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Old 08-21-2007, 01:43 AM   #1
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Default Test light, ignition switch solve intermittent L27 stalling

I bought a '94 Olds Silhouette last month. It has the L27 3800 engine, so I figured I would be in familiar territory if it ever needed repairs. I did not have to wait long. Within a couple of weeks, the car stalled while driving. No chimes, no codes set, restarted normally. Then last week, driving down the road - car stalls as before, but this time, it will not restart. A quick check showed no spark at any of the coils. Towed it home.

Following the diagnostic procedure in the Factory Service Manual for the '92 Bonneville L27 (Chart A-3 "Cranks but will not run") led me to "ignition feed circuit open." In the Silhouette, it is pretty easy to find the ignition feed as it contains a 20-amp inline fuse at the front of the engine compartment. Placing the probe of my digital volt meter on the "hot" side of the ignition feed fuse holder gave me the same voltage as the battery, but a test light at the #5 injector would not light. It did not seem to make sense unless I had a bad wire between the ignition feed and the injectors. I really did not want to tear into the engine wiring harness looking for an open wire or bad connection.

I wasted a lot of time troubleshooting the ICM, Crank sensor, Cam sensor, related wiring, coils, and connectors trying to understand the problem when it occurred to me to try a test light at the ignition feed where I had consistently measured battery voltage.

When I tried the test light at the ignition feed in-line fuse, the test light would not light. 12.25V on the meter, but no light. Now, I'm sure that the more electrically astute will be quick to point out that the presence of voltage does not necessarily prove that a circuit is capable of carrying (much) current. And that is exactly what happened in this case. The problem was as the diagnostic procedure indicated, except the circuit was not open "enough" to show any voltage drop.

A new ignition switch solved the intermittent stalling problem. I hope that this information helps someone with a similar problem. I was reminded that a voltage measurement is not the same as a load test.
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Old 08-21-2007, 01:51 AM   #2
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Amen to unreliable voltage tests. Voltmeters are useless without a load.
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Old 08-21-2007, 07:47 AM   #3
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Each tool has it'* purpose and a multimeter has volts and amps for a reason.

Good reminder
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Old 08-21-2007, 12:52 PM   #4
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Great post for a reminder Bill. Even for those who know better, it may not pop right into mind when doing tests.

If an ammeter is used, be sure it can handle the current. Most DMM have a maximum of 10 amps, and would not suggest using it in a 20 amp circuit.
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