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Re: APC ... now went BACK to 1/2 yellow (faulty APC?)
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Posted by Eric Law [Email] (more from Eric Law) on Wed, 20 Feb 2002 10:14:11 Share Post by Email
In Reply to: APC ... now went BACK to 1/2 yellow (faulty APC?), Taylor, Tue, 19 Feb 2002 18:38:11
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Taylor,
It sounds like you're waiting for someone on the forum to say "oh yeah its this", and you fix "this" and the problem disappears.

Sorry to say, but it's usually not like that with APC. APC is a great system, but it's got a lot of failure points, and they only good answer is you gotta go thru all of them until you find what's wrong - sometimes there are multiple problems.

Here are some things to check:
1) Faults inside the APC box - the box is in a location that gets wet in bad weather, and the seals on the box tend to harden and crack letting water in. Look for any corrosion on the PC boards. Also look very carefully for bad solder joints, especially where the connector attaches to the main board.

1a) The connector on the APC box and the mating one in the wiring harness - water can get in and corrode the terminals, sometimes they can also get loose. On the harness side, look at the terminals to make sure they're all positioned correctly and not bent.

2) Brake light switch - if the APC thinks the brakes are on, boost will be limited. When the boost is running low, try pulling up on the brake pedal with your toe - if boost increases, the switch needs adjusting or replacing.

3) Cruise control - there's a pressure-sensing switch that detects when the cruise is on, and limits the boost. Switch could be bad.

4) Power and ground - anything that interrupts power to the system will cause the boost to be limited.

5) The APC valve. With the ignition on but the engine not running, gently wiggle the connector to the valve. If you hear the valve "click", you've probably got a bad connection inside the valve and it will need to be replaced.

6) One that can be tricky to troubleshoot is the APC pressure sensor under the dash on the left-hand side. This is *not* the overboost fuel-cutoff switch, it's a separate sensor for the APC. Inside, this sensor is built a little like a fuel-level sensor - a contact slides along a coil of resistance wire. As the sensor ages, sometimes the contact will get a bad connection, which fools the APC box into thinking the boost is higher than it actually is. I've had some luck diagnosing this by doing the following: floor the car (preferably in a higher gear), observe low boost. *Quickly* lift your right foot then floor it again. If the boost level is significantly different each time you accelerate, you may have a pressure sensor problem.

Good luck!

Eric Law

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