overboost

[peteguenther]

My Mk4 alh suffers occasional limpage usually on long hills with three passengers. Ive done the vac lines and cycled N75 with VAG Com. ( actuator works ) when I graph boost it seems always to spike then drop below expected then respike less - you may be able to see it in my photo gallery.
Is it Ok to manually activate and cycle the vanes and actuator with a wrench or something just to free things up in there? it seems the vanes cycle fully but not smoothly . Thanks

 

[STDOUBT]

It's fine to manually cycle the actuator, but you'll have an easier time of it if you disconnect the actuator arm from the vane arm side. Mind the circlip they tend to sproing away at high speed in random directions.
EDIT: you can do it by hand that way. You don't want to fight the diaphragm -especially with metal on metal leverage.

 

[wonneber]

I lost a few clips trying to get them back on.
Tie a piece of thread or floss to the clip so it's easier to find if it flies.

After I retired and the car was not getting it's daily Italian tune up I got limp mode a couple times.
I ran the car on the highway in 4th for about 20 miles (10 one way, 10 back) at 3000 RPM.

Seemed to help.

 

[ahldailydriver02]

I don't know the history of your car. How long have you had it? If its new to you then maybe the actuator was not installed with proper rod length. Also the turbo vanes maybe getting full of carbon, take it out and give it hell a few times to clean the turbo out, or try the Easy-Off oven cleaner method.

 

[wonneber]

I don't know the history of your car. How long have you had it?

If your replying to mine, I bought it new.
Replaced the actuator a few years ago & did the 3 & 19 inches adjustment.
Hoses & N75 a year or two ago.
Arm did have a slight sticky but working it seemed to clear it.

A while after retiring I got limp mode a few times & remembered a few posts quite a while back indicating to run it at higher RPMs on the road & it did seem to help.

 

[ahldailydriver02]

Yes sorry I was replying to you Wonneber.

Well maybe it just needs a good running at higher RPMs a few times or a good cleaning.

 

[peteguenther]

Ya the hi reves seem to help and i get plenty of that here in vermonts hills with no limp = its the long loaded pulls in fourth that trigger it when it happens

 

[Dhawk12]

OP have you checked that your actuator is holding vacuum? Mine was the same issue. Could drive it like I stole it and nothing, but pulling up a long hill would cause it to trip everytime. Checked and the actuator wasn't holding vacuum. Swapped it out, did the adjustments and no limp mode since.

Sent from my SM-N900W8 using Tapatalk

 

[wonneber]

There is a VW bulletin about the actuators rusting inside raising havoc.

 

[ahldailydriver02]

Agreed, get yourself a Mityvac and check the actuator. The actuator rod should start to move between 3-5 in.Hg and stop at 18 in.Hg and should be able to hold at 18. If its starts to drop after several seconds then your actuator is probably the culprit.

 

[BobnOH]

There is a VW bulletin about the actuators rusting inside raising havoc.

Almost makes me want to laugh. Most dealer repair companies would just replace the whole thing ($200+), just us little forum fishes discovered you can just replace the actuator.
Great idea for those symptoms, see if there's not a slow loss of vacuum in that line from N75 down to the turbo. It could be just the hose or the actuator is done. The actuator is an easy repair on the VE. If you loose the clip, a suitable replacement can be found at your local hardware.

 

[peteguenther]

Well that makes sense! Guess I'll have to break down and buy a mighty vac. below should be the link to boost graph:

 

[peteguenther]

hope it's ok that I am returning to this months later. So I bought a vac pump and found that the actuator appears to work fine and hold vac for minutes or more and I know that the N75 cycles the actuator and pretty sure at the time that I checked all that I checked adjustment of the rod and it's fine. all vac lines and the MAF are new too BUT still I get limp on long climbs and a few times I swear it's happened when iv'e barely got my foot in it. also I put in a crappy boost gauge and think I just caught it limping out once at about 12 psi.

So before I dig into cleaning the vanes I just want to see if any of you have further thoughts on this especially if you see anything in the linked photo of the v scope as it caught limp triggered. Does the MAP sensor ever go haywire? Thanks

http://pics.tdiclub.com/showphoto.php?photo=135548&title=boost&cat=500

 

[wonneber]

If the boost actual and requested difference is more then a certain amount for a certain time it triggers limp more.
So 12 psi actual could be to high if request is 10 psi (or so)

 

[Rrusse11]

Next step is clean the turbo, or replace.

 

[Tdijarhead]

I just did this to my 05. I was getting overboost on long hills. I checked my actuator and it was not holding vacuum, fortunately I had a spare actuator that I harvested from a blown turbo a couple of years ago. Since my turbo has 300k on it I pulled the turbo disassembled it and cleaned it replacing the actuator on the bench and properly adjusting it with a Mity vac.

Coolairvw has a you tube video on how to clean the turbo.


Over boost problem has been solved.