[passat]

Hello, newish member here, timing belt completed no problem thanks to excellent info on this site.

This 1Z passat has limp mode since I got it , I have traced down a bunch of air intake leaks, power is better but it still goes into limp mode, it does "reset" when I turn car off and then back on. I have replaced the fuel filter, the little hose inside the ecu, most of the other hoses, cleaned the intake/egr valve, done a leak test, replaced the intake pipe section with a hose with hose clamps because the original was cracking. No error codes, and never has check engine light.

N75, when I drive with this electrically disconected, the car has much reduced power, almost like limp mode but not quite. How is the car supposed to be with this disconnected???

The car does no go into limp mode when I disconnect the N75 but it has wau less power than the car does before it goes into limp.

This is my first question with regards to limp mode.

 

[Seatman]

Hi, your car wont go into limp mode with the n75 disconected because it wont over boost. The n75 controls the vacumn to the actuator for the turbo, have a look at the limp mode faq and you should find all your answers there.

http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm

 

[chittychittybangbang]

Common mistake seatman, on your car the N75 controls vacuum. On his car it does not have a VNT so it controls pressure.

Either way, the N75 controls turbo boost. No n75 means you'll get minimum boost. I'm not sure but I would think it would throw a code.

"No error codes" this means the car has had a full scan with VCDS right?

 

[Seatman]

Lol I presumed his car did have a vnt whereas mine doesn't, I have a waste gate. Is there a faq on the wastegate type turbo or is it just the vnt one?

 

[passat]

My car is 1996 canadian 1Z passat station wagon, 5-spd manual. 418,000 km

turbo is a waste-gate style.

It makes sense that with the N75 electrically disconnected I get very minimal boost. This is what happens to my car. Does this result then tell me that my N75 is okay?

It has not had a vcds scan, only a generic obd-11 scan, the only error code it ever had was to do with me removing the 5-th injector solenoid, whoops. I solved that code by wiring in a 10 ohm- 10 watt? resistor( a big square thing ). I would have just put the redundant solenoid back in but I had left it in a town 800 miles behind.

What is a good way for a mac computer owner to work with vcds.
Can I make my own vcds cable with my relatively useless obd-11 scanner cable?
Any VCDS people out there in Vancouver Island,, hello.........Thanks for all your expert consideration.

 

[Sipper]

Could you have another fueling restriction? Maybe the wiring to the N75 is bad? Just a guess?

 

[passat]

I do not think the wiring to the N75 is bad because when I purposefully disconnect it there is such a clear difference , that returns to "normal" as soon as I reconnect.

I have changed the fuel filter in the engine bay. Are you suggesting there is a filter or pickup tube in the tank that could require attention?

How would I go about checking fuel flow.... It seems until I get a proper VCDS anaylsis I am out of luck. When I manage this I will reply. Any advice on how to make your own VCDS would be very interesting.

 

[chittychittybangbang]

You can buy a cheap cable on ebay but it can't run the full version software. It will run older VCDS software freeware but to have all functions you have to buy the software license which is not transferable which means resale is almost nothing. IMHO, it's cheaper in the long run to buy a genuine cable and resell it when you're done, the license follows the cable.

In the trunk or rear seat there's the other end of the fuel line where the fuel tank level sensor is. Remove it and check that all ports are clean and tight, not restricted. Worst case you could have something growing in the tank and causing goo to clog it. I am not sure if this would cause limp mode though, mostly low power by restricting fuel. Limp mode is often caused by something related to turbo control or sensors.

 

[Seatman]

I was just reading your post again and was just wondering have you made sure the waste gate isn't sticking at all as that is what happened on my car. I took my turbo off and gave it a good clean which sorted everything out.

 

[vwnut]

They were bad to fill the wastegate can with oil. N75 can't open the wastegate .. overboosts and goes into limp mode.

 

[Seatman]

They were bad to fill the wastegate can with oil. N75 can't open the wastegate .. overboosts and goes into limp mode.

How can that happen?

 

[audi1z]

Hi,

N75 can't open the wastegate .. overboosts and goes into limp mode.

N75 does not open the wastegate. With N75 passive (disconnected), the wastegate is controlled by the intake pressure acting on the boost pressure control actuator, which opens the wastegate with increasing pressure. With N75 active (pulse width modulation from the ECU), the pressure acting on the boost pressure control actuator is reduced, and opening of the wastegate is shifted to higher intake pressure levels. Accordingly, an active N75 prevents from opening the wastegate.
Going into limp mode with N75 active may result from two different error conditions
- intake manifold pressure control range error (in other words intake pressure too low compared to air mass flow, because of a leak)
- intake pressure too high.
You need a read out of your ECU for further troubleshooting.
With N75 disconnected, you have a reduced boost pressure, but the engine should still provide about 70% - 80% of its nominal power. When you drive "full power" in the 3rd or 4th gear in this mode, does limp mode occur then?
Regards

 

[passat]

I am about to have time again to work on cars limping again. I will try to get a proper engine code scan it town. I will also do another boost leak check and drive with full power no N75 again before reposting. Thanks for all the advice.

 

[passat]

Limp mode solved

Well I finally solved my limp mode issue, and without a vagcom, but that would have been way easier I suppose. It was the N75, so I believe it was overboosting. The bad N75 makes a clicking sound!

Prior to diagnosing the N75 I removed, lubed, and adjusted the wastegate actuator mechanism, replaced a lot of air leaks, multiple boost leak checks, repaired a cracked main plastic turbo intake pipe with a section of marine hose and high quality hose clamps, which seals very well.

So one thing I found is that my old N75 was making a clicking sound when I would turn the car ignition on, but not yet start the car. The new N75 does not make this sound so that could be a helpful diagnosing trick for some people. The car was limping before the old N75 was clicking, but after replacing the N75 I have full power. It is worth the effort to fix the limp!

I have also replaced recently all the shocks and every single rubber bushing on the suspension including the rear axle bushings. I have a couple pictures and helpful hints if anyone is interested?

 

[chittychittybangbang]

Sure, any pics and tips are useful. If they're not in the FAQ than they can get added.

FYI, lots of good mk3 type N75 rapidly click before you turn the key on and before you start the engine. The solenoid is rapidly turning on-off. In your case it was bad but the clicking is not a 100% sign that it's bad. I don't know why they do that and as you have noted, many don't click.