Boost fluctuates at high RPM

jdulle

Veteran Member
Joined
Feb 4, 2017
Location
Ithaca, NY
TDI
96 B4, 97 B4
I have a 96 B4 tdi and it drives pretty well, has full boost at lower rpm, but at higher rpm you can feel the car surging as if the boost is going higher and lower. I have replaced some of the vacuum lines, but have yet to do the blue one. Also still need to open up the ecu and do the line inside. I would also like to get underneath and make sure the wastegate is moving freely. The injection quantity is a bit low (1.4) which might also cause this? Anyone have any other ideas? Possibly a boost leak? The car runs perfectly besides this and a little idle bounce between 900 and 1000 at times, especially while car is rolling...usually settles into normal idle after 10 sec.
 

Abacus

That helpful B4 guy
Joined
Nov 10, 2007
Location
Relocated from Maine to Dewey, AZ
TDI
Only the B4V left
There is more to the issue you're having than just boost, which is a function of many other things. I would look to your fueling since a partially plugged fuel filter will cause similar symptoms, plugged air filter or other air restrictionm (like dirty intake manifold), intercooler hoses that could have a crack or bad clamp (I had one of these on a B4 once), or partially plugged exhaust. A VCDS log scan with the car having the issue will tell you a lot and help narrow it down. I've found all of the issues above and even an EGR that opened prematurely due to being worn out.
 

jdulle

Veteran Member
Joined
Feb 4, 2017
Location
Ithaca, NY
TDI
96 B4, 97 B4
The air and fuel filter is new. I looked into the intake manifold and it looks like it could use a cleaning. So that is on the list. Also like you said the cat may be clogged. I noticed one clamp on the intercooler is broken (the one you want to remove to drain the oil out). I am hoping I can get the clamp off, one of the tabs you grab onto to expand the clamp is broken off. I will try to drain out the oil from the other end of the hose. Its driveable as is, plenty of power, but I will start going through the things that could be causing it and fixing. thanks for your response.
 

Abacus

That helpful B4 guy
Joined
Nov 10, 2007
Location
Relocated from Maine to Dewey, AZ
TDI
Only the B4V left
Glad to help. Odds are good the cat isn't too clogged to cause this but I've seem a few that were. It'd be the last thing I addressed on the list. I'd start with the clamp and intake cleaning and go from there. These intakes can be easiest cleaned with a torch and air, but you have to be careful to protect the EGR. Finding someone with a VCDS would be very helpful too.

Good luck.
 
Top