I know I am about 2 cylinders and a few cubic inches short for asking a tech question in here, but I am stumped about my wife's trailblazer.


The vehicle at idle, would begin to lose rpm and act like it was going to stall. Finallly, after acting like this for awhile it did stall, and the SES light triggered. We had it scanned to find PO440 code came up ( loose gas cap).


How does a loose gas cap affect vehicle performance at idle? Is there a vaccuum being pulled on the tank? Does a lack of vacuum affect the fuel pump?

Well, the short answer is yes. Ever take the cap off and hear air rush in? That's a vaccum. Most GM cars have the fuel pump in the tank. That's right, electric pump in the tank. Lack of air in there keeps it from going BOOM among other things as you've found out. http://www.dieselplace.com/forum/smileys/Big Smile.gif Welcome to the world of emmissions controls. You'd be amazed what can trigger the SES light and cause performance loss.

If you'd tightened the cap and/or verified it's got a good seal and it's working again at idle, you've already answered your own question. http://www.dieselplace.com/forum/smileys/HiHi.gif

the stall is after it sits and idles for a period of time? If so, its stalling from an emmisions related problem. The fuel tank purge releases the fumes to fast and it basically kills the engine when its idleing. The purge will only effect it at idle and you likely will only noticeit after its been idling for a bit. If you take it off idle, the engine can push the purged fumes through and have no problems. There is a reprogram to correct the concern, have seen a few of them, one of them was before the reflash.... I have less hair after that

Thanks guys for the input


The stalling happens as soon as the car is started. It also was losing rpm in traffic at idle, but never stalled. It would seem to get better as it was driven.


Since we have "tightened" the gas cap, it has not been happening. Should we invest in a new cap? Do the threads on the cap wear out, and lose its "self locking" ability?

Just snug it up better after you fuel it up.

Eric,


Since the topic is already started about the I6 I've got another question. Does this thing have a PCV valve?


The reason I'm asking is that I like to run some injector cleaner straight every so often to clean the throttle body and innards. I normally get a can of sea foam and feed it through the pcv hose to feed the system 'evenly'. Problem is on the wifes car, I cant find it.


Rick