SandMountainJeep Posted December 29, 2013 Share Posted December 29, 2013 91 4.0 auto 4x4 running very rich when started, exhaust smells like raw gas. idle is very bad. If started and then shut off after just a couple of minutes then try to restart must hold pedal to floor to get it to start. Runs fair to good after warm up. It has been a lot worse since cold weather arrived. 116,000 miles, cat removed years ago. Thanks in advance for any help! Link to comment Share on other sites More sharing options...
cruiser54 Posted December 29, 2013 Share Posted December 29, 2013 MAP sensor tube There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor, behind the valve cover, higher up on the firewall. It has one vacuum line as already mentioned, with a 3-wire plug in the bottom. CRUCIAL!! The MAP sensor will tell the ECU to dump fuel with little to no vacuum to the MAP. Any crack or blockage and it will be pig-rich. ( black smoke, fouled black plugs, must hold your foot to the floor to keep the engine running). You can pull the line off the MAP sensor and feel for vacuum with your finger. If it runs! A visual inspection usually reveals any issues with the line from the throttle body to the MAP sensor. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 29, 2013 Share Posted December 29, 2013 ^^ That. Only thing is that you have a 91 so the plastic vacuum tube originates on the intake manifold, not the throttle body. Make sure that tube is connected to the MAP sensor on the firewall and that it's not cracked. Also check that the 5VDC supply voltage is present on the VIO/WHT wire on the 3-pin MAP connector (pic below) when the IGN key is on or the MAP sensor will not work. Have you checked for fault codes? Use this procedure and count the flashing lights: http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/ Link to comment Share on other sites More sharing options...
SandMountainJeep Posted December 30, 2013 Author Share Posted December 30, 2013 Cruiser, seems the tube is partially blocked as very little air is getting through. Is it ok to replace it with a piece of vacuum hose? Does the hose need to be a certain diameter to regulate the amount of vacuum? Also Don I'll check the codes and voltage. The check engine light did come on when I removed the line. Thanks to you both! Link to comment Share on other sites More sharing options...
cruiser54 Posted December 30, 2013 Share Posted December 30, 2013 Cruiser, seems the tube is partially blocked as very little air is getting through. Is it ok to replace it with a piece of vacuum hose? Does the hose need to be a certain diameter to regulate the amount of vacuum? Also Don I'll check the codes and voltage. The check engine light did come on when I removed the line. Thanks to you both! Any vacuum line will work. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now