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i would really like to know how to fix this

G

grizzlypaugh

NAXJA Forum User
Location
Boring OR
I have a 96 Cherokee 4.0 HO. I have replaced the cap, rotor, wires, plugs, TPS, IAC, and both O2 sensors. I have cleaned my TB, and replaced Fuel filter.

Ok, so my jeep has been running bad for awhile, and I cant figure out why. I can not use full throttle, it bogs down when i put the peddle down.If i lift up an 1/2" it doesn't.

Then when it has warmed up and i shut it off, if I start it back up about 10min later it coughs and back fires and i have to pump the peddle to get it to rev up enough to where it quits coughing and runs.

Then when I'm wheeling, its way worse it does exact same thing but some times i cant get it to clear up and it dies. Then i have to wait for like 45min then it will start and clear out and run. Any help would be great!!
 
Check your battery voltage when it's bogging down - have a helper measure the voltage right at the battery. If it's at or below 11 volts or so, you should check your alternator and battery. I had a marginal battery that shut me down the first time I floored it after starting in cold weather, it started up about an hour later just like you described and ran fine once I warmed it up.

Also, are you sure it's full throttle, or just under a large load? Try going full throttle with it in neutral for a moment and see if it bogs down. If it does, it's the full throttle issue... if it doesn't, then it may be the drivetrain moving and pinching a cable or hose somewhere.

Check fuel pressure at the rail also, and see if you have vapor up there - you have a 96 so they're not as heat soak susceptible as the 00/01 models, but it's still possible.
 
kastein said:
Check your battery voltage when it's bogging down - have a helper measure the voltage right at the battery. If it's at or below 11 volts or so, you should check your alternator and battery. I had a marginal battery that shut me down the first time I floored it after starting in cold weather, it started up about an hour later just like you described and ran fine once I warmed it up.

Also, are you sure it's full throttle, or just under a large load? Try going full throttle with it in neutral for a moment and see if it bogs down. If it does, it's the full throttle issue... if it doesn't, then it may be the drivetrain moving and pinching a cable or hose somewhere.

Check fuel pressure at the rail also, and see if you have vapor up there - you have a 96 so they're not as heat soak susceptible as the 00/01 models, but it's still possible.
Click to expand...

I changed my battery and alternator 3months ago. You think i should still check?

When I am driving and I floor it it bogs down but still accelerates while bogging, and when idling it does not bog.

Ok how do I check the fuel pressure at the rail? and how do I check for vapors?
 
Interesting... I would bet on the battery/alternator being OK then.

You can check fuel pressure at the rail by putting a fuel pressure gauge on the Schrader port on it - it's somewhere near the front end, looks exactly like a tire valve stem. The :gee: method of checking to see if your pressure is ok while driving is to masking-tape it to the outside of the windshield and drive around a bit while watching it. I'm not sure on the numbers, but I believe you want somewhere around 40+ PSI. If it dips noticeably during heavy acceleration you can bet on either your fuel pump being weak, your pressure regulator being on its way out, or maybe (hopefully) a clogged filter.

To check for vapor locking, you can turn the engine off (or simply don't start it back up when it would show the restart issue) and use a screwdriver to push the valve in the schrader port down. If some vapor comes out before you get gas, there's your issue.
 
sounds like a bad fuel pump or a problem with the fuel pump assembly(cracked hose on the pump, clogged pick-up).
 
96+ fuel pressure should be 49 psi.

Put a vacuum gauge on the intake manifold and rev up the engine slowly. If the manifold vacuum drops you have a restricted exhaust.
 
Make sure the motor can breath properly. Check for any blow-by issues, and make sure your exhasut isn't clogged.

My MJ was doing something very similar. Turned out the stuff inside my cat was breaking apart and blowing into my muffler - clogging it up.
 
A plugged cat acts like that!
 
Do a search for heat soak. Its a fairly common problem and there was a TSB issued.
 
grizzlypaugh said:
ok sweet i am so glad that you guys are helping me here, i am gonna check the psi and look around the fuel pump and check the lines.
Click to expand...

does it still have the oem cat convertor? could be clogged causung too much back pressure.

unfortunately, the fuel pump assembly needs to be pulled from the tank to check for a cracked hose or clogged pick-up. check fuel pressure with a gauge. i would also check pressure while under load when driving.
 
Ok I will pressure testing, and compression testing, and when it first started to do this stuff I tore out my cat took out the guts cause it was all broken and i didn't have the money for a new cat, and it ran the same didn't do anything. I am planning to get a new high flow cat and muffler next year.

What is heat soak? And TSB?
 
TSB = technical service bulletin, they were passed out by Chrysler to dealerships. Basically recalls and other modifications they found necessary to fix problems with the vehicle design after selling them.

Heat soak is an issue usually caused by the pre-cats on the 2000 and 2001 model years, but also affecting other years occasionally which causes the fuel injection system to stop operating as intended when the fuel rail gets too warm and the fuel vaporizes in it, leaving a "vapor lock". On vehicles with the fuel pressure regulator somewhere other than the end of the fuel rail, it's hard to get rid of the vapor lock, but with the pressure regulator the vapor gets flushed out and back down to the tank. I'm kinda surprised a 96 would suffer from this, from what I know 96s have a fuel return line and the pressure regulator was moved to the top of the pump assembly on the tank in the 97 model year, but apparently my info was wrong or something else is at work here.
 
Check your cat, that would be the easiest fix of them all. After that I would work towards fuel pump, lines, ect.

My engine had the heatsoak problem as well (It is an 00)
It sounds pretty similar to this problem but really only affected me during the summer months in 80 degrees+ weather.

Also the heatsoak problem always cleared up after a few pumps of the pedal. Yours does not seem to.

If it isnt your cat, then my money is on the fuel system.
 
Last edited:
Read thread before commenting, he's not running a cat at the moment.

You never mentioned air filter in your list of things changed.
 
The really important thing to take from these replies is to check the various systems instead of throwing new parts at the problem......
 
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