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skrlin

Gas mileage issue.....

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Long time member. Anyways, I have an 03 SS, had it from 24k miles, today it has 181,xxx just recently my MPG has gone down dramatically. Today just crusing around with light throttle MPG was showing a best of only 10-12 Mpg, again this is very light throttle, Also I have been getting a code P1516, I seem to be getting this when I engage cruise control. I use cruise control for my out of state business trips. Also I have a slight vibration around 60-70mph. Any help on this would be greatly appreciated. Truck has been maintained and serviced throughtout its mileage.

 

Thanks.

Edited by skrlin

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When's they last time you did a tune up? Can be a lot of things any loss of power? Is it sluggish?

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Long time member. Anyways, I have an 03 SS, had it from 24k miles, today it has 181,xxx just recently my MPG has gone down dramatically. Today just crusing around with light throttle MPG was showing a best of only 10-12 Mpg, again this is very light throttle, Also I have been getting a code P1516, I seem to be getting this when I engage cruise control. I use cruise control for my out of state business trips. Also I have a slight vibration around 60-70mph. Any help on this would be greatly appreciated. Truck has been maintained and serviced throughtout its mileage.

 

Thanks.

 

 

Vibration is most likely caused form Your tires being wither low or over pressure, needing them balanced or both, or feathering and cupping of the tire from not having them balanced and rotated every 5K....

 

That code is from the Throttle Actuator control within the throttle body. The TB can be going bad or it can be a bad or loose ground.

 

Not sure where your located but during winter months when the cold sets in, gas stations use a different mixture in the gas or a WINTER MIX and gas Mileage goes to hell until they switch it over. I would recommend looking at the plugs and wires and changing them if you havent in the last 30K. Get some Sea Foam and run that in the gas tank and the put some in the vacuum line at the brake booster to clean up and remove carbon deposits from upper engine... I would also replace your fuel filter. I bet with doing just this you will see an MPG increase.

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New Plugs and wires will help

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Did plugs and wires at 100k all with OEM parts. Truck has been sluggish. Noticed when trans is cold I do have hard shifts. I know I have a bad rim which I think is causing the vibration. Trans fluid from the stick looks good. Maybe i need to drop the pan and really look. could this be possible slippage in the trans?

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When I say light throttle I mean I am barely on it. IE like coasting and just to keep it rolling I am getting 10/12 MPG was never like this before

Edited by skrlin

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Did plugs and wires at 100k all with OEM parts. Truck has been sluggish. Noticed when trans is cold I do have hard shifts. I know I have a bad rim which I think is causing the vibration. Trans fluid from the stick looks good. Maybe i need to drop the pan and really look. could this be possible slippage in the trans?

is RPMs going up but truck still not accelerating?

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I have a good feeling that its has nothing to do with the components but the fact its sluggish and I have to give it more gas to keep up IE the mis match between the throttle. Will try the seafoam. I will check the grounds as well. Is there a specific one that causes problems? I know my in cab microphone/speaker for onstar rattles. Makes me believe possible ground issue. I know I tried to remove the fuel filter a while back and def had no luck. I know at the same time I cleaned out the throttle body as well.

Edited by skrlin

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is RPMs going up but truck still not accelerating?

 

Yes its like it goes up ever so slighlty and the gas is being dumped

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Are the oxygen sensors the originals? Is the check engine light on at all?

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No check engine light at all. O2s are orginal. Like I said only check engine light I get is when I set the cruise and then I get reduced engine power, which the scan shows P1516, this eventually clears out after like a couple restarts.

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You have 81K on the plugs and wires. I know GM says 100K to replace them, I think thats a bunch of BS. I always replace plugs around 30K and check the resistance of the wires as well. If they arent within spec I changed them. Every vehicle that I have replaced plugs on that had over 60K the plugs were junk, the gap was way off. Plugs and wires will help....

 

 

if you have a bent rim that will cause vibration..... The Onstar speaker making noise is a common problem and isnt from a grounding issue. The grounds I would check would b the ones on the back of the cylinder head, and the the one that mounts to the underside of your hood. Check for any corrosion on the actual braided wire itself. if it has corrosion replace it. the ground straps are only a few bucks each. Just make sure you get the right length as they sell varies lengths.

 

If you havent changed the filter and fluid on the tranny I would definitley do so. 181K is way over the service time for trans and filter. that should be done every 30K.

 

 

The truck getting that code of P1516 even after you cleaned the Throttle body, sounds like you need a new one.

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