Topic: Jeep running issues

[Rio_Grande]

Hello everyone
I have a 97 tj with a 2.5
Only mod is a k&n filter on a homemade tube I am trying to find a way to get rid of.
I have had problems with this jeep for some time. It originally lacked power at high rpm. Then it got to the point it woul only run for about 10 minutes then it would start to backfire and choke down to an idle. Pushing on the gas would lead to more backfiring and spitting. No codes.



I did a complete tune up, even wires, no help, changed the cps and temp sensor, no change. New fuel pump.  I had a big x crack in my exhaust manifold so I tore it down and had an accident the next day that left it torn down for almost two years. I had the valves redone, put it back together with new injector seals, plugs, and radiator. When I started it, the problem was gone, but as it  was run a bit it started doing it again but now it is at start up and within 3 min or so of running it straightens up and runs fine. Almost exactly opposite of before the tear down.

The fuel pump was new and it changed nothing, I was thinking converter but after the manifold repair it acts opposite of a converter?

What do you think? I see alot of this on the Internet but few ever say what it was.

[sharpxmen]

you have a TBI so i'm not that familiar with the computer on those, however i would start by checking the fuel pressure. If you replaced the pump you should also replace the filter if you didn't. Could be as simple as a bad injector (you only have 1) or some bad ground or connection, can also be as complicated as an ECU problem. My suggestion is to take it to a shop so they can put it on a scanner.

[Rio_Grande]

It is mpi with 1 injector into each port. Injectors are definitely a possibility. Shops are how alot of the earlier parts were tossed at it by their recommendation including the fuel pump. Not sure if they replaced the screen, I can't remember if they just put a pump in or a unit. This is the 3 rd fuel pump on this jeep at 120,000 miles. I will check the pressure tomorrow I need to make an adapter for my tester. I ran the codes and the only thing I had was the battery code.  I would love to drop it off and get it fixed but the shops I trust often call me on jeep issues they can't figure out. This one is whooping me.

[Jeffy]

you have a TBI so i'm not that familiar with the computer on those, however i would start by checking the fuel pressure. If you replaced the pump you should also replace the filter if you didn't. Could be as simple as a bad injector (you only have 1) or some bad ground or connection, can also be as complicated as an ECU problem. My suggestion is to take it to a shop so they can put it on a scanner.

It's a 97 not 87.

[sharpxmen]

It's a 97 not 87.

oops, misread that.

[Tr00b]

Oxygen sensor... If its skinny like a pencil its original and probably not working right. Makes a BIG difference, especially for the "when its cold" stumbling and etc.

Also, clean your Intake air temp sensor. Its a one wire sensor thats on the intake runner closest to the driver. They get gooped up with PCV and can cause issues.

The downstream O2 from the cat is not as important and can wait. Having the exh mani cracked I think messes with the upstream O2 and burns them out (don't quote me on that, but my O2 failed shortly after the exhaust mani cracked)

[Rio_Grande]

Thanks I will try it. I got it out tonight after new front end parts and steering box. Still can't run over 45 as it walks all over at that speed but that is another issue I may post up!

Tonight when I would get it to 45 ish and stomp it, it just kinda Boggs out and won't take off. I even down shifted and while it revved higher I got the same bahhh response. Wonder if ther aren't cat issues too?

[sharpxmen]

check the fuel pressure, you said you replaced the pump which means it should be good but doesn't hurt to check.

[Rio_Grande]

Had some time today

The stumbling and backfiring issue stops as soon as the 02 sensors kick in. I verified this today with my scan tool. 02 sensors all read out below1.0 while running with an occasional spike over on the rear.

What I found disturbing today was when I first started the jeep cold it read -64 for the timing. This has kinda acted like a timing issue all along, but when the O2 sensors kicked back in it ran fine. Now I still have a lack of power at top end, but I am going to check that closer in a bit with my new back pressure gauge. I just need to find a tip for it. The gage is made to be installed in the 02 sensor holes. I want to drill a small hole in the pipe and then plug it with a screw or weld it shut. I don't want to mess with the sensors unless they are bad.

Gonna clean the air pressure sensor as well.

[sharpxmen]

there's nothing to clean on the MAP sensor, just make sure the fitting is not plugged

sounds to me like you have a fuel pressure problem, when it gets in closed loop it's being adjusted by the o2 feedback - check the fuel pressure (unless you have some plugged injector or more than one sound to me like the pressure is the problem you're having).