sudden loss of boost in 2002 Jetta

hugho

Active member
Joined
Feb 17, 2018
Location
NW wyoming
TDI
red 2002 vw Jetta wagon 250K miles, MT
While driving back to Wyoming from Idaho yesterday I pulled out to pass and punched it and suddenly lost power and had to pull back in. ***? I noticed 0 boost and then negative vacuum on my recently installed gauge. Very slow trip home, down to 15-20 mph at times on the passes. Went straight to TDI club forum when I got home and discovered "limp mode". Turned the car back on and my turbo is back of course. All new to me. I have an old MB Diesel and a 12V Cummins and assorted tractors without any modes but wide open balls to the wall! Mine is a neglected 2002 5 spd wagon with 250K miles which I have brought back to life in the past 6 months with a Malone 2 and new injectors and it has run perfectly, very fast and 50 mpg. Iv'e done all the usual fixes and maintenance like manifold cleaning, egr fix etc and this set me back emotionally. I see that there are many possible causes but my question is what is the MOST LIKELY CAUSE given the limp mode was triggered by trying to pass in 5th gear? So far I have just checked the vacuum tube to the actuator. Hooked up and visually OK. Actuator seems to move freely. This has never happened before and I have done a lot of throttle punching so what is the most likely cause and what checks should be done in sequence? I hate throwing new parts just to see what happens. I am starting to lose my love for this car because this is a very dangerous problem.
 

flee

Veteran Member
Joined
Sep 19, 2011
Location
Chatsworth, CA
TDI
2002 Jetta GLS wagon
Read Canadian_Grizzly's thread on limp mode if you haven't already.
Easiest and cheapest place to start (assuming no VCDS) is to replace the 16+ year
old vacuum hoses. There are two sizes and a trusted vendor can supply them both.
Check the brake vacuum booster hose very carefully as these are known culprits.
A 'free' check is to be sure the snow screen is clean and/or just remove it.
Obviously check or replace the air filter.
 

hugho

Active member
Joined
Feb 17, 2018
Location
NW wyoming
TDI
red 2002 vw Jetta wagon 250K miles, MT
thank you. I finally found Canadian Grizzly's great post. I will replace all the hoses as you suggest.
 

williambill

Veteran Member
Joined
Dec 15, 2013
Location
Dry Prong, LA
TDI
2002 Jetta TDI
I had same issue with my bone stock jetta a while back. Falling into limp mode on hard pulls with a soft over boost code. I checked all hoses (they were new), checked for leaks, swapped N75 with N18, vane movement, no change. I made the problem go away by "de-tuning" my turbo actuator. I adjusted it a couple threads in the direction that requires more vacuum to max out (sorry, can't recall if that is shortening or lengthening the rod). I think before, the arm on the turbo was hitting the stop at 16", now it hits at 18". I figured maybe due to wear on the actuator ring over time or some other factor, the turbo produced to much boost, but IDK. Anyways, it solved my problem. Maybe it's something to look at.
 

hugho

Active member
Joined
Feb 17, 2018
Location
NW wyoming
TDI
red 2002 vw Jetta wagon 250K miles, MT
Read Canadian_Grizzly's thread on limp mode if you haven't already.
Easiest and cheapest place to start (assuming no VCDS) is to replace the 16+ year
old vacuum hoses. There are two sizes and a trusted vendor can supply them both.
Check the brake vacuum booster hose very carefully as these are known culprits.
A 'free' check is to be sure the snow screen is clean and/or just remove it.
Obviously check or replace the air filter.
WELL MY SAGA OF LIMPING ALONG IN LIMP MODE CONTINUES... Canadian Grizzly has an excellent post and I have been working thru the checklist. First off the car came with AT injectors, .158 orifice and previous owner ditched the crappy AT and put in a 5 spd. I sent the computer off to Cascade German and they did a malone 2. With the old AT injectors the engine ran OK but had a wee bit of smoke. No limp mode problems. I put in a set of used low mile MT injectors and had the IQ set by the dealer. It was after this work that I got limp mode but the car ran much better with more power and seemingly better economy. The vacuum hoses seem new and I checked every connection. all tight. Vacuum at the N75 was poor, 8mm when it should have been 25 or so. BTW I have never kicked any codes. It was 8mm directly out of the vacuum pump also. The inlet fitting would twist and had a wee bit of wobble so I smeared it with silicone and clamped it back on. Vacuum was now 18-20 at the inlet and the N75. Much better but not 25mm hg. I headed up Teton pass and it ran like a scalded cat until I topped out at 60 and put it in 5th gear and BAM, limp mode. What is next? I am starting to hate this stupid vacuum modulated boost. My other cars , a MB turbo diesel and my cummins pickups have mechanical wastegates. Also I cannot get my egt over 700 no matter how hard I thrash it and it runs 350-500 deg at 60-65 mph. These egt temps seem low. Can I get rid of the vacuum modulated boost and replace it with a mechanical control?
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
What is next is diagnosis. We can only do so much via this interweb thing.
Diagnose each component, using proper method, one at a time. You will find the problem. Keep it simple, avoid paying too much attention to all the anecdotal information in the 100s of posts we have. There are good instructions here and at myturbodiesel.
This user contributed Search Engine may help.
Use the input box near the center left.
 

KrashDH

Top Post Dawg
Joined
Dec 22, 2013
Location
Washington
TDI
2002 Golf
The inlet fitting would twist and had a wee bit of wobble so I smeared it with silicone and clamped it back on. Vacuum was now 18-20 at the inlet and the N75. Much better but not 25mm hg.

A lot to read through but here's my documentation of boost issues:

http://forums.tdiclub.com/showthread.php?t=490188

There was a mention of checking the hose going from the pump to the booster, but unless you're having braking issues that's likely not the culprit.

You said the hoses "seem" good, but they can get small slices in them, even the plastic T's can develop minor cracks. You said that RTV on the vac pump nipple brought you better vacuum numbers, but that 18-20 is still low.

You never mentioned how long it took you to build that amount of vacuum. A good working pump should build 25-30 all day, within seconds if you're connected directly to the pump, or the small nipple on the inline check valve on the brake booster line.

Mine would build 25+, but it took about 40 seconds to get there. It wasn't pulling enough vacuum to support the system. That's after I roll peened the edge of the nipple over so it didn't spin or move anymore, AND rtv'd the connection.

If you've verified that your N75 and N18 are holding vac as they should, as well as the ying-yang check valve, then I would say that your pump may be the issue and it's time to bite the bullet. The reservoir stores vac to supply both of those check valves as well, so if that's leaking and your pump can't keep up, it could be the culprit.

Hope you get it figured out, post back results when you resolve
 

flee

Veteran Member
Joined
Sep 19, 2011
Location
Chatsworth, CA
TDI
2002 Jetta GLS wagon
WELL MY SAGA OF LIMPING ALONG IN LIMP MODE CONTINUES... (edit) Also I cannot get my egt over 700 no matter how hard I thrash it and it runs 350-500 deg at 60-65 mph. These egt temps seem low.(edit)
Where is your EGT probe situated?
 

hugho

Active member
Joined
Feb 17, 2018
Location
NW wyoming
TDI
red 2002 vw Jetta wagon 250K miles, MT
A lot to read through but here's my documentation of boost issues:

http://forums.tdiclub.com/showthread.php?t=490188

There was a mention of checking the hose going from the pump to the booster, but unless you're having braking issues that's likely not the culprit.

You said the hoses "seem" good, but they can get small slices in them, even the plastic T's can develop minor cracks. You said that RTV on the vac pump nipple brought you better vacuum numbers, but that 18-20 is still low.

You never mentioned how long it took you to build that amount of vacuum. A good working pump should build 25-30 all day, within seconds if you're connected directly to the pump, or the small nipple on the inline check valve on the brake booster line.

Mine would build 25+, but it took about 40 seconds to get there. It wasn't pulling enough vacuum to support the system. That's after I roll peened the edge of the nipple over so it didn't spin or move anymore, AND rtv'd the connection.

If you've verified that your N75 and N18 are holding vac as they should, as well as the ying-yang check valve, then I would say that your pump may be the issue and it's time to bite the bullet. The reservoir stores vac to supply both of those check valves as well, so if that's leaking and your pump can't keep up, it could be the culprit.

Hope you get it figured out, post back results when you resolve
Thank you for your thoughts. When I checked the vacuum directly out of the nipple, I got 8. very low. After RTV I got 18-20. No more.I concede that hoses downstream of the pump might have leaks but I doubt it. I checked others and they seemed around 18. There are no brake issues. I think I may have to live with 18-20 in case it is the pump or the gaskets. There are good features with these cars but there is a lot of complexity amd maintenance issues. I bought this car because it could get 50 mpg and the day is not far off when a car that can get high economy will be very valuable if oil becomes scarce or expensive. I have a MT corolla with 300K miles which gets 41-50 mpg and a MB 240 D which gets 32-36 mpg and both are dead simple durable designs.
 

steve6

Veteran Member
Joined
May 25, 2010
Location
Beaverton, ON
TDI
2003 jetta tdi
Is it happening constantly now? Could be sticky vanes, bad actuator etc.

If just every so often until you figure out the issue _________Safely________ learn to turn off/on key while rolling and it will bring back boost without having to pull over every time to turn it off/on.
 
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