GMC Jimmy Error Code 440

On a 1996 GMC Jimmy. For the past 3 months, I regularly (once every 2 weeks?) get a engine warning light resulting in code 440.
Initially, I was advised maybe it's just a bad batch of fuel or
tightness of fuel cap. Obviously after so many repeats, this is not the problem.
So I don't get hosed going to a mechanic right off the bat, what would be the causes of this issue and the methods of diagnoses and possible repairs or replacements required?
I don't notice any coincidingissues with the vehicle and fuel economy has not dropped since the start of the problem (although in the past month, since weather is colder, fuel economy has dropped noticeably!) Thank you.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is a leak in the evap system, after the fuel cap, then it becomes more difficult to diagnose, a smoke machine is the most common method of tracking this, otherwise lots of guesswork and parts may be on the horizon.

-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Shep wrote:

Yep it can be really fun to find the leak without a smoker. There are a few places you could look before you take it to a shop though IF you want to DIY.
The tank vent solenoid could be stuck open. Drop the spare and look for a black plastic line going to the valve. Disconnect the line and the wires and bend the retainer tab to get it off the mount.
The other end of the system is connected to the purge valve solenoid mounted on the intake manifold toward the back. One bolt on either side and it will pull out of the manifold. With it disconnected it should be closed, you can test it with a hand vacuum pump (or you can even blow through it). It shouldn't pass air to the intake side from the external fitting.
NO HIGH PRESSURE AIR on either valve or any part of the EVAP system.
The Vent Solenoid is about 30 bucks. The tank purge valve solenoid is 23 bucks.
The catch is that failures run about 50/50 for those parts.
Then it could also be a cracked or rusted line off the tank or along the frame. That can be checked with a hand vacuum pump by blocking one end and applying vacuum to the other end.
--
Steve W.
Near Cooperstown, New York
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I've had success by adapting a bicycle pump to the vapor system. (Nothing fancy - I ripped a valve out of an old bicycle tube and stuffed it in the end of one of the vapor hoses!) Pumping with a leak produced a hissing sound I could hunt down. When the leak was fixed the tank held pressure as felt on the pump and confirmed when I removed the fuel cap.
Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I forgot to mention - easy does it!!! Fingertip pressure on the pump only. The pump is made to put out 100 psi or more, which can do spectacular damage to a fuel system. The hissing starts at under 1 psi, but you have to have a quiet location to make it work.
Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.