S4 Turbo II drivability help
06-02-14, 09:49 AM
#1
S4 Turbo II drivability help
I recently acquired another 87 turbo II, and I've been fixing all of the minor issues I've found, but I need some help.
Back story on the car:
I bought the car from the original owner. 111,xxx miles, 100% stock except for maintenance items (fuel pump, plugs/wires, etc). The car came with a folder full of an extensive maintenance history, and paperwork from Banzai Racing in Indianapolis. According to Banzai, the compression was an even 100psi on all six rotor faces the car starts, idles, and drives accordingly, so I do not doubt them.
Once I got the car home, I replaced all of the original vacuum lines that I could easily access, and replaced every rubber piece in the intake system (pre-turbo and after) with new silicon pieces.
The issues:
Currently, the idle is smooth and the car starts up fine, but there is a slight hesitation when you crack the throttle. I have adjusted the TPS, and that didn't help. I did, however, notice that the lean/rich adjustment on the passenger fender is set to full rich. If you turn that screw down at all, the idle gets erratic and it doesn't rev smoothly.
Also, the car doesn't seem to be making any boost. The factory boost gauge never goes above 0, and it takes it a while to get there (All of the electronics in the car are still fully functional, so I somewhat trust this gauge). I pulled the bypass valve out of the intake boot and plugged that hole to test. With that hole in the intake boot plugged, the car will not idle with the bypass valve venting to the atmosphere. It seems to be leaking vacuum, which in turn (I assume) would also leak boost. Does this sound like my bypass valve is faulty? Whenever I hold my thumb over the bypass valve to keep it running, and rev the engine in neutral, the turbo does not seem to build any pressure (when I do the same thing on my piston engine Mazdas, I at least get a little bit of pressure). Could the turbo not be spooling properly? I am able to spin the turbo with my finger, and there seems to be very minimal play, but I think I felt an occasional right spot while spinning it. That could just be my imagination.
I apologize for the lengthy post, and I appreciate any insight that can be given. Thanks in advance.
Jason
Back story on the car:
I bought the car from the original owner. 111,xxx miles, 100% stock except for maintenance items (fuel pump, plugs/wires, etc). The car came with a folder full of an extensive maintenance history, and paperwork from Banzai Racing in Indianapolis. According to Banzai, the compression was an even 100psi on all six rotor faces the car starts, idles, and drives accordingly, so I do not doubt them.
Once I got the car home, I replaced all of the original vacuum lines that I could easily access, and replaced every rubber piece in the intake system (pre-turbo and after) with new silicon pieces.
The issues:
Currently, the idle is smooth and the car starts up fine, but there is a slight hesitation when you crack the throttle. I have adjusted the TPS, and that didn't help. I did, however, notice that the lean/rich adjustment on the passenger fender is set to full rich. If you turn that screw down at all, the idle gets erratic and it doesn't rev smoothly.
Also, the car doesn't seem to be making any boost. The factory boost gauge never goes above 0, and it takes it a while to get there (All of the electronics in the car are still fully functional, so I somewhat trust this gauge). I pulled the bypass valve out of the intake boot and plugged that hole to test. With that hole in the intake boot plugged, the car will not idle with the bypass valve venting to the atmosphere. It seems to be leaking vacuum, which in turn (I assume) would also leak boost. Does this sound like my bypass valve is faulty? Whenever I hold my thumb over the bypass valve to keep it running, and rev the engine in neutral, the turbo does not seem to build any pressure (when I do the same thing on my piston engine Mazdas, I at least get a little bit of pressure). Could the turbo not be spooling properly? I am able to spin the turbo with my finger, and there seems to be very minimal play, but I think I felt an occasional right spot while spinning it. That could just be my imagination.
I apologize for the lengthy post, and I appreciate any insight that can be given. Thanks in advance.
Jason
06-04-14, 08:06 AM
#4
Bumping this up.
I'm still trying to figure out why the car hesitates, and why the lean/rich edjustment has to be at full rich for the car to run. Could there still be a vacuum leak that I haven't found? Maybe a clogged injector(s)? (Fuel pump and filter are new) Maybe base timing needs to be reset?
As for the car not building boost, I'm 98% sure the bypass valve is bad. I made a WTB thread in the classifieds for one.
I'm still trying to figure out why the car hesitates, and why the lean/rich edjustment has to be at full rich for the car to run. Could there still be a vacuum leak that I haven't found? Maybe a clogged injector(s)? (Fuel pump and filter are new) Maybe base timing needs to be reset?
As for the car not building boost, I'm 98% sure the bypass valve is bad. I made a WTB thread in the classifieds for one.
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08-07-14, 08:08 AM
#8
Just a quick update. It ended up being the timing. CAS was turned to fully retarded, which caused it to not build boost and stumble. Adjusted it via the FSM and she runs like new. I also did the fuel pump mod, which seemed to help some.
08-07-14, 08:46 AM
#9
Senior Member
Was going to suggest going and checking everything in the car from timing to spark. Anymore when I buy someone elses car I go through it and set it to what I know to be good, and replace maintenance items so I won't have a headache caused by things caused by the PO. I've learned the hard way on that one.
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