Hi, I had the car on stands for two weeks rebuilding the steering rack, replacing control arms, tie rods and doing Koni strut replacement surgery. I also took the time to retension the belts. I drove very carefully over to the alignment shop where they pushed and pulled the suspension back into shape. Eager to test out the new front end, I took off to do some driving.

On the low speed surface streets everyting felt fine. When I got onto the highway, things were different. As I merged onto the freeway, I pushed the throttle all the way down and around 5K rpm and at what looks like full boost, the car began to jerk, almost as if the rev limiter was hit, but stronger. I backed off on the throttle and the car seemed fine. It can operated in the high rpms if I move it up there gradually, but the second I lead foot it and bring on the boost, the stumbling happens.

The forums have presented several different possibilities, but I thought I would pose the question again to see if anyone has a more definitive answer.

Thanks!

Gene

 

If the car drives normally when not under boost, then I suspect the overboost protection is kicking in when you go WOT. Do you have an aftermarket boost gauge? If so, what does it show when this happens?

 

I don't have an aftermarket guage. The "precision" stock guage is all the way to the right. Adding a new gauge is on my endless list of things to do.

 

Look on top of your waste gate you have probley pulled the hose off moving stuff around. Be shure to not get under boost till its fixed you can do engine damage.

 

Can you see the top of the wastegate from the engine compartment, or so I need to put the car back on the stands and get at it from below?

 

its easyer to get under the car its on the pasenger side where the header and cross over from the turbo meet.

 

Superjet - welcome back

 

THANKYOU. Glad to be back. Feels like ive been gone way to long.

 

Also, check TPS

 

I have completely replaced every vacuum hose in the system and it did not fix the stumbling problem. It did return my idle closer to factory specifications and it was nice to remove the brittle and broken connectors. I am curious as the whether or not this could be overboost protection. There is a cut-off, but others have decribed overboost protection as being a one shot deal. Once you hit it, you have to turn the car off and then on again to resume normal operation. When it happens to me, I can keep making it occur and continue to drive the car normally.

I will check the TPS now and work down the list of a million things it may be. Any other hints would be helpful.

Thanks!

 

TPS checks out fine. Not sure what to check next. Wastegate maybe?

 

Could be the fuel pressure regulator. My car had symptoms like yours last year, 5K RPM seemed to be the point that triggered it. Turned out the FPR was spiking about 3 times normal pressures. New FPR fixed it!

 

It does sound like overboost protection. Be sure to inspect all the hoses leading to & from both the cycling valve and the wastegate. Is the boost gauge always (continuously) pegged?

 

I already checked and replaced all the vacuum hoses including the one leading from the valve to the wastegate. I fixed a couple of leaks, but this had no effect on the stumbling problem. Boost gauge is acting normally. The gauge registers as boost increases. My next thoughts were bad cycling valve, bad wastegate and AFM.

 

Gene,

Per Renn 951's suggestion i've got a practically brand new stock config. Bosch fuel pressure regulator (less than 400 miles) that I put in my car before going with the GURU chip upgrade. You are welcome to install it in your car and at least rule that factor out. I am free this Saturday until about 1PM. Email me if you are interested.
-Ben