skroff

I am new to the form and the jeep world! I'm excited to learn how to work on my Cherokee. The jeep has a 4.0 straight six and is getting like 8 MPG! That is even up from the 5 MPG when I first got the jeep! I cleaned the air filter and found the connection between the censor map and the fuel throttle was broken. I have fixed that connection but there are still plenty of connections not hood up. The diagram in the books have been somewhat helpful but whoever build the jeep changed some things. There are some connections that I have no clue where they go and some parts I have no clue as well. The jeep is fuel injected but something is there might not be hooked up right. I know there are several factors fuel economy but I think the problem might be in the vacuum system or the injectors?? Here are some pics and some questions I have of what I am working with. I have some people say vacuum systems would not effect the MPG but I have had some say it could effect the MPG. Thanks for reading and for your help!

I cannot get the pics to upload, so I will attach them later.

VTJeep

i see no pics, just to be clear...
to the issues: an easy test for a vac leak is while driving, put the air on the foot setting and then give it gas and see if the airflow changes to the defrost vents. if it does, then ya got a leak somewhere.. as far as your gas mileage, that sucks dude! i got down to 11mpg at one point because my bank 2 o2 sensor went. here is a list to start getting familiar with if you want a better running jeep and have a few bucks to throw at it:
-good battery,terminals and wires, this includes solid grounds
-clean TB
-good TPS and IAC valve, also a CPS if your like pre '94
-02 sensors
-fuel pump/filters
-injectors (dodge neon injectors are a 4-hole design that give better throttle response)

things you can do besides replace random parts:
-put it on a code reader and see what it says, even if the CEL isnt on, there might be a code stored in there that will shed some light on your issues.
-sea foam, sea foam, sea foam... into your gas, oil, or right into your TB (while vehicle is running)
-make sure all fluids are good- engine and tranny being top priority.

these are basically all the things ive done to improve my jeeps gas milage. i sit right around 18mpg now.
good luck!

skroff

18 mpg would be fantastic. Most people I talk with about this say that is about what I should be getting. The pics I took were not uploading so I will try to attach them later today. I have recently changed the head gasket, valve cover gasket, oil pan gasket, and thermostat. The wife already asked me if I am going to pick up another job to pay for the jeep lol. I really want to get this nailed down so I can enjoy this rig. Thanks for the response. Could the vacuum system effect the MPG that bad? How do you know if the o2 sensors are bad? is there a way to check?

NorCalJeep

bump

Gee oh Dee

Moved to OEM Tech.

skroff

Have you tired to fix your MPG? From what I have read these Jeeps should be getting around 15-18 MPG! The vacuum system in my Jeep is all messed up. I need to get in and replace all the tubes. Hope that works. I'll try to post some pics.

JeepPockets

my jeeps smokes quite a bit and stalls and has hesitation, pretty sure its a 02 sensor for me... but it has also destroyed the MPG lol, not driving it in its current condition ofc

CPTslackass

With it smoking and hesitating, I'd check your MAP sensor.

skroff

Here are some pics of what I am dealing with. I checked the plugs yesterday and they look like they are running too hot. I need some help putting the vacuum system back together.

Mmurdock

If you do a search on this forum for "vacuum" you will find several threads with diagrams of the vacuum system (below is one I copied for reference). Figure out what's broke then hit the local wrecking yards to see what you can scrounge up cheap.

Some of the lines can be patched with regular rubber vacuum hose from the auto parts store. Just take a sample of the hard line with you to make sure the hose you get fits tight.

If you've got cash to spend you can buy a complete vacuum line system on the internet for around $80.

Good luck!

cruiser54

With the engine running spray some throttle body cleaner around the intake system. You'll know when you hit a vacuum leak. Be sure the hose to the MAP sensor is plugged into the correct hole on the throttle body.