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92 Cabriolet... Overheat cutoff values?

After driving at highway speeds for a while, after stopping, my cabriolet will sometimes not start for a while (especially now we are in warmer weather). Since it does eventually start again, my current diagnosis is that the digifant II unit is seeing the engine as overheating and not allowing it to start.

The temperature inputs to the digifant are, according to the Bentley manual, the coolant temperature sensor and the air intake temperature sensor.

There are graphs of temperature vs resistance in the Bentley manual but does anyone know what temperature or resistance the digifant unit sees as being overheated? I need this to diagnose as it is quite possible that one of the sensors is faulty as I have had this happen on occasion when the car has been sitting all day doing nothing on hot days. Also, once the temperature has returned to "not overheated" is there a timed wait before it will start again (Disconnecting the coolant sensor does not make the car start but it will start normally with it disconnected [have not tried the air intake sendor so far])

Thanks

Rich

Reply to
Richard Thomas
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Pretty sure the ground strap is OK. When I turn the ignition, the voltage drops to about 11 volts so I'm not sure if the starter is seeing voltage or not. Hmm. Just a thought, maybe I'll try disconnecting the thick power line that runs to the starter and see if I get a similar voltage drop. Theory being that it's either the solenoid or the starter that is causing the 1V drop. If it's the starter and the engine isn't turning, then it's a problem with the starter. Then I'll see if I can disconnect the solenoid. If I still get the voltage drop then it's something else.

The thing that leads me to think it's the sensor is that it will start again if allowed to sit for a while. However. that voltage drop would seem suspicious if it was the digifant that was causing the engine to not start. i'm going to wire some diagnostic LEDs in this weekend I think.

I'll definitely take a look at that ground strap though. And i'l probably trim and reseat the starter cable too.

Rich

Reply to
Richard Thomas

Definitely not the ground strap, I tried bridging with jumper cables and still no go.

Interestingly, it did this again yesterday after only 3 minutes of running idle. The exhaust manifold was even cool enough to touch. I am beginning to suspect the brushes except that yesterday, there was not even a clicking sound (where when it has done this before, there has been).

Verified that it starts (but doesn't run well) with the coolant level sensor disconnected (as it should. As far as I can tell, this is no more than a user-indication) and the temperature sensor disconnected (though it didn't run well).

More diagnostics are in order. First step is to ID the solenoid wire and bung an LED indicator onto it.

Rich

Reply to
Richard Thomas

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