddle.

Drove 50 miles home last night, cruise control on and off. Mountains, the whole bit. No problems. Drove locally last night – No Problems

Drove to work again this morning: The mountains were no problem, got onto expressway and the first 18 miles were no problem with cruise. About 2 miles from my destination: same loss of power in the same stretch of road!

The loss of power occurs after clipping along on cruise and going down a long (2 or 3 mile) grade, full coasting. When the road levels off and starts up the next hill, the car’s power is reduced (barely holds 60 mph under cruise and slowly degrades) and from that point onward, acts like it has no top end. Even local driving after that point is affected.

Shutting the cruise off does not help. Resting at a traffic light while running does not help. Tapping on the N74 solenoid while idling has no effect.

Shutting the car off and immediately restarting – eliminates the problem. I did, however, notice a slight lag and surge around 3000-3500 rpm that was never there originally.

Here is my logic: Not throttle position sensor because it occurs under cruise.
Not a clogged fuel filter or suction problem because idling does not help.
Not a mechanically stuck wastegate because shutting the car off fixes it immediately.

May not be a stuck N74 solenoid because tapping it hard with a tool when idling does not help (??)

Seems to be electronic because shut down and immediate restart restores power.

Tonight I will start replacing signal hoses.

Wadda you guys think? Smelling more like N74 or the MAF?

Why does coasting after driving 45+ miles trigger it? Still no Check Engine Lights.

nerd, Your symtom's are almost exactly like mine were. I bought vacuum hoses and checked out the price of N75's, but first I cleaned my intake. Problem solved.

My problem also had a sudden onset...when the intake was so clogged that it started driveability problems at speed on the highway.

Thanks ALKO.

The goofy thing is it runs extremely strong except for this glitch. If it was dogging it most of the time, I too would suspect the intake manifold.

Metalnerd, Like I mentioned above, it's your vacuum lines to and fro N75 or N75 valve itself. It is not your MAF,fuel filter,speed sensor,or throttle position sensor. The giveaway is the fact it resets after shutdown and restart. If I'm not mistaken, and since you do use this vehicle for off-road use only, I think a CCV by-pass mod will pretty much prevent this PIA problem from future occurance. Later!

[ May 21, 2002, 08:28: Message edited by: Harvieux ]

Thanks Harvieux! I will freshen up some hoses tonight. I will get a price on the N75 while I am at it.

Don't forget the hose from intake manifold to ECU, that's the one that gave my car this symptom until I replaced it. The rubber hardens up over time and they leak at the end fittings.

Hmmm. It goes bad when it hits a certain location, eh? Sounds like a case for Fox Mulder. Aliens? Secret government electromagnetic testing? A weakening of the fabric of the universe?

In my case the permanent fix was to eliminate the N75 and replace it with
http://www.dawesdevices.com. This mechanical boost controller is
almost half the discount price of a new N75, which I guarantee will fail
in the same way again.
Plus the dawes device will actually improve performance when u adjust the
boost to 12lbs which is within safe engine operation.

and on the third day he obeyed GoFaster and his club brethren.

And this morning NO POWER LOSS.

Monday Power Loss
Tuesday Power Loss
Tuesday Night, Change Manifold to ECU hose and trimmed the end of hose that attaches near the vacuum pump. (the mini-hose that attaches nearest to the engine) for a sample of tube gauge (it did look a little shaky).
Wednesday No Problem

Not statistically correct but trending in the right direction! Will keep you posted.

I ordered a new N75 valve - probably swap out all hoses and N75 this weekend to be sure.

Thursday - NO Problem!

Go Baby Go!

Mike...

One question....which of the dawes device did you buy to replace your N-75 controller valve?

Thank you
Herm

THis one:
http://www.dawesdevices.com./boost.html

I plumbed the Dawes device inline in place of N75 and capped
the 3rd line to N75 from the intake.

I left the N75 plugged in electrically so I do not get a CEL.
I used a metal fish tank valve from PetsMart #73725707141,
4 bux, on the ECU sense line to bleed a little pressure off to
keep the ECU happy. I have a boost gauge and adjusted the
Dawes for 12lbs peak. Mine's a 98 Tdi with 101,000 miles.

Originally posted by mike:
THis one:
I plumbed the Dawes device inline in place of N75 and capped
the 3rd line to N75 from the intake.

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">Mike, since you have completed this mod, what differences do you detect??

thanks.

Mike..
Thank you for your responce...one more request...Can you E-mail me a photo or 2 of your set up. I'd like to see how you have the vacumm routed and the general installation.

Herm...

Hi Gang, Wanted to say what a great call GoFaster made on the vacuum line from the intake manifold to the ECM. I now have a new wrinkle on the brain for diagnosis. Later!

Harvieux:

You got mail somewhere.

Shoupsr

Thank you for all your help.

I hope that I can return the favor sometime!

Thanks shoupsr, I emailed Beowulf for the correction. Later!