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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a 1990 Chevrolet Silverado 1/2 ton pick up I

Customer Question

I have a 1990 Chevrolet Silverado 1/2 ton pick up I inherited from my dad. I replaced wires, checked timing, new air cleaner, and just typical routine stuff. It only has 70K miles on it. Dad had it sense new, and just stopped using it several years back. Problem is, it runs like a singer sewing machine, but only gets 7 mpg. Looking at the tail pipe, it burns white with no black smut. I have replaced a couple of sensors, but nothing has changed the bad mileage. Before I jerk all of this throttle body stuff off to it and go back to carburation, have you any thoughts?..Thank you
JA: Which particular sensor are you asking about? And have any trouble codes been triggered?
Customer: I have a $400 code reader, and it picks up nothing. I get no dash lights. The sensor I picked to replace was an air gas sensor on the intake manifold near the water inlet.
JA: Are you fixing your Silverado yourself? What have you tried so far?
Customer: Yes, it me. I am no pro, but 67 and rebuilt lots of engines in my life time. Once I had a cam go flat on one lobe, but it gave itself away by a rough idle. I have replaced plugs, wires, air cleaners, and removed and cleaned inside the throttle body expecting gum, but there was none. Then there was that one sensor I replaced, think that was telling it the block was below temp. I replaced the water thermostat with a 195 I think? Can't remember, but it was what ever the factory called for.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I took it to a shop in town here and sked for help. Their reply was that all these older trucks get bad mileage, and just don't worry about it. Wrong answer.
Submitted: 8 months ago.
Category: Chevy
Expert:  Todd M replied 8 months ago.

Hello. My name is ***** ***** I will be attempting to help you. Have you tried cleaning the idle air control valve? How about having the fuel pressure regulator checked?