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Re: Boost problems
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Posted by Bob Davis (more from Bob Davis) on Fri, 17 May 2002 09:52:16 Share Post by Email
In Reply to: Boost problems.....(long), Harry, Fri, 17 May 2002 05:04:06
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>> 2. Took the W vacuum line off the APC solenoid. I was getting plenty of boost that way, so turbo is ok.

It should be boosting uncontrollably upon acceleration at that point, hitting the fuel cut off at full throttle.

>> 3. Reconnected the W hose and unplugged the APC solenoid. Again plenty of boost.

This is strange, as removing the connector should achieve only base boost.
Is it possible you or someone else accidentally got the vacuum hoses on the APC solenoid swapped around?

>> 5. Checked bypass valve by blowing/sucking in the small vacuum pipe coming out the rear of the valve. No leaks there.

If the bypass valve is bad it will tend to stall upon rapid deceleration, but if it isn't leaking it is probably okay.

>> 7. Checked APC voltage, resistance and air flow while on and off. It is definately working, it is buzzing hapilly. Everything is normal.

Just because it is buzzing doesn't mean it is working freely up and down the cylinder. Since I've had trouble with APCS's on every 9K I've owned, I'd suspect it first. Try replacing it with a known good unit, but before shelling out $215 at your Saab dealer, check with other vendors or parts yards. I have a used solenoid on my Aero from an early '90's 9K that cost $40 and it works perfectly. All solenoids for 2.3L engines have the same part number, so should be interchangeable.

>> 8. Sprayed APC solenoid with suitable lubricant/cleaner. No effect.

This sometimes, not always, will free a stuck solenoid. I actually revived one once doing this, but a second would not be fazed.

>> 1. Knock sensor. Couldn't find the bloody thing! Found two connectors behind the engine, under the manifold and behind the starter motor as someno suggested. One had a single wire, the other more than 2. Is it one of those?

You should have two sensors to the rear of the block, the knock sensor and the oil-pressure sender. The OPS will have one wire going to it, but I'm not sure about the KS, as I never played with one on previous cars. This Aero doesn't have a sensor, per se, anyway.

>> I suppose I could try another DI casette and see if it does the trick.

If bad, the DI will cause missing and possibly stalling, and shouldn't affect boost.

>> I'll try to find another APC solenoid to check with. However, mine has passed all the tests. Could it still be bad?

I would check the vacuum hoses going to the solenoid first for proper routing, then swap with a known good unit. Let us know.

>> 2. I cannot understand why disconnecting the APC solenoid should give you base boost. How would the wastegate open in order to reduce the boost without the APC solenoid? It looks to me that the wild boost I'm getting without the solenoid connected is correct.

None of my cars ever performed this way. The ECU regulates the amount of vacuum doled out by the APCS, and vacuum is what gives the wastegate its signals to open or close. Without those signals and without a vacuum source it only works up to base boost.


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