boost problem .. related to check valve etc.

 # Flow diagram : saab 9-5 M2006 ~

 

 

 

  # Flow diagram : saab 9-5  ~ M2005

 

 

 

 

 

Alright, so as you can see I've circled the check valves that fail. These one-way valves make it so that the vacuum from the throttlebody at lower power levels pulling air from the intake cobra. It also keeps pressurized air from the throttle body from escaping and going back before the turbo since the cobra is at negative pressure from the turbo sucking in air at a rapid rate at high power scenarios. Having the check valves set-up the way they are allows the EVAP system to purge when the engine is vacuuming or boosting.

Anyway, what happens is when the top check valve fails, it allows the charged air from the throttle body (when turbo is boosting) to flow the wrong way through the EVAP purge system's tubes. This pressure flows down through the lower check valve (doesn't matter whether it's good or bad) and runs into the intake cobra and to our boost control valve through that "T." That pressure then pushes open a switch inside the BCV that is meant to resist vacuum (or pressure from inside the BCV) and is controlled by the ECU. After that pressure runs into our BCV and out through the wastegate nipple (combining with another charged air vacuum line which is the bottom nipple) and causes the wastegate to open prematurely.

When the wastegate opens, exhaust gasses bypass the hot-side turbine inside the turbo and in return, the turbo slows down. Because it is opened prematurely, the turbo never has a chance to create full boost, and the turbo gauge reflects that.

My guess is that the reason the top one-way valve fails is because it is under a lot of pressure under WOT, and then straight to vacuum when off the throttle. This is constantly happening even in normal driving conditions. The bottom one-way valve probably lasts much longer because it never sees nearly the same amount of pressure either way.

It is perfectly okay to run the car without replacing that top check valve as the purge system will still operate correctly with one correctly operating valve. However, there is probably minimal performance loss as the pressure inside the throttle body will always be bleeding back into the intake cobra. However, on a stock tune the turbo will be able to compensate for the minor loss. People with aftermarket tunes may like to replace the valves because as we all know, any little bit of boost helps in the higher RPMs when the TD-04 can't hold 21 psi.

If there are any inaccuracies, please post. Hope this helps you guys understand what's going on with this "fix."

 

 

 

 

 

 

 # Bolt mod : check valve 문제시 대안으로 사용 -  트로틀 쪽 체크밸브 문제로 인한 부스트 빠짐방지

 

 

 

 

 

 

 

 

 

 

 

 

Turbo Boost Adjustment (APC Cars)

 

STEP 1 First make sure there are no leaks that open under boost. You could be getting boost, but the leak opens up under pressure and vents it to the atmosphere. Pay attention to the intake tubes and the metal tube between the turbo and the intercooler where it passes under the over heat switch for the compressor in the top radiator hose. If the clamps here rub the tube, they will eventually wear a hole that will behave like this for a while.

 

STEP 2 Second, listen for a click from the solenoid valve when the key is turned on. The APC should send power to the solenoid and it has a permanent ground, so with the key on, one audible click should come from it. If not, check the fuses and then the wiring to the APC solenoid. one wire should have 12V with the key on and the other ground. Check each one for shorting to ground or power. It is common for them to lose their insulation and keep the solenoid from energizing. If the solenoid clicks, verify that it is actually opening its passageways, remove the hoses coming from it. You should be able to blow through the hose going to the center nipple on the solenoid ( marked C for Charge) and feel the air come out the left nipple( marked R for Return) With the solenoid closed ( key off or solenoid unplugged), this passage should be closed, no air between C and R. But you should have air flowing between C and W (Waste gate, right nipple) Check the routing of the hoses, R goes to the nipple on the intake tube, C goes to the nipple on the turbo's compressor, W goes to the waste gate actuator, below the turbo.

 

STEP 3 If all that is working and connected correctly. you can quickly rule out the knock detector by unbolting it, leaving it connected to its wiring, wrapping it in a rag, and securing it for a test drive. Do this just for the test, leaving it this way will eliminate any knock detection. If you now get boost, the knock detector or its wiring is bad. Inspect the detector for cracks in its housing. There was an update for early detectors requiring a new detector and hold down bolt, and a bulletin about interference in early harnesses to the detector that were not shielded properly. A kit is available to repair the harness if needed. Make sure to route the harness as far from the starter/alternator wiring as possible, the amps in these wires can induce voltage in the knock detector harness.

 

STEP 4 Check the pressure transducer next. You will need a pressure gauge, an ohm meter and a Mity Vac. With the key on, disconnect the vacuum line going to the transducer at the manifold. Pump up .5 Bar pressure. The APC solenoid should chatter away. If the solenoid chatters, the APC control unit and the pressure transducer are working. To get deeper into the transducer, you will need to measure its resistance at various pressures. on 82 1/2 to 83s, disconnect the wiring to the transducer and measure directly off its terminals. on 83-85, measure the resistance at pins 8 and 9 of the APC control unit with the unit disconnected. on 86 up, measure between pins 10 and 23 of the APC unit with it unplugged. At atmosphere, the spec is 5-13 ohms. Then pump up a pressure of 1.0 Bar (15 psi) and let it off to .6 Bar (9 psi). The resistance should be 88 ohms +/- .5.

 

STEP 5 If you have cruise control, make sure the cruise boost limiting switch is correct. If you have a older manual and a blue capped vacuum switch on the left fender well (up shift light actuator), the red capped boost limiting switch can plug into it and you will only have base boost if the two connectors are swapped. The wiring for the up shift light vacuum switch is gray/white and white and is a smaller gauge wire than the yellow/white wires to the boost limit switch. With cruise on, the limit switch interrupts the power to the APC solenoid that is if the cruise vacuum lines have vacuum in them).

 

STEP 6 Make sure the APC box is not getting a brake light signal on 86 and up cars. If you apply the brakes, the APC dumps boost. Check pin 20 for voltage, if there is voltage here, the APC thinks the brakes are on.

 

STEP 7 Check the rpm signal into the APC unit. on 82 -85 it will come in on pin 7, a blue/red wire. on 86 up, it comes in on pin 25 a blue/red wire. 86s are special with their ignition amp relay, so a couple of more steps are needed on them if the signal is missing.

 

STEP 8 Check for power into the APC unit on pin 14 of the 82 (off fuse 16) and pin 14 till 86 off fuse 10. 86 and up comes in on pin 13 from fuse 10.

 

STEP 9 Check ground for the unit on pin 6 of 82-85 and pin 5 of 86 and up.

 

STEP 10 You can check the knock detector at the APC connector on 82-85 at pins 2 and 3 (pin 1 is the shield). Look for ac voltage when you tap on the block. It will be a small voltage, reason interference is so common on this signal. on 86 and up, check it on pins 16 and 17 with pin 4 being the shield.

 

STEP 11 If you go through all this and it still doesn't work, chances are the APC box is bad.

 

STEP 12 To check base boost, unplug the solenoid, attach a pressure gauge to a manifold vacuum source (one behind the throttle plate) and go drive hard up a hill in third gear. Note the highest pressure you see.

 

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So I think that my Boost Pressure Control valve is not working as it should. I'm getting the overboost fuelcut problem. My research is telling me that the best bet is to just clean it with compressed air. I read a post that said that if you replace it it will probably just need to be cleaned in a year or so anyway.Sounds like you are referring to one of my old posts, where I quoted a mechanic who cleaned my boost pressure control valve with compressed air. He used shop air, but suggested using a can of dry air from an office supply.

 

I would unplug it first and leave the hoses in place to see if the engine still overboosts. Details below.

 

Cleaning v. Replacement: Assuming the valve has not failed on your car, the reason for cleaning instead of replacing is simple. on an old car, just like the IAC, once they start getting full of crud a new one will clog up as fast as a cleaned one.

 

Symptoms: At first the boost just goes down a little bit at a time as the valve gets dirty and operates more slowly. You can hardly tell, most people are at full boost for a few seconds and don't care that much on an older car. I only noticed the difference until it started to stick, had it cleaned, and looked at the boost gauge... :cheesy:

 

Once the valve starts to stick open between the C and R ports, the engine will overboost, resulting in a fuel cut by the ecu... You definitely notice that when it starts happening. At first it may just be once in a while, then each time on hard accelleration as the engine reaches a higher rpm at wide open throttle.

 

Connections: The BPC valve has one two-wire electrical connection to the ecu and three pressure ports, one In (C) and two Out (W and R), each with a silicone rubber hose connected to the turbo, waste gate, and the turbo air inlet duct.

 

C - from turbo Compressor into the BPC valve

W - from BPC valve to Waste gate actuator

R - pressure Reduction port, back to the air intake

 

To control the boost in the range between base boost and the stock maximum, the the ecu uses the solenoid valve to bleed off some air from "W" (waste gate actuator) to "R" (back to the turbo inlet).

 

Diagnosing: A leak in one of the BPC hoses, a bad BPC solenoid, or a bad electrical connection can cause the same symptoms as a dirty BPC valve.

 

With no power applied, the BPC valve should be open from C to W, and closed from C to R.

 

If you disconnect the BPC solenoid or bypass the BPC valve ("C", compressor directly to "W" waste gate), you should get base boost (middle of the yellow on the turbo gauge), and no fuel cut.

 

If you get no fuel cut with BPC disconnected, it is the valve.

If you get fuel cuts with the solenoid disconnected, bypass it to make sure.

If you get fuel cuts with the BPC bypassed, there is another problem.

 

Cleaning: Try compressed air first. I would not use carb cleaner, because ot may not be safe for electrically operated valves. Plain old isopropyl alcohol for a couple bucks at a drug store should do it if a can of compressed air won't, just may take a little longer.

 

Good luck.

 

Edit: I should add that although most of this applies both the the NG900 and the 9-3 models, the BPC valve for the 9-3 costs around $50-60, about 1/4 of the cost of the same part on the NG900. At that price replacemant may make more sense than cleaning.