-
AAZ Low boost problem - symptoms & final solution
by
Otis2
on 23 Nov, 2005 15:03
-
I wanted to give a 'heads up' to anyone who is following Smog's "Fast AAZ" mod list from the FAQ, who is having trouble getting adequate boost from their K14 turbo. Took me 9 months to figure out the [trivial] cause, so I write this long post in hope of saving someone similar frustration.
"Cut To the Chase" version: make sure the locknuts on the threaded wastegate actuator rod are at the EXTREME end of the rod. It is only the last 1/4" or less of the threads that make any useful improvement on boost pressure from a K14. If you want a solid 15 psi to build up fast from these turbos, then go even farther with the locknuts than the photo in the Smog FAQ shows (which looks already to be within a couple of threads of the end of the rod).
Ok, now the long version, symptoms & diagnosis:
Symptoms:
I thought I had done the Smog mods properly, but I was always disappointed with my boost pressure. It climbed to 10 psi relatively quickly, but anything after that would take a full throttle run, at full load, and high rpms. I became convinced that the AAZ with stock K14 turbo simply would not build over 12 psi of boost, except for sometimes wavering at 12 psi for a second or two at most, at nearly 4000 rpm, and then dropping back to 10 or 11 psi.
I tried installing a boost bleed in the vaccuum hose between the turbo compressor housing and the wastegate diaphram can, but the boost bleed had little effect. I even blocked this hose off altogether with a golf T, so the wastegate would never get a pressure signal, but nothing changed. This really surprised me, because the very same bleed device in the wastegate hose had already allowed me to increase the boost on a gasoline-powered turbo Volvo from 8 to 14 psi. The bleed achieved this increase in the Volvo with zero other mods. So by comparison, the VW turbodiesel engine had me baffled.
I read other people's experience here on GTD with their own boost pressure, and people here would talk about data points like 14 psi at 1700 rpm, and I would think, "What the heck are they doing different? That's impossible!"
Solution:
I asked for help in another thread here, and it was suggested that I was underfuelled. "You need fuel to get boost". So I turned up the main fueling screw about 1/4 turn until I was getting a noticeable improvement in torque, but also great clouds of black smoke under low rpm/high load conditions.
With the main fueling screw turned up, maximum boost pressure did improve a bit, by 1 or 2 psi, so that I could then see boost up as high as 13 or 14 psi, but again, only under full throttle, full load, high rpm conditions. And again, the rate of boost pressure would build really slowly after hitting about 9 or 10 psi, and only when the revs built over 3000 or 3200 rpm or so, in 3rd or 4th gear (Vanagon 4-speed trans).
I reported back that increased fueling had solved the problem. But actually, it simply masked the problem.
The real issue turned out to be my failure to unscrew the locknuts on the threaded wastgate acutator rod, to a sufficient position towards the end of the threads.
I had put my locknuts to about where the photo on the Smog FAQ shows them -- more or less at the end of the threads, but with the nuts maybe one or two threads in from the end of the rod, just for what I thought was enough "thread meat" to secure them tightly.
Yesterday, after a suggestion from Dave (935Racer - thank you!) to look at the wastegate, I experimented by moving the locknuts to the EXTREME end of the threads. The "outside" locknut is now about half a thread BEYOND the end of the rod threads - still with enough "thread meat" to hold it there securely -- I think, I hope.
The test drive afterwards was a revelation. Boost rocketed up to 17 psi by about 2000 rpm in second gear. This, even though I have turned the main fueling screw back down, and show zero black smoke under load.
I have never seen boost build so fast in a turbo motor, not even a gasoline motor. Accelleration was a night and day improvement, in every gear. Nirvana.
So, the moral of the story, for anyone trying to make adequate boost on their stock K14, is to get the locknuts to the EXTREME end of the threads on the wastegate actuator rod. Put them even farther than the photo shows in the Smog FAQ (which is already pretty far!).
It is only the last 1/4" or less of those threads that make a blind bit of difference, even though the threads run for about 3" in from the end of the rod.
I can't understand what KKK was thinking in running the threads so far inwards from the end of that rod. Maybe there are applications where you would want only 1 or 2 psi max boost from the K14, which is probably what you'd get if you moved the locknuts even one inch in from the end of the rod.
-
#1
by
X@V
on 23 Nov, 2005 15:30
-
On my K14, I made a boost bleed. The boost peaks to 20 and stays to 17 PSI.
It's enough for my set-up.
-
#2
by
QuickTD
on 23 Nov, 2005 15:33
-
If you're adjusting locknuts you must be talking about a K03 with a remote wastegate actuator and not a K14. The K14 has its wastegate actuator mounted directly on the turbine housing and provides very limited adjustment.
I have a feeling that you're problem isn't with the actuator adjustment at all. What you have done by adjusting the actuator to the extreme end of the rod is bottomed the actuator and limited the travel of the wastegate or prevented the wastegate from opening at all. To test my theory, remove the small vacuum hose from the wastegate actuator (not the bigger hose that is hooked to the compressor housing) and back off your adjustment some. I have a feeling it will work even better.
The AAZ engines used in golf/jetta have a partial EGR system, the only thing missing is the EGR valve itself. When working properly the system applies vacuum to the EGR valve (when present) and to the back side of the wastegate diaphram the to pull the wastegate open at light throttle, when the EGR system is operating. If the switch on the top of the pump, the solenoid valve or its associated wring is defective the wastegate will be pulled open at all times, severely limiting the boost. It is still possible, as you found, to get 12 psi or so but it will require near redline RPM's and full load. Pulling the vacuum line off of the backside of the actuator and plugging it will effectively disable these remnants of the EGR system and restore full boost pressure.
-
#3
by
ricosuave
on 23 Nov, 2005 15:46
-
great info guys, keep it up
-
#4
by
Otis2
on 23 Nov, 2005 16:13
-
Quick TD, I thought I had a K03, but Dave thought my description was more a K14. Engine is from a '97 Golf. In any case, the setup looks identical to the turbo & actuator rod in Smog's FAQ.
I believe that I already had that EGR business removed on this engine, and the vaccuum port on my wastegate diaphram can was already plugged off. At least I THINK it was the vaccuum port. There were two hoses of equal diameter, leading to two separate ports on the can (presumably on opposite sides of the diaphram itself). One of these two hoses has been cut & plugged with a bolt & some silicone RTV, and the other leads to the compressor housing.
Reading your comments makes me wonder if a previous owner/mechanic accidentally switched the hoses to these ports. I suppose the pressure signal hose could right now be led from the turbo compressor to the EGR vaccuum port on the diaphram can. If the hose & plug were accidentally switched on the can ports, then what driving symptoms would you expect? Similar to what I report?
I'm now thinking that if the diaphram can ports were accidentally switched, then maybe that explains why my bleed efforts had zero effect. The compressor signal was not going to the right place anyway, so a bleed was irrelevant.
I will switch the plug & compressor hose around on the two ports on the diaphram can, then back down the lock nuts, test drive, and see what happens.
I agree that I have probably bottomed out the wastegate at present, since it is pretty much impossible to get less than 5 psi of boost in any gear, no matter how softly I try to drive.
-
#5
by
QuickTD
on 23 Nov, 2005 16:38
-
You have a K03 if it looks like smog's photo's and the car is a 97. Pre 95 cars had K14's or garret T2's on the passat.
The boost pressure hose should be connected to the base of the wastegate "can", the side where the actuator rod emerges. The other side should be left open to atmosphere. If the hoses were reversed the wastegate would close harder with increasing boost so you would higher than normal boost pressure.
another thought came to mind, is there any chance that someone has loosened and rotated the compressor housing? Since the compressor housing clamp holds the actuator, the relationship between the actuator and the wastegate linkage can be disturbed if the compressor housing is rotated. This might also be the reason that your rod adjustment is out of whack. If the wastegate still has some travel left you should be able to push the rod into the can with a fair bit of hand pressure, probably 20lbs or so of force. If you are able to move it 1/8" or so it should be OK.
The 5psi of boost at any speed is perfectly normal, mine does the same thing. Normal highway cruising boost at 100km/h is 7psi.
-
#6
by
935racer
on 23 Nov, 2005 17:20
-
Quicktd is right you have a ko3, I thought you said you had a k14 but it would be easy to confuse them as most people don't know that the ko3 was even offered due to the 1.9td only being offered in canada (no U.S. Model) glad you had some success in getting your boost up, added boost means more airflow which means you can add more fuel which means more power :twisted:
-
#7
by
Otis2
on 23 Nov, 2005 19:56
-
I think Quick TD is on the money with the rotation of the compressor housing idea.
The boost and (plugged) vaccuum hoses were already connected to the correct ports of the diaphram can, so no problem there.
The vaccuum side is not open to atmosphere, as it is plugged. I may leave it that way to keep dirt out of it. The plug doesn't seem to ever have restricted the wastegate from opening in the past. The problem was the reverse: the wastegate was opening too freely.
I don't have another AAZ to compare it to, but I can see how pointing the compressor's air outlet upward, and more vertically, would "stretch" the distance between the diaphram and the wastegate lever arm. So this may very well be the reason for my locknut issue.
I think the locknuts are rigged correctly now, relative to the rotation of the compressor housing. When I push the wastegate arm towards the diaphram can, I can definitely move it about 1/8" and hear it "click" deep inside. So if 1/8" is all the movement that lever arm needs, then the wastegate still has enough room to open & shut.
-
#8
by
Cheesetoast
on 24 Nov, 2005 18:31
-
my 93 1.9td can hit 25+ psi no prob, stock turbo, i have it running 20psi sustained, 21 peak. Greddy profec b spec II boost controller. at crusing speed with minimal throttle, i do 4-5psi. freeway cruising above 100kmph is 7psi -10psi