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Discussion Starter · #1 ·
Have been having some ongoing issues with my '08 Envoy for a couple of months. Have done a bunch of maintenance which hasn't fixed the problem (but that really needed doing anyway). Have a new theory but just wanted to run it past some other TrailVoy folks to see if I might be on the right path. FWIW prior to these issues, running great, starts with a flick of the key no issues whatsoever.

First time I had an issue I'd filled up with fuel, little bit of a shudder at start and another little shudder a few blocks from the gas station followed by a P0300 code. After this everything was fine until the next time I filled up with fuel. This time it didn't start first flick of the key and had to give it a second go, once again threw a P0300 not too long thereafter. Later in the day it threw a P0171. Since then it'll throw a P0171 pretty much once a trip if I'm out driving around. Filled up with gas yesterday and it was a seriously hard start, cranked for about 20 seconds before it fired, and again the P0300 followed by a P0171 later in the trip.

Now, over the course of these months in the attempt to track down this issue I have... checked the air filter and all of its ducts and hoses, replaced the MAP and MAF sensors, cleaned the throttle body and put in a new set of spark plugs as well as run through a couple of containers of fuel system/injector cleaner. Troubleshooting would say to change the fuel filter as part of that process, but I found out we don't have a discreet one on the 2008 (who's stupid idea was that)... so much for that idea. Basically all of the things you can do in an hour or so with a limited set of tools. I know the first thing everyone will likely say is check the intake manifold, and I am borrowing a smoke machine from a buddy to do just that... has not been done yet though.

However with all of that said it struck me that the only time it has an absolute fit starting is just after I've filled the tank at the gas station, any other time between fillups it starts no problems as always. Likewise the only time it throws the P0300 is shortly after fillup. Would it make sense to any of you if I were thinking that there's some sediment at the bottom of the tank that's gettting stirred up when I fill up... and that's kind of overwhelming whatever sort of filter is integrated into the fuel pump for a short time resulting in the problem start (so some combo of bad pump and/or clogged internal filtration)? Anything else that could cause that hard start immediately after refuelling and at no other time??? Am trying to hunt down a fuel pressure guage to see if the day-to-day fuel pressure is lower than it should be, as that would also explain the random P0171s.

Any other thoughts or suggestions that anyone might have are appreciated!

FWIW, a little tough for me to do too much driving testing on it right now since it seems to also have decided to spring a small leak in a power steering hose and I hate to drive when it's being mildly incontinent dribbling PS fluid whenever you turn a corner. :) But that's another project (that I didn't need to do) entirely. LOL

Mike
 

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2004 chevy trailblazer_lt
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Do you fill up at the same gas station?
 

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OK. Know anyone else who buys gas there that have experienced the same problem? While I agree with flyboy2610 about it likely being related to a saturated emissions canister, I'm also trying to rule out you getting bad gas. I've had it (bad gas) happen to me a couple of times, so it does happen.
 

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Discussion Starter · #6 ·
Can't say as I know anyone else that fills there (but probably everybody at my office) it's a high-volume 12 pump station in the downtown core... I fill up only every 2 weeks or so, in that month and a half I'm sure they've filled their tanks as much as I've filled mine :) I do understand your reasoning though, and that's why the most recent fill-up was at a different station, just in case.

What I'm not understanding with regard to the comments about the emissions canister is why the hard start and the P0300 are only occurring immediately after the fill-up. If the canister is saturated would it not be saturated all of the time?
 

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OK, I think we can rule out the bad gas. I am sure you would have heard co-workers complain about it.

Regarding the EVAP system and a saturated charcoal canister, here is my take. The EVAP system is a funny beast. It needs to be able to "breathe" freely so to speak in order for it to operate properly. It also must be able to be sealed properly in order to operate in a slight vacuum.

I speculate that when you purchase gas, you often try and top it off after the first time the nozzle shuts off the flow of gasoline into the tank. You either do this in order to get to the next "round currency figure" (e.g. $21.00 as opposed to $20.89) or you do it out of habit. Well, I used to be that way too - until I had to replace the charcoal emissions canister on our 1999 Buick Century because the engine was running just a wee bit too rich.

Now after you fill up and replace the gas cap, you now have a closed fuel system and the saturated charcoal canister is not allowing the EVAP system to freely "breathe" and the result is hard starting, a P0300 that appears after the fill up and the occasional P0171.

Now, I might be all wet on this too, and if anyone has the real answer, please chime in and educate us!
 

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Discussion Starter · #8 ·
Now after you fill up and replace the gas cap, you now have a closed fuel system and the saturated charcoal canister is not allowing the EVAP system to freely "breathe" and the result is hard starting, a P0300 that appears after the fill up and the occasional P0171.
I suppose it's possible, though in my gut I'd have an easier time believing it if at any other time during that two week post-fillup period there was even the tiniest hint of a hard start except sitting at the gas station. I think what'll be most telling is the fuel pressure reading once I get my hands on a tester next week... if the pressure's normal I can likely cross the pump/filter off list, if it's low then that becomes a bigger target.
 

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Good to hear you are going to see what the fuel pressure is. That is a darn good diagnostic test. However, I would think if your pump was putting out low pressure, the engine would be difficult to start all the time, not just right after a fill up.

Good Luck!
 

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My Ascender had difficulty starting after refilling the gas tank. In my case, I replaced the EVAP purge valve solenoid and that fixed it. But it threw a code for the EVAP system, not for the engine running lean. If you want to try it, that solenoid is cheap, but it’s hard to reach.
 
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