Been chasing some performance issues on my car now that I have a boost gauge. The whole point of the tiny turbo is to spool up quick and give a fat mesa of a torque curve from 2000 rpm up to 5000 rpm. But the car was a slug off the line, and even once the revs were up it felt weak. Gauge confirmed boost was very slow to build and peaked at barely 3.5 psi whereas the claimed spec is 6 psi.
Took the heat shield off and checked the wastegate linkage - darn thing was WAY loose and the pivot point had formed an oval from wear. It never closed completely, letting exhaust just fly past the turbine! No wonder boost was low and really laggy. As expected from two decades in the northeast the adjustment nut had corroded into an unrecognizable lump. I needed to get creative using a hose clamp and some steel wire to get everything back to where it should be. The white stuff on the linkage is anti-seize, and the white stuff on the flange is exhaust cement since it does leak a bit there.
This brought back a great deal of throttle response, but peak boost only went up to maybe 4.5 psi. I've had all the tubing apart just recently, and there were no symptoms of a leak to atmosphere. A leak of that size would murder my fuel economy and allow enough pirate air to throw codes. It had to be an internal leak at the compressor bypass valve (recirculating blowoff valve). This would let boost leak back to the inlet of the turbo, robbing performance without the computer seeing that anything is wrong. There was also signs of oil seeping out in the area, which only could have come from the bypass valve, as the turbo oil supply and drain lines were completely dry.
Rebuild kits are cheap so I ordered one and took the old unit apart. Annoying to access but I think I found my problem. Holy boostleak, Batman:
You are not supposed to see light shine through cracks in the diaphragm...
All the oil slime is from the PCV system, which means I probably should inspect and clean that soon. I did clean the housing, intake tube, and PCV solenoid while I had them apart.
Got the new kit installed, which was even more troublesome than the disassembly as I had to fight the spring to get the bolts started while also keeping the diaphragm seated. Since the intake tube needed to come off to give me access to the bypass valve, I also inspected the compressor wheel and checked for play. Very slight vertical play, even less horizontal play, and zero discernible axial play. After 187k miles this turbo feels brand new! Little bit of wear on the compressor leading edges but otherwise looks good in there.
Got it all back together and all I can say is wow. I had no idea how much grunt was missing. Even a quick part throttle burst brings the boost up to 4 psi. The manifold comes up to atmospheric more often and the car just pulls with barely any throttle. Once I do some more testing I'll see if I can put up a side by side comparison of the graphs from my data logger before the repair, after the wastegate adjustment, and after the bypass replacement.
If you have an older turbo car, I urge you to check these items, as you could be down a lot of boost without even realizing it.
Took the heat shield off and checked the wastegate linkage - darn thing was WAY loose and the pivot point had formed an oval from wear. It never closed completely, letting exhaust just fly past the turbine! No wonder boost was low and really laggy. As expected from two decades in the northeast the adjustment nut had corroded into an unrecognizable lump. I needed to get creative using a hose clamp and some steel wire to get everything back to where it should be. The white stuff on the linkage is anti-seize, and the white stuff on the flange is exhaust cement since it does leak a bit there.
This brought back a great deal of throttle response, but peak boost only went up to maybe 4.5 psi. I've had all the tubing apart just recently, and there were no symptoms of a leak to atmosphere. A leak of that size would murder my fuel economy and allow enough pirate air to throw codes. It had to be an internal leak at the compressor bypass valve (recirculating blowoff valve). This would let boost leak back to the inlet of the turbo, robbing performance without the computer seeing that anything is wrong. There was also signs of oil seeping out in the area, which only could have come from the bypass valve, as the turbo oil supply and drain lines were completely dry.
Rebuild kits are cheap so I ordered one and took the old unit apart. Annoying to access but I think I found my problem. Holy boostleak, Batman:
You are not supposed to see light shine through cracks in the diaphragm...
All the oil slime is from the PCV system, which means I probably should inspect and clean that soon. I did clean the housing, intake tube, and PCV solenoid while I had them apart.
Got the new kit installed, which was even more troublesome than the disassembly as I had to fight the spring to get the bolts started while also keeping the diaphragm seated. Since the intake tube needed to come off to give me access to the bypass valve, I also inspected the compressor wheel and checked for play. Very slight vertical play, even less horizontal play, and zero discernible axial play. After 187k miles this turbo feels brand new! Little bit of wear on the compressor leading edges but otherwise looks good in there.
Got it all back together and all I can say is wow. I had no idea how much grunt was missing. Even a quick part throttle burst brings the boost up to 4 psi. The manifold comes up to atmospheric more often and the car just pulls with barely any throttle. Once I do some more testing I'll see if I can put up a side by side comparison of the graphs from my data logger before the repair, after the wastegate adjustment, and after the bypass replacement.
If you have an older turbo car, I urge you to check these items, as you could be down a lot of boost without even realizing it.