Low boost stock 94ss

[Damon]

I installed a boost gauge a few months ago to see what kinda boost the car was making. Peak is 5psi at full throttle and most of the time at partial throttle it stays at 0. Any ideas where to start? I replaced some of the vacuum lines but that didn't help, car is dog ass slow 94 legacy all stock except aftermarket muffler. About 210000 miles on it. I did check the wastegate and it does open and close, I opened and closed it with a pair of channel locks.

[cj91legss]

CE Light?

[Damon]

No cel light. I guess I could plug up the test connectors just to make sure though.

[brweber352]

5psi is very close to wastegate presuure(6psi), your gauge maybe off a tad. Of course start off by reinspecting your boost gauge lines, and possible boost leaks.

When the ECU senses knock it will default to wastegate pressure, which is 6psi. You may want to reset the ECU, then drive carefully for about 50 miles without getting into boost. Then try a WOT run and see if boost has gone back up to stock psi(I can't remember if this is 8psi or 9psi). If boost goes back up to stock psi then I would suspect you got knock at some point. Possible that maybe a tank of bad gas caused this. You are running 91-93 octane, right?

If boost does not return after reseting the ECU I would maybe think the boost control solenoid might have took a dive. The solenoid should throw a CEL if it is bad, but it may not aswell.

With 210k miles you could also have a clogged converter. Ever replaced it,had it checked?
I'd go ahead and check that air filter to!

CHECK ALL THE VACUUM LINES FIRST. Alot of times it is something simple like this. Make sure you reset the ECU PROPERLY, follow the directions in the Library or pull the fuse for the ECU/TCU for atleast 30-60 minutes. Boost should return to at least 8psi after reseting the ECU. If it does return to stock psi then falls back down again later, suspect knock/detonation from something, maybe a bad knock sensor.

Brian

[Damon]

Well, I checked the lines and reset the ecu. I didn't drive easy for 50 miles but it's still stuck at 5psi. I always run 93 so I guess I'll swap out the bcs when I get home tomorrow. Maybe the turbo is just tired after all those miles

[vrg3]

If you're not getting a code 45 the boost control solenoid is probably salvageable because the coil is intact.

Assuming the solenoid is at fault, try cleaning it out. Disconnect all the vacuum tubing from the solenoid and remove it from the car but leave it electrically connected. Hook up the green connectors under the dash to put the ECU in test mode and turn the ignition on but don't start the engine. It'll start cycling all the solenoids on and off. Hopefully you feel the boost control solenoid clicking back and forth at least a little. Even if not, though, you can still try cleaning it. Spray fuel injection cleaner into one of the fittings and try to get it to run out of the other two. You can try turning it around and upside down and stuff to get this to happen. You ought to be able to clean out whatever's making the solenoid stick.

I don't think your turbo is tired, but you may have an intake leak, an intake restriction, or an exhaust restriction like Brian suggests.

[HappyFrog]

Also check the hose on the turbo outlet, it may have cracked from being baked all these years. Mine was in a horrible state when I replaced it (had been repaired with tape by some previous owner at one point ).

Does boost drop when you go into higher rpms or does it stay at 5psi?

[Damon]

Also check the hose on the turbo outlet, it may have cracked from being baked all these years. Mine was in a horrible state when I replaced it (had been repaired with tape by some previous owner at one point ).

Does boost drop when you go into higher rpms or does it stay at 5psi?

Boost is constant 5psi no matter what gear or what the rpms are. I'm going to replace the bcs this weekend. I have another one from a lower mileage car. Hopefully that will liven things up.

[HappyFrog]

Did it help replacing the bcs? Definitely sounds like sensor/ecu problems when boost is constant, I would expect boost acting weird if you had a leak.

[Damon]

Did it help replacing the bcs? Definitely sounds like sensor/ecu problems when boost is constant, I would expect boost acting weird if you had a leak.

I didn't replace it. I did take it off and check it. It wasn't blocked so I put it back on. No change. I'm going to try to switch it out this weekend. I'll post the results.

[Mattheww044]

Im experiencing similar problems, along with a few others. I pressure washed my engine bay, and after starting the car, I got a constant CEL, but the car ran fine. I am only hitting 6psi now, so I am going to check the codes again (i cleared the codes a few days ago) and replace the knock sensor again if it is cracked or the connections look back. I replaced it less than a year ago though so I don't see how it would be bad. Would water hitting the knock sensor somehow cause it to crack if it was hot and the cold water hit it?

[Legacy777]

Check the codes and report back on what you find out.

[Mattheww044]

Knock sensor appears to be fine and the code went away. Not sure why Im only running 6psi....
What were your results Damon?

[Damon]

Knock sensor appears to be fine and the code went away. Not sure why Im only running 6psi....
What were your results Damon?

No results yet. I forgot to swap it out this weekend. I guess I should probably take a peek at my knock sensor too since they are notorious for cracking. On a side note when I did take out the bcs it was fairly straight forward and only took 1/2hr.

[Mattheww044]

yea, i just replaced my bcs so I don't think thats it. And the code doesnt come up anymore so thats a good sign

[WoodsWagon]

I didn't replace it. I did take it off and check it. It wasn't blocked so I put it back on. No change. I'm going to try to switch it out this weekend. I'll post the results.

If it's not blocked, then it will let boost pressure go straight to the wastegate actuator, and then the boost will be regulated by the wastegate spring pressure. The point of the BCS is to block boost pressure from going to the wastegate actuator, so it doesn't open, and the turbo creates higher pressures than the wastegate spring would normally allow.

So, you need to check that the BCS does actually block when it's activated. If it won't block, then the pressure will go straight through and you will only be able to attain wastegate spring pressure, which happens to be right around 5.5psi.

[Damon]

I didn't replace it. I did take it off and check it. It wasn't blocked so I put it back on. No change. I'm going to try to switch it out this weekend. I'll post the results.

If it's not blocked, then it will let boost pressure go straight to the wastegate actuator, and then the boost will be regulated by the wastegate spring pressure. The point of the BCS is to block boost pressure from going to the wastegate actuator, so it doesn't open, and the turbo creates higher pressures than the wastegate spring would normally allow.

So, you need to check that the BCS does actually block when it's activated. If it won't block, then the pressure will go straight through and you will only be able to attain wastegate spring pressure, which happens to be right around 5.5psi.

I'm going to switch it out this weekend, I managed to get the other one off my parts car but I didn't have time to switch it out. We'll see if it helps. I did manage to get the car to 10psi intermittently Friday though. Don't know what was going on there. Oddly the car didn't seem to pull any stronger at 10 so maybe my gauge is toast.

[Damon]

I changed the bcs and still no real change. It has a little better response but it's still not what it should be.

[trac]

Any updates on this?

[Damon]

Turns out the car only likes certain brands of gas. Even at the 9psi it doesn't feel like it pulls any harder than it did @5.