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Re: Engine cutting off unexpectedly
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Thu, 4 Nov 2004 08:16:05 Share Post by Email
In Reply to: Engine cutting off unexpectedly, Ryan [Profile/Gallery] , Thu, 4 Nov 2004 07:41:25
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The trouble is that there are a lot of places where the problem could lie. There is the possibility of an ignition problem, or with the fuel-cut-off-switch, a fuel problem.

The clicking thing on the radiator is the APC solenoid, that helps control boost. By unplugging it (It made noise, so I hit it with a hammer until it stopped), you're limited to base boost. Why the overpressure switch was removed, I don't know.

I would start under the dash. The overpressure switch will kill the fuel pump when it opens (high pressure). Normally, it's closed, and only high pressure will open it. It gets two wires and a thin vacuum line that also goes to the boost gauge. If the switch was removed, the mechanic HAD TO connect those wires together, or the fuel pump wouldn't run. Just as a guess, I'd make sure the wires are connected together well. If they have an intermittent contact, that would mirror your problems. The pressure switch can be seen if you push the driver's seat all the way back, and climb into the footwell. Look up under the dash, on the firewall, above the clutch. Of course, if the switch has been removed, you won't see it. I'm going to guess (again) that the switch was faulty, or more likely, the mechanic was faulty, and he left the switch in place, and just pulled the wires off and taped them together. If the connection is bad, well, that's the problem.

Only the overpressure switch can cut off fuel in your year. Otherwise, if the boost pressure goes up, it moves the wastegate actuator, which causes the turbo to limit boost. Very smooth and seamless. The overpressure switch is a 'last resort' safety switch which should only kick in if the pressure goes way into the red, and all of the other boost control mechanisms have failed. If the switch tripped at a lower pressure, that would cause the engine to drop out at low boost. But there really isn't any other reason for the engine to quit due to boost.

The other issue could be ignition, and boost isn't related. The distributor has a hall-effect sensor for timing, and there is an ignition amplifier on the driver's side fender well. Those amplifiers have been know to get flaky. A sign of that would be if you crank the engine and the tachometer stays dead. Normally, the tach should bounce a little when cranking. To further confuse things, if there is no signal that the engine is cranking, the fuel pump relay won't pull in, and the fuel pump won't run.

I'd check the overpressure switch connections first.

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