Hello I hope somebody could give me some knowledge on this ? underneath my 04 Jeep Grand Cherokee Laredo 4wd there are 3 gas lines on driver side going to rear and the brake line is on top going back to brake line block. My question is at the end of one of the gas lines which I thought was a gas line it stops and there should be a hose that connects to something else. It is a vacuum hose so I need to know where it is supposed to lead to. Hope somebody got the answer this is my first Jeep so I am a little lost..

 

Yeah, it's supposed to go to the vapor canister that's behind and above the rear wheel. On my 2000 4.0L it's under the hood, but with the 4.7L V8, there isn't enough room up there so they moved it to the back. They may have done this with the later model 4.0s as well. It's the canister purge line that sucks the captured fuel out of the canister every time you start it cold. The canister system is positioned in the worst place I can think of to keep it clean and rust free.

 

Thank you so much and sorry I didnt reply back until now. So does it connect to the small nipple piece that sucks out on the vapor canister? That's the smallest piece that because the other ports fat hoses go on. I guess whoever I bought vehicle off took pieces off and forgot to replace new hoses. I hope this will fix the problem with my vehicle feeling like it has hardly any power ATM.

 

Well, it is a vacuum leak that could be causing a lean mixture. Try just plugging that hose and see if it makes a difference. Fuel vapors from the tank are collected in the carbon canister and are removed from the carbon chamber by that hose and burnt in the engine. On cold startup, the purge solenoid closes and activates the purge pump to check vacuum integrity of the system. If the system won't hold a vacuum or bleeds down at less than a predetermined time, it will set an Evap code. It's been a while since I worked on one of these systems, but sometimes there is a filter in the bottom of the canister and it might be plugged with mud or something that will confuse the system into thinking it's working when it's not. GM systems in the late 70's were known for this.

 

It seems like you definitely know what you're talking about and I need the help the little things are the ones that drive me crazy but I love learning new skills. I'm actually going to take a couple pictures of the middle gas line with the hose that is connected to it and of the hoses that are connected to my canister already. I'll upload them asap. Thank you for all the info I appreciate it much.

 

The best move I made was downloading the Factory Service Manual for my specific year jeep. Every system is fully explained as to function, location of parts, and even circuit diagrams. When I got mine, it cost me around $10, but there are sites now where you can get it free. It's all pdf files that you can print and use on the job, then throw away when you're done if you like. The best part is the connector pinouts and wire color codes. The hardest part for this old fart was understanding the Can-Bus Data Link where all the modules talk to each other. Any time you find a twisted pair of wires, that's the data link.

I started cataloging all my printouts, but it's faster just to reprint new ones every time I need something rather than search my printed copies. Electrical diagrams can get hard to understand until you get the hang of what their symbolisms mean and where they get their power source. Different color highlighters make that job easier.

The one part that's lacking is any clue as to the internal circuitry of the PCM and modules, although you'd need a degree in computer science to follow that one anyhow! My advise is to not buy any jeep that's newer or plan on finding a good electrical diagnostic mechanic to work on it for you or buy a DRB scan tool and learn how to use it. That advise goes for ANY vehicle!