Hi,
I've got a 2000 Blazer and I just replaced the fuel pump on it two weeks ago and had the thermostat replaced last week. The first time I put gas into it after the thermostat was replaced, the next time I started it up the Service Engine light popped up. I ran it back to the mechanic and he said that the reading was something to do with the oxygen sensors and reset it, saying that we just replaced the fuel pump it's nothing to worry about, let us know if this happens again.
This morning, I got some gas again (left the car running). I went into a store for about 5 mins, came back out and started it up and the Engine light popped on again!! WTF? I have to take it back in tomorrow, but does anyone have any idea what could be causing this? Is it related to the thermostat replacement or the fuel pump or neither?

EDIT ** I should also note that I do have the codes for what the problem appears to be P0171 and P0174. Both of those codes indicate fuel injector issues as well as oxygen sensor issues**

 

Until you know the codes, all we can do is guess.

I'll start by guessing that you need a new fuel cap!

Who's next until we get the codes?

 

both codes are saying you are running lean.try cleaning your MAF (Mass Air Flow) Sensor with some maf cleaner. Also look for vacuum leaks.

what brand pump was installed? these blazers are PICKY. they only like ac delcos or delphi

 

to be clear, they dont reflect injectors OR the O2 sensors. Why? Because problems with a couple injectors wont likely end up in lean without driveability or startup issues.
And the O2's just report. Trying to fix it by replacing O2's is like killing the messenger before you are sure he's lying. In this case you have BOTH messengers with the same message.
It is possible you have a pressure problem due to junk in the filter originating with the FP replace. But USUALLY that doesnt show up while at low speed or idle.


Like Chris said, most likely a vacuum leak or possibly the MAF.
Have the mech check the short term fuel trims against the LTFT's on each side.

 

Thanks for all the feedback. Turns out it was a hose that was disconnected. At least that is what the mechanic told me today. Seems to be ok, we'll see when I start her up tomorrow

 

And- I betcha its that emissions hose on the fore end of the gas tank. What a pain to keep that one hooked up!

 

Hey Easy, could you give me a little more detail on the hose that mentioned. I've been underneath the Blazer before but never noticed anything loose, but I'd like to double check the hose that you mentioned. Is it at the front of the fuel tank? Is it easy to see? etc. Thanks man.

 

OK. I have a 96 Jimmy and had the fuel pump replaced. Odd emissions codes happening for quite some time. Then had to replace a leaking fuel tank. The 96 is probably different than the 2000 but I don't know. Mine has a 2 inch diameter valve with a plastic tit which connects to the fuel evap system. that tit thing was cracked and then broke off last time. I tried to JB weld a tube to it to reconnect to the vacu line and reinstalled the tank. No, it's not easy to see. It is at the front end, on top, close to the frame. You have to drop the tank on a 96 to even see it.