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Dash gauges jitter then settle, stubborn starting, occasional stalls

I’ve done a lot of Googling and been to a mechanic, but no definitive answer on this one yet.

I have a 2003 GMC Savana that runs great, once it’s started. It’s stubborn to start though in that when I turn the key to the on/run position, the dash gauges and warning lights freak out for 5-10 seconds before settling to normal levels. If I try to start it while the gauges are jittering, the engine cranks but does not start. If I wait until the gauges settle, it starts perfectly.

As well, the engine will occasionally/infrequently just cut out while driving without warning. If I slip it into neutral, turn the key to off, and then restart, it starts immediately.

Battery and starter motor were replaced a few weeks ago, but that did not help.

Given that the dash gauges freak out and settle, I’m 99% sure this is electrical. Maybe a weak ground connection? Possibly a bad ignition switch, though I struggle to see how that would lead to initial gauge craziness that would settle.

Any thoughts, folks?

The guages my guess are independant of the real issue. Have a lot of keys on your keychain? ignition switch my first thought. Try driving it with one key and see if it makes a difference.

Good thought, especially since GMC had a huge recall of ignition switches a while back!

In my case, I use only the single key, so no keychain. And I’ve tried jiggling the key in the ignition to see if that might trigger the stall, but it doesn’t.

As mentioned, I’m particularly puzzled by the fact that the gauges/dials freak out and then settle. Something seems to be charging up, but I’m not sure what. And I don’t know if the startup and stall problems are related, though I suspect so, since they both started at the same time.

Thanks for the suggestion though…

I’m thinking along Barky’s idea above, that the gauges are a red herring. GM gauges can often fail in such a way b/c they operate with an electrical motor gadget, a stepper motor or servo motor or some kind of electrical actuator anyway, and that part is a pretty common failure item that affects GM gauges.

My guess is that the fuel rail isn’t quite up to pressure when you first start the engine, so while it cranks ok, it won’t start. Then after several tries or you crank long enough the pump finally pressurizes the fuel rail and it starts. And that time it takes to pressurize the fuel rail is about the same time as it takes the gauges to settle. So the gauge jiggling – according to my theory — is just a coincidence. The real problem is the fuel rail is leaking down when the engine is stopped. Faulty tank check valve or leaky fuel injector.

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In some vehicles, a breakdown in communication between the instrument panel and ECM will cause the engine to run poorly or stall. I don’t know if yours is one of these vehicles.

I want to mention another possible cause of these symptoms, namely bad diodes in the alternator.
When diodes are going bad, but have not yet failed, the result is usually a “ripple” effect with the alternator’s output, rather than a steady voltage. That ripple effect can cause various devices–like gauges–to operate oddly and inconsistently. In fact, that could even be the explanation for the OP having to replace the battery recently.

Having your mechanic check the alternator’s output would be a good idea, IMHO.

An experienced mechanic with an oscilloscope can often read alternator output to determine if a bad diode is causing peculiar problems. A 4 channel lab scope seems as essential to a mechanic these days as an OBD-2 scanner.