hey guys.
im in canada so forgive me
i have a 97 gmc jimmy 4 door 4.3 w engine automatic (2x4wd i barley use 4x4 if ever)

i get about 250-350KM to a full tank of regular (seem normal?? seems bad to me)

and there a large vacuum hose running from under my truck to beside my radiator with a plug in the end of it, its covered where it goes under the motor with a protective wire loom wrap. is this suppose to be connected to something?
im getting a p0440 code so i know the EVAP system has a fault and am trying to widdle down the culprits.. this is the frist time ive ever had a car that ive decided not to remove all the emissions components for fuel reasons so im not sure where to start.

 

HI I'm from Canada as well I have a 1997 Blazer LS 4 door 4x4 I also get only 280-330KM but thats per 3/4 of a tank I always fill up at 1/4 tank as not to risk burning out my fuel pump.

The large vacuum line is for your 4x4 vacuum actuator under the battery tray on the passenger side, I assume that is the side of the radiator you are talking about. The way the 4x4 system works is like this

1) The vacuum lines start at the motor (source) goes to the check valve
2) The check valve has 2 outs one to the vacuum reserve ( ball on hood) and the other goes to a T
3) After the T the lines go to the HVAC system and the vacuum switch on the transfer case
4) The vacuum switch has 3 vacuum connections on it a vent, the source from the motor and the third goes from the switch to the vacuum actuator under the battery tray
So if that vacuum line is not connected then your 4x4 will not work

As for the Evap system I'm in the same boat as you, I have no codes yet, but when I put my code reader on my truck it reads that my Blazer has not yet completed the Evap system check so the emitions part of my reader stays yellow instead of being green

I hope the information I've given you at least helps you out a bit good luck

 

I would say the hose is the vent line for the front diff. (a vacuum line would not dead end like that) the plastic cap is a filter to help keep dirt out, Make sure it stays up high to avoid pulling water into the diff.

 

I believe you might have a point Blue Jay I forgot about the front diff vent hose


But Scorpious said "its covered where it goes under the motor with a protective wire loom wrap"

The hose could have bin disconnected because of a problem and they pluged it so 4X4 might not work.

So Scorpious does your 4X4 work properly? If not pull your battery and tray and see if there is a line connected to the actuator.

Just from my experience my vacuum line going to the vacuum actuator under the battery tray had the protective wire loom wrap on it as well, When I first saw this I thought it was part of the wiring harness until I took a closer look.

I also believe that the diff vent hose is a thick hose with no covering on it, but I could be wrong, it's bin a while since i've bin under there and had a look

 

It was the tranny line..
Mileage is still garbage... Getting reasonably worse aswell 250-300km max before close to red on gauge
I have, installed cai, fuel filter, Tstat, plugs, wires, distributed, sea foam, injector cleaner.
I'm tempted to change the PCM see if there's a difference

Also the p0440 was corrected with a new gas cap
No effect in my mileage

 

So the p0440 is the only code?

Does your temp ga look like engine is getting up to temp? I'd start with checking the ECT to make sure it's right

 

I put a new ECT sensor in.
No change.
Also my gauge is reading way off (or I'm assuming so$ dosent get above 60 Celsius

 

Last fillip drove 200km then filled with 46 liters
Ouch