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Gregory F
Gregory F, ASE Certified Technician
Category: Chevy
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I have a 1992 Chevy Silverado, 350, 5-speed. My gas mileage

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I have a 1992 Chevy Silverado, 350, 5-speed. My gas mileage has really gotten worse over the past couple of years. I used to get 19-20 and now I get 15 at best. My tail pipes are really black. I know I'm running rich. Any suggestions? It's been a few years since I changed the plugs/wires. I run 87 octane gas. My check engine light comes on every day after about 15-20 miles. I changed the EGR valve last year as this was the code that was indicated. I cleaned the old one once a year and the check engine light would quit coming on. It still comes on now. Your thoughts?
Submitted: 7 years ago.
Category: Chevy
Expert:  Gregory F replied 7 years ago.

Hello, the first thing is to verify what code you have. It sounds very possible that you may have an o2 sensor that is lazy and is contributing to an overfueling condition. After you check for codes, I recommend using a scan tool if you have access to one to check o2 fluctuation, coolant temp input, manifold absolute pressure sensor, etc. any of those are major inputs for calculation of fuel needs. With a scan tool we can proceed into some diagnosis. also checking base ignition timing is easy if you have a timing light ( should be zero degrees with set timing connector unplugged ). incorrect timing will contribute to poor gas mileage. If this info was helpful, click the ACCEPT button so I will receive credit/payment for my answer. If more info is needed, please contact me. Thanks for using JA

Customer: replied 7 years ago.
I expected a little more advice in regard to helping me solve my problem. I realize that the best approach would be a detailed computer analysis but that is pretty pricy. I try to take care of my basic maintenance needs. I am the original owner and have put over 200,000 miles on this truck. Other ideas that what you suggested? The timing is good.
Expert:  Gregory F replied 7 years ago.

Since the code can be read without a scan tool, lets verify that by jumpering terminal A to B in the aldl connector and with key on see what code flashes, then go from there

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