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08 CTS


Tractor

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I have an 08 CTS with the 3.6DI engine. I've never owned anything like a mustang or camaro, etc so to me this is a fun car to drive. My question though is why am I noticing that after each fill up the car lacks power big time compared to when its on its last 2-3 gallons. I find it kinda hard to believe that 90-100lbs of fuel weight makes that much of a difference in an already heavy all stock car. I've tried searching a few times, but I only get the opposite result "runs bad when near empty = rust in tank". I'm more inclined to think its something very simple like a gas cap, plugged vent, etc.

 

anyway its an interesting exercise of thought and its been very consistent over the past months.

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When you say lacks power, do you mean it just doesn't feel as fast but still rev's through the range smoothly? or does it sputter and buck and generally act like there is a real problem? Does it happen right after a fillup or just any time the tank is full.

 

It's rarer, but I have heard of sediment in the tank being churned up by the fuel coming into the tank and partially blocking the pickup and filter. If you let the car sit it will usually go back down and the car runs normally again.

 

in racing the difference between a full tank and an empty tank can sometimes mean a full second of lap time or more, so there is some merit to the car being sluggish when full and light when empty. In really light cars like miatas it can even make a difference in traction and weight balance. In your heavy pig of an AWD Cadillac you shouldn't really notice but maybe you are more sensitive to this sort of thing than most?

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Those have had lots of purge valve issues, I could see something like that being an issue but it usually would set a DTC when those leak.

 

Also pretty sure those had recalls for the fuel tank sender, so that's something to look into.

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By lacking power I mean it goes from feeling like a 300hp heavy pig car to feeling like a 90's corolla. No codes and the problem remains through at least half the tank of gas and then by the time I'm at the remaining few gallons its back to fun again. I don't typically drive far enough to run it down fast, I just take 10 to 30 mile trips every day or so.

 

A possible connection. I had a misfire on #6 that had been coming up when its very rainy for a few days. I replaced the plugs and eventually swapped the coil with #2. I've gotten a blinking CEL a couple times since then, but I can't make it fully code out and haven't had my laptop around at the time to see what pre code is in play. I'm guessing the misfire could have been a dirty connection to the coil and I'm going to clean them with electrical contact cleaner when I get the chance.

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  • 4 weeks later...
I have an old reader that can pull the codes and get a little data on some basic things. I'm thinking its very related to moisture. It went away for a few weeks and came back when we had some serious rain here. Its not enough to trigger a code now, but you can feel the power difference very well. I'm not sure where to go except pull all the ignition related connections and clean and seal them.
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