Fuel Pressure gauge Flickers at 49 Vacuum @ 16

1999 Cherokee 4.0 Auto I have been trying to track down a loss of fuel mileage, and a slightly rough idle. I have replaced the coolant temp sensor, plugs wires cap and rotor, cleaned all grounds, replaced both 02 sensors. Yes I have the fuel pump that doesnt hold pressure, but still holds 49, while its running. I purchased a TPS, and it ran like crap, so I took it back and put the old one on. After replacing the 02 sensors I have been getting these codes; 132,135,141,138. I have checked all 02 wires, they are in good condition. My biggest problem and the only time I get the intermittent codes is when the 4.0 starts warms up for say 4-5 minutes it will suck the rpms and engine vacuum up and down up and down. I currently have a tank full of gas and lucas FI cleaner in it. When the problem begins to occur, my vacuum is reduced to like 10 and she starts sucking alot of air. I have cleaned the MAP port, The IAC and the manifold temp sensors. The vacuum slowly reducing to 10 made me think the cat is the problem, or a clogged muffler. The vacuum reads around 16 average on idle. Before I start replacing the big parts I thought I'd see if yall could help with this tricky lil problem. OOO 1 other thing when I replaced the TPS I went for a drive and the darn thing quit shifting, had to drive home in first gear! Any help would be great. Thanks

ok I took the gas cap off while it had been at idle for 30 minutes. got codes 135, 141,138 I code shorter this time lol, vacuum is reading a solid 17 and the fuel pressure gage quit flickering when the engine light came on? what ya think?

lol ok forget the gas cap. Um I have to agree with the guy that said why cant everyone just except that 4.0's are meant to have a 195 thermostat. It is my belief that not having a short heat up period is causing my fault codes in the heaters in my new 02 sensors. So that being said, I have purchased a new oem thermostat, a new cat because i prolly wore it down real good running rich , and a TPS which I didnt get a code for but my major stumble is in the same throttle area, and I had previous jeep with the same problem TPS so as it stands, it took me awhile of studying here at the forums, but I believe when i put these new parts on it will work lol anytakers on a bet?

Well thanx to everyone you has posted here, and slapped me with the obvious love the search threads. hope I dont have to respond and this doesnt work, caz nobody even tried to give an answer, but thanx anyway

If you put the cap back on will it return to the flickering and low vacuum? Seems like that shows a problem with the gas tank venting (charcoal canister?) or weak fuel pump. Have you done a fuel pump capacity test? But you also have a problem with the o2 sensor codes?????? You say you checked the wires, but have you checked for the correct voltage and ground? Did you check the TPS with an analog voltmeter looking for a needle jump showing a bad spot?

XJnBama said:

Well thanx to everyone you has posted here, and slapped me with the obvious love the search threads. hope I dont have to respond and this doesnt work, caz nobody even tried to give an answer, but thanx anyway

Click to expand...

Attitude?

Please allow me to beg your forbearance for all of the forum members and users that have jobs and families and other commitments and couldn't be available to meet your needs in a more timely manner.