First of all the past year my jeep has been surging and connot find out the problem. Changed every possible sensor under the sun, TPS, Air temp, Coolant temp, MAP, air intake, O2..etc even replaced the throttle body. Still surges. Only other thoughts were in the tank, fuel pump, fuel pressure regulator, and filter, however wanted second opinons because i bought the jeep with iron skid plates under it and have to disasemble the one over the tank to drop it. PLEASE PLEASE HELP!!!

P.S only surges after 2 mins of running and will continue to surge for about 5+ mins. Also will give a backfire POP, no bang, just a little pop if i keep my foot on the gas. And i am getting terrible gas milage. Tried fuel injection cleaner, StaBil and better fuel. still the same problem. And more recently i get a raddle sometimes when accelerating at a stop light or sign. I think it could be a seperate issue but who knows, im just lost and need help because i have no monney for a mechanic to do it.

 

Where your injectors really dirty with black stuff? How long has it been since you replace the wires/cap/rotor do you have an exhaust leak anywhere?

 

havnt pulled the injectors yet, doing that actually right now, and i also replaced cap, button, wires and plugs. what does it mean if the injectors are nasty?

 

Have you verified the fuel pressure at the fuel rail with a mechanical pressure gauge. This will at least narrow things a little and rule out a fuel pump problem. Don't just push the valve on the rail. All that will do is show that you have fuel in the rail but not if you have the correct pressure. for your 99 Jeep you should have 49psi if I am not mistaken.

 

injectors are clean, This was a ultility vehicle for a comunications service here and everything under the hood looks mint and up to date. Injectors looked bran new. Also just pulled the plugs out to check em out, any build up, and clean as a whistle.

 

Have you checked all of your vacuum lines?

 

One other thing that you didn't mention is if you checked it for any stored codes. You can take it to any chain parts store such as AutoZone and have them run it for codes. They will run it for free. Just because you CEL isn't on it still may have codes stored.

 

Sounds like you have a clogged catalytic converter. Tap on it with a wrench or hammer lightly and see if you hear rattling. If so then replace it, as the internals have fallen and are blocking exhaust flow.

 

Would a cracked exhaust manifold cause this?

 

Yeah the cat sounds like a suspect

 

Could be different things, but I would look for a vacuum leak. Checking the fuel pressure (as mentioned above) is also a good idea.

 

I would be really surprised if a cat would get that messed up.. I've seen some get really bad, never gave symptoms like that. It is worth a check though. I'm leaning towards a vacuum leak. The best a quickest way to find the leak is using carb cleaner or a propane torch. Get a fire extinguisher or hose near for this job (i've scene it go wrong). I'd go with the propane torch. Start the engine. Turn the gas to about 3/4 open (not the flame lol do not light it) run it down all the vacuum lines and wait for the engine idle to change drastically, see if you can narrow it down.

Here is a video I found to help understand the process.
Hope it helps..

dave

 

Thank you everyone. Im going to try all of the sugestions tonight when i get home from work, and will keep you all posted. Again thank you all!

 

this!!!! i had the same problem with the 95 zj i had and it needed a cat. i went through all the same steps you did and finally someone mentioned the cat and replacing it fixed all the problems.... my cat was actually getting red hot after about 10 minutes of running. the way i tested it before replacing it was i just took it off and started it up. it ran 20x better so i towed it to my friend's shop and had him weld on a new cat.