Still having issues with 98 Jetta TDI / Power Loss

Ok, I have been working on a problem that my 98 Jetta has for a couple years now and just can’t seem to pin point the problem. It isn’t a major issue, but occasionally just gets under my skin.

The car on long steep grades will drop into limp mode and lose power. If I cycle the ecm (key switch) and pop the clutch it will come right back to life.

I added a boost gauge recently and in town everything seems to be great. The car shows under hard acceleration a peak boost of 16-17 psi then drops off to 14-15. At cruising speed with a little headwind it shows around 4-5 psi. You wouldn’t know anything is wrong in town or normal highway driving. The pick up is great and for the most part the car seems normal.

My main concern at this point is that in conjunction with the boost gauge I installed a Dawes in parallel with the N-75. Around town or highway everything is fine and the boost is the same with or without the Dawes. However, now while climbing a steep grade I can only pull around 10 psi boost and it seems to continually (gradually) lose power even when shifting down and doesn’t seem to go into limp mode (no cel).

I seriously am at a loss with this car. I am going to take it up the canyon again today after work without the Dawes, and monitor the boost as it is stock, but am sure it will drop the turbo again.

What am I missing? Something has to be at the root of this problem…

Here is what I have done to this point.

-Cleaned the intake system, manifold, intercooler etc.
-Changed the hose from the intercooler hose to the ecm (twice now).
-Replaced ecu internal hose.
-Changed the n75 and all three hoses associated. (red, blue and black).
-Took the turbo off and was going to have it rebuilt but both reputable turbo shops I took it to checked it thoroughly and said there isn't anything wrong with it or the waste gate.
-Checked all the intercooler hoses for any leaks, cracks etc.
-Changed fuel filter.
-Changed air filter / removed snow screen.
-Installed Boost Gauge.
-Installed Dawes in Parallel with n-75.

Any words of advise would be greatly appreciated..

10q

Re: Still having issues with 98 Jetta TDI / Power

Sounds to me like slow fuel starvation. Since you've done all of the normal stuff (except check the MAF, and it's not likely with your situation) I'd next check the fuel sending unit. With a slight constriction, it might not be a problem in most cases, but with constant heavy fuel use (like up a hill) it might slow down the fuel enough to be noticed.

If you have vagcom, you may also test the MAF. I doubt that it's the problem, but since you're going "up the canyon" anyways....

Re: Still having issues with 98 Jetta TDI / Power

I guess I should have posted that I do have a vag com and the maf seems to be fine.

I considered fuel, but I noticed when I had it in for emission testing two months ago that when he really romped on it there seemed to be a good quantity of black smoke coming out of the tail pipe. Wouldn't that say there is an excess of fuel?

Re: Still having issues with 98 Jetta TDI / Power

If my theory turns out to be correct, you'd be able to get lots of fuel over a short period - but over the longer period, you'd run out.

Another test of this would be to draw it through the filter with your pela or some such - it should flow quite freely.

Lets go over this.
(1) your turbo works fine - usually. You've got power accellerating onto the freeway, and no problems with boost under most conditions.
(2) N75 is good, all vaccum hoses are good, the intake is good, intercooler is good - basically all of the "normal" problems do not appear to be problems at all.

You have a slow loss of boost, and of power, when going up a hill. Long hill if I'm not mistaken.

OK - another choice - the cat.

My money's on the cat.

Re: Still having issues with 98 Jetta TDI / Power

You are correct both the turbo and n-75...

Ok, luckily I had to run to one of our store locations this morning so I was able to test it on a grade without the dawes.

I was running 16 psi (steady) on a long grade and like flipping a switch the turbo just shut off and cel was thrown. I turned the ignition off and on, popped the clutch and all came back to life.

One thing I should mention is that I typically can baby the accelerator and not cause the problem, but when holding the pedal to the floor is when this problem typically happens. ie. If I back off the speed on a hill, then push the pedal to the floor (on a grade) it will typically happen with in 5-10 seconds.

The code again this morning was 00575 sporadic intake manifold pressure.

If it was a fuel issue, what would be my course of action? Are you thinking the pump needs rebuilt?

ps. the slow power loss was only when the dawes was installed in parallel with the N-75. With the dawes removed the power loss is instant.

I guess I may have to look at the cat (to my dismay). If it is the cat, where is the best place to buy one for a reasonable price?

Thanks for your input!

Re: Still having issues with 98 Jetta TDI / Power

If it's the fuel, I'd suspect either a bad filter (which you've changed recently) or some minor clogging at the fuel sender unit. This does seem to be the same symptoms as a filter going bad - could you have gotten some bad (dirty) fuel lately? Any biodiesel - sometimes a bad batch can mess up a filter quickly.

Some believe that the cat is not needed on our cars. However, it can be tested - and I wish I could find the thread telling how (something about testing the heat on each side of the cat when running - if there's a huge difference, then the cat is clogged - if the exhaust side is hot too, then it's not).

I haven't had to search for one, but you might try the "normal" places - tdiparts.com, worldimpex.com, etc. Perhaps someone else has a better resource at hand?

Re: Still having issues with 98 Jetta TDI / Power

"I was running 16 psi (steady) on a long grade and like flipping a switch the turbo just shut off and cel was thrown."

I had a similar problem with my Passat several years ago, and it turned out to be the waste gate actuator sticking, causing prolonged overbooost, and a CEL and "limp mode". Full power was restored after turning the key off and restarting the engine. The code was 00575, same as yours. The garage where I have servicing done freed up the waste gate and lubricated the linkage (heat riser lube?) and the problem has not recurred.

I note that you have already inspected the waste gate linkage, so my experience may not be germain. I have since installed a boost gauge, and in my experience 16 psi sustained is too high.

Since my problems were fixed, I have at least daily run flat out in 2nd or 3rd gear while observing the boost. If it goes to 15 or 16 psi and then drops to 12 or 13 everything is normal and I know that the waste gate is opening as it should. It hasn't happened (yet) that the boost stays at 16, but if it did, I beleive it would cause the limp mode phenomena.

None of this may be applicable to you, but it worked for me.

Doug

Curious. Which ecu do you have? I had that very same problem where my B4 wagon would be really fast some days and sluggish the next. Then superfast and limp mode shortly following. Same dtc. This happened more and more frequently till I chipped it. Then it never happened again. Odd? My ecu was an FA. It is now a GQ(spare). Food for thought.

It definitely could be the CAT, giving too much back pressure from being clogged up. If you have the time/energy/will to test it, you can hook up a pressure gauge before and after the cat (yes, some drilling involved, etc). Pressures should be close. Problem for me is that you have been chasing this for a few years.

In the past, a 575 code would one indication of a bad N75, but you replaced it from what I see.

Have you done any modifications to the car? Chip? injectors? Tuning box? Evry mod? Anything like that? As stated, your boost seems to be a little high, which indicates to me a boost leak somewhere. A boost leak can be done on purpose to raise boost, but if the ECM doesn't see more fuel going to the engine, it thinks something is wrong and goes into limp mode. Like you said, though, you seem to have replaced all the hoses, and inspected the intercooler lines.

Not really sure what to recommend, as you seem to have gone through it all. Only thing I can suggest is taking a look at the link in my sig. There will be a link in the first post detailing how to diagnose power issues on these cars. You may have gone through all of it without knowing, but it might give you a good read, and give you an idea of something else to check.

Re: Still having issues with 98 Jetta TDI / Power

There is the possibility that you replaced your N75 with a defective unit. Your symptoms sure sound like a bad N75 to me. 16 psi sustained is too high in stock trim. Snownut, do you have the opportunity to swap with a local club member for a "known good" N75, i.e. the one off his car that he drove in with?

Failing this maybe it's the wastegate. Hope all these two centses add up to a dollar for you.

Re: Still having issues with 98 Jetta TDI / Power

I don't but you may have a point. I suppose I could buy another N-75 and try it. Does anyone happen to have the actual Volkswagon number for it?

BTW, thanks everyone for your feedback!

Re: Still having issues with 98 Jetta TDI / Power

prior post

028906283F

This is for the A3/B4 tdis

Re: Still having issues with 98 Jetta TDI / Power

One more vote for the N75.

I just fought with this exact problem in my '97 Passat. It would run hard until it hit 80 mph on flat ground and then no boost - like flipping a switch. "This is the captain speaking - your power is now 60hp." I generally got an intermittent intake pressure error and sometimes intermittent boost code. Key off, key on, back to full power. I put hose clamps on the pressure lines to / from the N75 and pushed the limp mode from 80 to about 92. Installed a new N75 from Dieselgeek and no more trouble.

Re: Still having issues with 98 Jetta TDI / Power

I'm having the exact same problem it was diagnosed that the waste gate was seized open. we have changed it all out and now i'm still back at sqaure one. i have a the n75 fault happening too.

i have one question though when we ran the diagnostic on the system the n75 clicked the whole time even though in our mind it shouldn't have.

do you have this problem too?

Re: Still having issues with 98 Jetta TDI / Power

My n-75 does seem to click louder than it has in the past (continually). I ordered a new one and have it on the way. I guess I will have my answer when it gets here. ups tracking says I should have it on the 11th. I will keep everyone posted.

ps. the one I ordered is from Impex, I couldn't tell if it was oem or not, does anyone know? Has anyone had any experience with it if not?

Change over valve (Impex)

Re: Still having issues with 98 Jetta TDI / Power

When I got mine, it was OEM.

Re: Still having issues with 98 Jetta TDI / Power

please keep me updated cause my next theory stems to the computer its self and i don't wanna go there i have butterflys in my wallet these days

Re: Still having issues with 98 Jetta TDI / Power

Well, for the first update I did put a new N-75 in and my peak boost is now 14psi (down a couple). Tomorrow I should be able to find out what it does on hills...

Re: Still having issues with 98 Jetta TDI / Power

and the result was what

Re: Still having issues with 98 Jetta TDI / Power

My wife ended up taking the car but said the boost while climbing a grade stayed in the 10psi range. She didn't go up the canyon so I will have to do that this weekend.

Around town I noticed that after it warmed up (full op temp) I could get it to peak around 15 psi, but it would drop off to 10-12. Hopefully by Sunday I can give you the full scoop.

Re: Still having issues with 98 Jetta TDI / Power

Well, much to my dismay the new N-75 did not solve the problem. It seems that if my cruise control is on (80mph)and I am going up grades 6% or less it will hold around 13 psi and not have a problem. However, if I let out because of a vehicle in the way and start to accelerate again the boost will run 16-17 psi (continuous)and after a few seconds drops into limp mode.

So, what does that leave me? I suppose the Cat or something with the wastegate. I did check the wastegate before leaving yesterday and it was not sticking and seemed to be working fine.

One question though, I know that there was some oil in the wastegate diaphram when I had the turbo out last summer. I sucked all that I could out, but wonder if for some reason it is not allowing the wastegate to function fully. Any thoughts?

Thanks!

Re: Still having issues with 98 Jetta TDI / Power

I've been following this thread closely and I'd like to add a few comments:

1. The A-3/B-4 Turbo waste-gate is normally in the closed position and produces max boost untill the waste gate is "cracked" open to allow a reduction in boost pressure.

2. This air pressure to control the waste gate is tapped at the turbo air-charge outlet (the plumbing going to the inter-cooler)the fitting is screwed into the turbo outlet housing. One of the N-75 hoses is attached to this fitting.

3. The waste-gate nipple is where the other N-75 hose is attached.

What is happening in your situation is that your turbo is producing max boost (watse-gate is closed). The N-75 is cycling under the control of the ECU (as it should).But the water-gate is staying closed.

It is my opinion that you have an air leak.
The things I would check (closely) is the turo outlet nipple. Where the N-75 hose is attached (at the turbo outlet nipple. A leak at this location would not let enough pressure (to the N-75) to operate the waste-gate (keeping it closed).

You may want to remove this fitting and inspect it to see if it is cracked or maybe partially restricted.

One way that you can diagnose and confirm this theory is to remove the two "turbo hoses" from the N-75 and use a small union to join the two hoses. Doing this will open the wate-gate and KEEP it open producing ZERO boost.

If you do get boost you've found your problem...you have a leaking fitting!

A leak at this location wouild be very difficault to hear because of normal engine noise and the fact that it (the turbo out-let fitting) is in a recessed location.

The fitting that I'm talking about is the turbo out-let nipple. This is the source (or supply) air-pressure that opens your waste-gate.

We know that your turbo is prooducing boost...Your problem is not having the ability to control that boost. When the ECU sees this constant high boost it sends the signal to go into the limp mode.


This should be a simple and quick leak test. The only thing I would mention is to make sure that you no not mix-up the turbo hoses during the removal/re-connection. Perhaps mark them with tape to note which N-75 fitting they were attached to.

Re: Still having issues with 98 Jetta TDI / Power

ok, I hooked up the two turbo hoses and still had boost. I then took an air hose to the wastegate hose and I can't hear any airleaks (it holds pressure) and the wastegate is not opening. I can manually move the wastegate actuater, but the diaphram doesn't seem to be working. When I let off the air I can hear it gurgling inside the hose.

So now my question is can I purchase just the diaphram assembly (actuator) for my k3 turbo? And how exactly is oil getting into the diaphram?

Thank you everyone! I think between everyones (a few in particular) I am narrowing this down.

Re: Still having issues with 98 Jetta TDI / Power

ok, I hooked up the two turbo hoses and still had boost. I then took an air hose to the wastegate hose and I can't hear any airleaks (it holds pressure) and the wastegate is not opening. I can manually move the wastegate actuater, but the diaphram doesn't seem to be working. When I let off the air I can hear it gurgling inside the hose.

So now my question is can I purchase just the diaphram assembly (actuator) for my k3 turbo? And how exactly is oil getting into the diaphram?

Thank you everyone! I think between everyones (a few in particular) I am narrowing this down.

Click to expand...

At last you now have the problem isolated and you can make repairs.

You asked how the oil is getting into the turbo diaphram. This oil is coming from the CCV system.
As the hose from the CCV puck at the valve cover is routed to the turbo inlet. The oil is forced into the N-75 hoses right at the top of the turbo inlet. As the oily vapors are pulled out of the CCV puck they are drawn into the turbo hoses.
This is exactly why I've routed my CCV out-let with the external hose and just vented the CCV system over-board and fitted a cap onto the nipple where this hose attached to the turbo in-let duct.

The part number for the "pressure unit" is:028-145-716-A

Re: Still having issues with 98 Jetta TDI / Power

Thanks Herm, I am interested more in how you vented the ccv system. I think that's what I want to do.

Also, is that part number a Volkswagon number or 3k number?

Thanks!

Re: Still having issues with 98 Jetta TDI / Power

Thanks Herm, I am interested more in how you vented the ccv system. I think that's what I want to do. Also, is that part number a Volkswagon number or 3k number? Thanks!

Click to expand...

How I vented my CCV system was straight forward. I disconnected the small plastic flex hose from the CCV puck out-let and inserted a simple plug. Thne I attached a short section (2 Ft) of hose to the CCV puck out nipple and routed this behind the engine. I've never had any messy discharge or oil on my garage floor.

That part number is the VW P/N from ETKA.

Re: Still having issues with 98 Jetta TDI / Power

herm i've having the same problem however the car won't pull over 7 psi with a garret t45 knocks the car limp. 3 different turbos and same problem on all of them. there are no leaks on this system. changed the n75 valve and it seems to go a bit longer before going limp what are your thoughts on that?

edit: once the car hits 7psi it goes limp

Re: Still having issues with 98 Jetta TDI / Power

herm i've having the same problem however the car won't pull over 7 psi with a garret t45 knocks the car limp. 3 different turbos and same problem on all of them. there are no leaks on this system. changed the n75 valve and it seems to go a bit longer before going limp what are your thoughts on that?

edit: once the car hits 7psi it goes limp

Click to expand...

Ouch...three (3) turbo and an N-75

If your sure that the 4 hoses are all good (no leaks)

I'd be looking at the MAP sensor. This however means a new ECU. If you have access to another ECU that is what I would try as a means to isolate this isssue (MAP).

The reason I say this is:
The system drops in to limp mode meaning that the N-75 is cycling with the signal from the ECU (no N-75 related DTC). The Turbo is producing boost then the car goes into the limp mode. So the ECU/MAP is seeing the boost pressure that the turbo is pumping out.

One simple "test" you can try is this:
Using a common aquairaum air valve attached to the hose going to the ECU. Use this valve to "bleed-off" the signal air to the MAP sensor.
This will let the turbo develop full boost but the MAP will only see a little of the signal air. Be carefull doing this "test" because the turbo will be maxing the air charge (boost) to the engine.

If your TDI does not drop off into limp mode you've isolated the problem (bad MAP).

Re: Still having issues with 98 Jetta TDI / Power

I had the same problem with my 98 Jetta TDI. Last fall the dealer cleaned out the intake and the car ran flawlessly until one day in April then the CEI kept coming on and I had to cycle the key to get full power back. All they did this time around was clear the codes as the tech couldn't reproduce the problem during the test drive (Arrrgghhhh). I have a long hill on the way home that would always put the engine in Limp Home mode. All this started last spring after I put in the Upsolute chip, later I had the mufflerectomy done. I'm keeping my fingers crossed now that it doesn't start acting up again.

Re: Still having issues with 98 Jetta TDI / Power

i figured it out a small section of the intercooler piping had bubbled and was leaking and the only way i found it was when i went to put the tubing back on my finger broke through the tube and made a larger hole. the car now boosts a perfect 19 psi. thanks for all the info