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Q: Speedometer jumps up/down and van backfires. 1998 GMC Savana

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The speedometer in my van jumps up and down. The radio volume drops to almost nothing when it goes to 40 and then to 100. Plus, the van started backfiring when the engine is slightly cold and I’m pulling out. I took it to a professional auto shop and they worked on the temperature gauge, but it did not make any improvement in the speedometer problem. They even replaced it and the same thing is happening. Then they installed a Cam sensor and it stopped backfiring until today. Now it is backfiring again. Hundreds of dollars in repairs and the only thing working is the temperature guage! What will fix my van’s speedometer and backfiring problems?

A: Hi there, thanks for writing in about your ...

Hi there, thanks for writing in about your 1998 GMC Savana 2500. The speedometer and radio may work together to adjust volume of the radio as the speed increases. The cluster or any of the affected modules may have a connector issue from fretting corrosion in the connectors. I would suggest disconnecting the battery and disconnecting the connectors to the engine control module, body control module, and the instrument cluster to look for corrosion and clean and apply dielectric lube to the pins and lightly seal and reinstall to make sure connections are secure. If you need further assistance, a certified technician from YourMechanic can come to your car's location to inspect the speedometer and let you know what should be repaired.

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