can an EVAP test cause hard fill ups?

[Mike]

I’ve got a 2006 Chevy Trailblazer…while trying to troubleshoot a problem…I may have created another one. Playing with my scantool…I accidentally commanded an EVAP system test…THEN I put in a bottle of Techron fuel system cleaner..bottle got stuck and I had to twist and really pull to get it past that anti siphon tab. Just after that, I tried to fill the truck up at the gas station, but the pump kept shutting off. the only way to get gas in was to trickle it in real slow. No codes set relating to the EVAP system at the moment.(I had the infamous P0455 up until last month but finally fixed it).
I do have an on again/off again P0171 that I am trying to solve, but I’ve had no problems putting gas in until now.
So…if the EVAP test I started is still in progress (I think it takes a few drive cycles)would that cause hard fillups? or could I have screwed something up when I got that bottle stuck?

Topic

[Austin]

I’de go back with the scan tool and see if you can stop the test, or start it over and complete it so you at least know the status of the evap system and go from there. As far as the 0171 GM is famous for intake gaskets leaking, how many miles are on it? Since you have a scanner, pull up your Bank 1 sensor 1 and Bank 2 sensor 1, o2 sensors on a graph, start spraying around the manifold and different vacuum lines with carb cleaner, and when your o2 start running rich then you’ve found your leak. Before you do all that, throw a simple fuel pressure gauge on it since GM was nice enough to give us easy access shcrader valves, and make sure fuel pressure isn’t a problem.

P.S. what scanner are you using?

[Mike]

scanner is an Actron 9180
As for the EVAP system…I didn’t mean to start the test…pushed ‘enter’when I meant to hit the back button… over the past year, I replaced the vent solenoid which fixed my original fill up problem, but left the 0455 code, then replaced the purge solenoid which finally made that code go away. The 0171 started setting regularly right after that.

On that 0171…so far, I have tightened my intake manifold bolts (Trailblazers are famous for them being found loose), cleaned the throttle body, replaced the AIR check valve. I checked vacuum and I have a steady needle at 20 in/hg. One thing I do notice is that I often have a hissing sound when I push the brake pedal, makes me think I have a bad booster even though my vacuum seems to test ok. now I think about it…it’s intermittent…like the code… but I disconnected the brake booster and still have 20 in/Hg on the vacuum gauge. I do need to get a fuel pressure gauge and check that. I’m still new to looking at scan data, but I see that my LT FTRM is around 14% at idle…11-12% going down the interstate.

[Austin]

I dont use LT and STFT that often to be honest. For me I normally watch my upstream o2’s. everyone does things differently.

I would do one of two things for the 0171. Again check the fuel pressure, but do the o2 sensor test i mentioned with some carb cleaner. IF you get nothing there and the fuel pressure is okay, I would probably do a smoke test next. These test need to be done when the engine is cold. That’s the most effective way to do it. Making sure you’re not leaking vacuum around the purge sol. and then spray everything else down.

Another thing, don’t ever ever just go and tighten manifold bolts. If you want to check them or snug them, then use a torque wrench and go to spec. Plastic intake manifolds don’t take much at all, maybe 5-8 ft lbs. to much and you’ll crack it.

As far as the evap. If you can run the test again, then run the test again. Make sure for whatever reason it’s not commanded open or close. Make sure it’s back to it’s original position and then we can go from there.

keep us posted.

[Mike]

thanks for the advice.
shot a quick run on the scan data…don’t know if this yields anything useful for the sensors.

[Mike]

got down to a quarter of a tank today, so I went to the gas station. two things:
1. no problems at all gassing the old girl up. maybe the EVAP test finally completed.
2. I plugged the scanner in on the way back to the office from the gas station. Just leaving the station, my LT FTRM was still around 12%. few miles later, it’s closer to 3-4%. back at the office and idling in the parking lot it was around 5%. First time I’ve seen single digits there in a week or two.

either the fuel system cleaner worked, or could it have something to do with having a full gas tank?
…or the GM gremlins at work again?

[EricTheCarGuy]

That was an interesting problem indeed. Sounds like you have it solved however. If you have difficulty filling up again, I’d look to the EVAP system. You might want to go back over your work to make sure everything is connected correctly just to be on the safe side.

Thanks for the updates and keep us posted if things change.

[Mike]

yes, this truck is possessed. No more EVAP codes.

todays’ report: LT FTRM’s are back up to the 12-14% range. Check engine light is NOT on, however I see my old friend P0171 when I plug in the scanner.
From checking on a few forums, recurrent 0171’s are apparently common with this platform…so I’m not alone.

The truck drives reasonably well…I’ve had it about 2 years now…always felt it was a little lacking in power but this is the only Trailblazer I’ve ever driven so I don’t know for sure.

[Author]

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