ongoing boost problems with friends car

Ok. So here is the deal... again....
Car is 99.5 jetta.
about 125k on the odo
New n75

car throws cel, then eventually goes to limp mode.

cel reads:

17958 - Charge Pressure: Control Deviation
P1550 - 35 - 00 - -


The code sometimes says intermittent too.

Tonight I replaced ALL of the vac hoses, and replaced the EGR/antishudder valve assembly with a clean fresh unit. This did nothing, and the car still does the same thing. While changing the egr, I did see the obvious need to clean the intake, and I will be doing that.

Now, some more observations. While driving the car around for a test with the windows open, the turbo made a peculiar noise. Normally, when you floor it, and the car builds boost, and you let off really fast, you can hear the turbo spool down quickly, and it makes a quiet noise like, "PEEEeewwwwww......." that kinda trails off smoothly. Well, this car is making a noise like, "PEWEWewewewew......"trailing off. The intake is really clogged, and its my last stop before telling this guy he's gonna have to spring for a new turbo. Has anyone ever run into anything like this before?

Here's a shot of the intake.

and a shot of the egr that was replaced.


I'm wondering if the intake could be so clogged that its causing this CEL and boost deviation.

take a look at item # 7
Its listed as a check valve. Could this go bad and cause these issues? What are the symptoms if its bad, and how do I test it?

Poop, you need to check all the charge air hoses...i.e. anything post-compressor. Any air leak from the compressor to the intake will cause this exact problem. A loose hose, pin hole in a hose or intercooler, etc. And if the intake is severely clogged, that will only compound the problem. The turbo is compressing the air, but there is no place for the air to go since it cannot get into the engine unrestricted!

Usually since there is some oil from the breather system in the charge air hoses, an air leak will be accompanied by some oily stains. Check the "pancake tube" in the fender well first, then move on to the intercooler, and hose coming up from behind the headlight.

Hope this helps!

Also forgot to mention, the car has a fairly new Mercedes Pierburg MAF that seems to work fine, though I'll likely swap it out with a known good unit. Also, the intercooler and upper pipe is new. Only the pipe and hose between the turbo and intercooler is orriginal. I'll have them out next. I'm wondering if the internals of the vnt is worn causing overboost, or perhaps its just crud inside the turbo. Either way, this kid is broke and I'm trying to get him running properly for the least $$$.

take a look at item # 7
Its listed as a check valve. Could this go bad and cause these issues? What are the symptoms if its bad, and how do I test it?

Click to expand...

Testing is easy. It will flow easily when vacuum tested on one side, and will hold a vacuum when tested on the other side.

There was a post in the last few days where someone cleaned an oil-contaminated MAP sensor, and solved a boost problem. At least it's a cheap thing to try.

So i cant test it by with positive pressure right? It has to be vac? Because I was able to blow thru it either way. I'll try a vac source next time. What would the symptoms be if this check valve goes bad?

On that #7 part, at a past SFBA GTG a few months ago, FirstD, who doesn't post too much here anymore, had the problems you describe. He brought my spare N75 I had in my trunk, but decided to try and clean this #7 part you're referring to. He used canned air like one uses to clean computers and blew out that valve. He restalled the part and his car has run fine ever since. You might want to try that first...

I'll swap it out with the one from my car as a test. Part # is 046 905 291A
Would you believe IMPEX has the price listed for that little plastic POS as $64.10!!!!!!!!!!!!!!!!!!!

Ok, so I "checked" the black and white check valve (Item # 7 mentioned above) that is just to the left of the n75 and it was not working properly. I cleaned it out many many times with solvent and got a bunch of black gook out of it. The I lubed it up with WD40 and blew it out with air. It works like a champ now, only allowing air to pass one way. The car drives better, and we took it for a test drive. It seems able to drive for longer, and has more power, but still goes to limp mode after about 10 min of driving. This mind you is a significant improvement. I swapped the maf and it made no change. Intake comes off tuesday.

It may be a worthwhile thing for people to inspect that check-valve from time to time.

So item #7 is a check valve, but isn't item #10 also a check valve? I think I remember Velvetfoot healing someone's turbo by cleaning out that #10 check valve.

Don't thow out that Turbo!

Bring your car to VelvetFoot's garage first!

Click to expand...

earlier today I tried to find this thread using "VelvetFoot + Garage" in order to reference into this thread.

I think the date range eff'ed me.

Bring your car to VelvetFoot's garage first!

Click to expand...

earlier today I tried to find this thread using "VelvetFoot + Garage" in order to reference into this thread.

I think the date range eff'ed me.

Click to expand...

Found and bumped the thread your talking about. web page

Perhaps the cleaning of these 2 valves should be referenced in the FAQ regarding turbo issues?

Well, now I know why the activity on this thread!

take a look at item # 7
Its listed as a check valve. Could this go bad and cause these issues? What are the symptoms if its bad, and how do I test it?

Click to expand...

I having the same issues actually. Boost dissapears after a few minutes, turn car off then on and boost is back...somewhat. Got the positive control pressure deviation code too. I have silicone hoses coming and a N75 in the waiting. I did notice that the hose connected to the vacuum pump is extremely loose, even with that clamp on it. The hose which runs from the valve #10 to #11. Could i be loosing vacuum through that connection? I guess I kinda lucked out with this post, Thanks oldpoopie and VF too. I hope I have as good luck as you have had in solving your problem.

Dave

Dont I've got a spare n75 if you need to swap one out. The n75 is expensive and it would be a shame to buy one and have that not be the problem. pm me if you need it.

O/P, Thanks so much for the offer. This forum is great isn't it. I already have a new N75 which I bought right after I threw the 17965 (p1557) code but have yet to put it in. I'm going to replace all the vacuum lines, clean out the valves and put a band clamp on the hose where it connects to the vacuum pump. I'll save the N75.

So thanks for the offer. I'll just keep my fingers crossed that I get my turbo back.
BTW: you're dealing with code 17958 and mine is 17965. Do you know the difference and is it possible my solution is to be found elsewhere???


Dave

Ok. UPDATE:

Last night I pulled the intake and cleaned it. From the pics above it appeared very clogged, but when I pulled the intake it was only clogged like that at the opening, decreasing as it got deeper into the intake. The ports had almost no clogging. Also, the completely spotless EGR that I put on last week had a thick film on it already. Well, I put everything together, and started the car. It started normally.

Now here is the strange part

Then I wanted to see if I could disable the egr by blocking off the vac line to the valve. I placed a clamp on the valve, and when I did that the car would not rev properly. If I bliped the throttle quickly, the engine would sputter as it raised rpms, and would smoke like all get out. When the egr was re-enabled, it reved normally. I think that I'm on to something here, but I'm not sure where to look. I'll be removing and reinstalling the 2 egr-cooler flexi pipes tonight. I suspect that there may be a crack in one.

I should add that when the egr was disabled I saw some smoke from under the hood too......

Smoke normally says that the ECU 'thinks' it is getting boost and puts the correct amount of fuel in, but the engine is NOT getting the boost. Therefore, too much fuel and smoke. Maybe the EGR was open? This would allow the boost to 'escape' out the tailpipe and might account for this. Just my thoughts. Good luck!

Well, Today I replaced both egr flexi pipes with known good ones on the off chance that one was broken or cracked. It didnt help. Then I took off the hose that is immediately connected to the Vac Pump. It was full of crud. The hose includes a small check valve and then continues to the brake booster. I cleaned all of the hose out and got alot of stuff out. Then I removed the vac pump and cleaned that out too. there was alot of stuff in there. I opened up the vac pump to inspect, and saw that there was significant grooving around the inside perimiter of the pump. I was able to clean more crud from there as well. Anyway, I put it all back together and still no change. On top of it, the exhaust leak is still there. It must be coming from the downpipe flex area. Would a leak there cause a problem with boost? Also could it be a faulty N18 causing the boost issue, possibly allowing more exhaust gas into the intake than is supposed to be? The new egr that I put on last week had a supprising accumulation of soot already.

Ok, today I drove behind my friends car and it didnt smoke at all. Turbo was going fine. Then as I noticed a large puff of smoke, the car went limp. I think its the actuator on the turbo.... Replacing it with a spare tomorrow.

finally got it today. In a final attempt to fix the damn thing without removing the turbo, I took off the vac-actuator for the vnt. The vnt lever moved quite smoothly, but the vac-actuator was all screwy. It sounded like it had a bunch of stones inside it, and it was all corroded. I pressed it in and out and it crunched alot. Also, it got stuck in at one point. Thankfully, I had a spare actuator from my blown turbo, and I lubed that up and installed it. BINGO! No boost problems, no limp mode. Car drives as it should. FINALLY!!!!!!

Nice work Justin!

Nice job! It's good to see a problem talked about & then followed all the way to the end where it gets fixed.

I know you got the actuator from your old turbo... but has anyone found a source for these actuators new? I heard they weren't available by themselves but has anyone had any luck running down a supplier for these?

finally got it today. In a final attempt to fix the damn thing without removing the turbo, I took off the vac-actuator for the vnt. The vnt lever moved quite smoothly, but the vac-actuator was all screwy. It sounded like it had a bunch of stones inside it, and it was all corroded. I pressed it in and out and it crunched alot. Also, it got stuck in at one point. Thankfully, I had a spare actuator from my blown turbo, and I lubed that up and installed it. BINGO! No boost problems, no limp mode. Car drives as it should. FINALLY!!!!!!

Click to expand...

Nice work O/P, my results after removing my actuator were not as joyous. My lever gets jammed around 2mm or so before it hits the stop screw. My actuator actually works well and the return spring appears quite strong. I'm thinking of turning the screw up (it's pretty corroded)or puting a blob of JB weld on top of the stop screw to prevent the lever from traveling into the region where it jams.
I am however happy for you...really

Dave

finally got it today. In a final attempt to fix the damn thing without removing the turbo, I took off the vac-actuator for the vnt. The vnt lever moved quite smoothly, but the vac-actuator was all screwy. It sounded like it had a bunch of stones inside it, and it was all corroded. I pressed it in and out and it crunched alot. Also, it got stuck in at one point. Thankfully, I had a spare actuator from my blown turbo, and I lubed that up and installed it. BINGO! No boost problems, no limp mode. Car drives as it should. FINALLY!!!!!!

Click to expand...

Nice work O/P, my results after removing my actuator were not as joyous. My lever gets jammed around 2mm or so before it hits the stop screw. My actuator actually works well and the return spring appears quite strong. I'm thinking of turning the screw up (it's pretty corroded)or puting a blob of JB weld on top of the stop screw to prevent the lever from traveling into the region where it jams.
I am however happy for you...really

Dave

Click to expand...

Hmmm... When you had the actuator off, did you try just working the lever back and forth a whole lot, forcing it thru the sticking area? As far as the actuator itself, the car in question has been running without a bellypan or skirts for almost 80k. There was so much debris in the actuator, it jamed up. To all those who might experience a similar thing, with the actuator removed, place a vac source on the "nipple and retract the actuator as much as possible. Now tap the actuator on a firm surface over and over. When I did this I got a ton of flakey nasty stuff to come out. After I got as much out as possible, I poured a little motor oil down into the unit. Take the vac source off and work the actuator back and forth by hand. It gets much much smoother.

Oh, I should add, I got the motor oil on the actuator trick from member whitebelly.

Yeah, i worked the entire linkage for over an hour laying on my back. Spraying Wurth Rost off into the the lever area didn't seem to help with that one sticking point. when I d/c'd the actuator the rod had full travel in and out w/o any binding. I did it by hand as well as by drawing vacuum with a 50cc syringe. Like I said before, I think I may put a blob of JB weld on top of the limit screw for the time being until I can slowly scrounge up the cash to get a turbo.

Dave
BTW: how did you get the clip off? It's not like a normal cir-clip which you can use cir-clip pliers on.

Can you just turn the limit screw in to limit the travel of the VNT linkage? I imagine you would want to keep track of how many turns you put on the set screw so you could back it off to original condition later. I think this would limit the upper range of boost but if it keeps the turbo from overboosting & going into a limp mode it might be a decent temporary fix.

If I remember correctly, we did this with Betzel's Jetta when he was having boost problems at the New England Dyno Day two years ago.

Wouldn't motor oil have a bad effect on rubber over time? (Thinking there is a rubber diaphragm inside the actuator.)

KD, I'm not sure that fix worked. I'm thinking not, but I could be wrong.