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Discussion Starter · #1 ·
ive officially replaced and gone through every bit of this friggin APC system and still stuck in base boost. today i got around to what i thought was the last piece of the puzzle.. the overboost switch under the dash (not fuel cut-off). ive gone through every vac line / sensor etc. before i replaced the overboost sensor , i disconected the hose from the APC system to the wastegate and verified that i get full boost (im tempted to leave the friggin thing off). the solenoid chatters when tapping the knock sensor , i swapped out the APC box with two other replacements to see if it was that... still nothing, APC fuse is fine. i checked and adjusted engine timing twice , replaced the dizzy and vac advance module , had the knee bolster off today and checked the brake switch and any othe wiring.. all seems ok. what the hell now!! and on top of it , now when i turn the car off , put it in reverse (with clutch in ) take out the key, the damned reverse light still stay on !! could i have dislogded something that causes this condition now?
 

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I rechecked your older posts just to make sure I had put in my suggestions. I have.

I feel your frustrations as I've had my share when upgrading from LPT to FPT.

Do consider troubleshooting from the APC connector end when the car is stationary. Check voltages and resistances at the pins - I've put a summary down in http://saab.freeforums.org/apc-installation-t879.html. If your APC cannot see the voltages and resistances from there, it's not going to work. The connector is easy to reach and can tell you a lot about connections to the (in)operative components. Don't forget to measure resistance to ground to ensure it's well grounded.
 

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I don't think they often fail, but have you tried swapping out the solenoid switch just to eliminate that? I know you said it chatters, but if you have one on the shelf...
 

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Check out pin 20 on the APC connector. This is where the brake signal comes in to disable boost. On the PCB this is 12v. If this pin is stuck at ground for some reason the boost will be controlled only by the wastegate setting. The APC is not disabled, just not allowing boost. Just an idea. Check it out.
 

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Discussion Starter · #5 ·
thanks.
does anybody now why my reverse lights would not be going out now when the key is removed? im trying to think if i disconnected anything by the clutch pedal when i was swapping out the overboost sensor , but i was carefull and dont think so. is there any particular conection down there that has direct control on that function? i always have the clutch in before removing the key , which then turns off the reverse lights.

one more thing.... right on the bracket where the overboost sensor is mounted to , there are 2 relays and a multi-wire connector. i found a white/green wire with melted insulation there. i traced it back as far as i could and made sure it was still intact. i had to seperate it in a couple of spots from being melted to other wires. i thought that may have been causing some problem. i re-wrapped the wire with tape and made sure the connections were still good. any ideas on that>
 

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Discussion Starter · #6 ·
reverse light update

just went to the garage and removed the key as usual and all is normal... oh well i will run with it
 

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Discussion Starter · #7 ·
I rechecked your older posts just to make sure I had put in my suggestions. I have.

I feel your frustrations as I've had my share when upgrading from LPT to FPT.

Do consider troubleshooting from the APC connector end when the car is stationary. Check voltages and resistances at the pins - I've put a summary down in http://saab.freeforums.org/apc-installation-t879.html. If your APC cannot see the voltages and resistances from there, it's not going to work. The connector is easy to reach and can tell you a lot about connections to the (in)operative components. Don't forget to measure resistance to ground to ensure it's well grounded.
i will try this next. im fairly limited with multimeter skiils , but will give it a good try. does the ignition have to be on when checking these functions? i dont want to assume....
 

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i will try this next. im fairly limited with multimeter skiils , but will give it a good try. does the ignition have to be on when checking these functions? i dont want to assume....
It's both. Connectivity and resistance measurements can be taken with the ignition off. Power and testing the APC is with the power on, but engine not running.

Do give it a go, as the APC system is essentially an electronic control system with sensors and actuators. The electrical readings will give useful clues as to what's happening.
 

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Discussion Starter · #9 ·
still have to do the multimeter trouble shooting , but just was thinking.. what is the alternative to the APC system? is there a safe way to bypass it and still keep boost in a safe level?.... just wondring;)
 

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still have to do the multimeter trouble shooting , but just was thinking.. what is the alternative to the APC system? is there a safe way to bypass it and still keep boost in a safe level?.... just wondring;)
Fit a knock LED. APC pin 19 goes to ground when knock detected.
 

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Discussion Starter · #11 ·
right now i get full boost when i disconnect the hose from the wastegate to the apc solenoid. would i have to do something with that in conjunction with a knock led?
 

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Discussion Starter · #13 ·
thanks. i havent messed around with modding systems much , but i just looked up a universal MBC on ebay. does this go inline with that hose to the apc solenoid? if i take the apc solenoid out of the picture all together, where do i connect all the hoses. also , is the knock light crucial? if im into the throttle and it flashes, that means back off?

thanks again
 

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With an MBC the solenoid is out of the picture altogether. The MBC should be set so you don't go too far into boost inadvertently. When you have a knock light and it flashes, the idea is you lift your foot to reduce boost to avoid engine damage. I would suggest that the MBC is set so you only get knock flashes occasionally, then you lift. The MBC goes in the hose from the turbo pressure side and connects to the wastegate diaphragm. All the APC is doing is providing the knock light.
 
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