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1997 xj running like poo

cmechsxj

NAXJA Forum User
Location
Avondale az
ok so first and foremost new here and I would like to say hello. This is like my 7th jeep and I love them this is a 97 Cherokee SE 4.0 Auto

now onto the issue. This jeep runs really rough at an idle and exhaust smells like fuel terribly. has a pretty good miss to it. now under throttle this thing makes good power and runs smooth will run down the freeway at 75 like a champ. when I first got the jeep home I had noticed that the throttle body bolts were all loose so I tightened them.

first off I have a cracked factory manifold I am going to replace this with a header (this could be part of the running issue perhaps?)

I have replaced the cap, rotor, plugs (W/Champion), wires due to it having cylinder misfire codes. reset the engine light and withing 2 days it was back on with the same code. Can someone please enlighten me on where i need to start looking next?
sorry for the long winded description any help would be greatly appreciated
 
The header is definitely part of the issue and should be addressed first since that is a known issue. Once it os replaced, then start trying other things. A cracked manifold can certainly cause an engine to run roughly.
 
How many cylinders are misfiring? Are any of them adjacent cylinders?

Post the EXACT codes here (not a description) for the most accurate replies. With OBD, the devil is in the details. The fact that you have codes and symptoms at the same time is not a coincidence. Gotta let the codes lead the way for your repair strategy.

Fuel injectors (swap the ones from misfiring cylinders and see if fail follows) and internal engine issues (run compression test on all cylinders) are also in play for misfires. The compression spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

Good luck and keep us updated!
 
Last edited:
How many cylinders are misfiring? Are any of them adjacent cylinders?

Post the EXACT codes here (not a description) for the most accurate replies. With OBD, the devil is in the details. The fact that you have codes and symptoms at the same time is not a coincidence. Gotta let the codes lead the way for your repair strategy.

Fuel injectors (swap the ones from misfiring cylinders and see if fail follows) and internal engine issues (run compression test on all cylinders) are also in play for misfires. The compression spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

Good luck and keep us updated!

the codes it is throwing is
P0300
P0301
P0302
 
the codes it is throwing is
P0300
P0301
P0302

The P0300 may be a clue.

That is a code for "random misfire" which means misfire is moving around. Anytime I see this code, I look for one common root cause for something upsetting the air/fuel ratio. That one common cause for the P0300 is often also responsible for the other select cylinder misfires which you have for cylinders 1 and 2.

That could mean a problem with fuel pressure or a major vacuum leak. I'd start with checking fuel pressure and get that new header installed. For a 97, you should have 49 psi at idle, plus or minus 5 psi.
 
so this is a little odd I go out with the jeep running and unplug injector 1 no change at all.
unplug injector 2 no change at all in running. every one of the other ones when unplugged makes it run way worse. do I possibly have a couple bad injectors?
 
Could be the injectors, their wiring, or spark, or (bad) no compression.
 
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