• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Help needed w/new mystery stumble - fuel? electrical?

MassMopar

NAXJA Forum User
Location
MA
98 XJ 2-door, 4.0, 5 speed
Just got back from vacation, so the jeep sat for 2 weeks
Warmed up for 10 mins, drove 5 miles to work just fine.
Drove 5 miles home just fine.
Later that day, drove 2 miles to grocery store fine, loaded up, then heading back it starts acting up.

I get 1/2 a mile from the store, taking off from a light, up to 2nd gear, between 1 and 2k RPM, feels like a loss of power, like I'm out of gas. Motor doesn't respond to the gas pedal like usual, sort of stumbles but never dies. Clutch out, rev it up a bit (2k rpm, nothing crazy), again not behaving right, like it's trying but not succeeding. Like it's getting some gas but not enough. Pull over, idle stumbles to 500, 200. Clutch out, rev it up a bit again, starts idling normally (700-1000). Drive 100 ft, feels ok. Never once dies. I sit and let it idle for a minute or two, then take back off for home. Remaining 1.5 miles to home, acts normal, pulls strong with normal power up to 3rd gear, no issues, except for 1 more small hiccup which I felt but didn't see on the tach.

All gauges fine, no idiot lights, no codes, no chimes. Nothing prior to indicate an issue.

I couldn't isolate the problem to anything specific while I was driving -
I have a full tank (filled 2 weeks ago just before i left for vaca from my normal reliable gas station). Gauge still reads full.
It didn't seem to do it in a specific gear or under a specific load or at a specific RPM.

Possibly related- When I shut it down after driving across town, I can hear a considerable amount of "flushing" noises coming from the fuel tank area. I've been under the entire jeep, all the fuel lines look great except for 1 short one is pretty corroded near the tank. Nothing's leaking so I assumed it's not an issue. I asked NAPA if they had a fuel filter for the jeep and they said it was internal to the tank so I haven't bothered with it.

I have ~125k on it.
I'm not getting any codes.

What do you guys think?
Do I have a fuel delivery issue?
Do I have a sensor going bad?

How does it behave if I'm losing a crank or cam position sensor? In my 00 Dakota, when my cam position sensor was going bad, it would randomly kill the motor out of the blue, then fire up again 5 mins later like nothing happend, but it would throw a code.

TIA, sorry for the book :rtm:
 
Last edited:
You need to put a pressure tester on the fuel rail and see if the pressure is about 49 psi, and see if holds with the engine turned off. If the pressure drops, the fuel line in the tank on the pump may be bad (causing the noise), or the pressure regulator is bad.

A bad, loose honeycomb in the Cat can cause it too.

CPS can be going bad, or may need cleaning (metal dust from the clutch on the sensor tip. Or the TPS may be going bad.
 
TPS = Throttle Position Sensor mounted on the throttle body. It is an electric sensor that senses throttle position.

Most auto parts stores will loan a fuel pressure tester out for free (with a deposit).
 
When my 92 5 speed has a stumble while accelerating between 1 and 2 k that felt like power loss, it was the upstream o2 sensor like Jnida63 said above.

It would do it a couple of times after starting up and then clear up after a few minutes when it got warm.
 
Dunno what the Jeep's problem is, but don't worry about that flushing / gurgling noise. There is a TSB on that issue, basically they sell you a check ball that goes into the vent pipe assembly if I remember. You drop the tank & replace some add some parts in the filler.
As for the stumbling / intermittent suckyness... It's probably either fuel or spark. Do you have a volt meter? know how to use one? Could be your friend here.
 
Sounds dumb, but my Transfer Case was darn near bone dry when I had a problem like this... Took 1.25 quarts to fill it...

That would violate the "Dem Bones" rule of diagnostics! :party:
 
Ordered a couple new O2 sensors from Rock Auto. I've had a hell of a week and since I don't DD it I haven't had time to check the fuel rail pressure. How hard is it to drop the tank, and are there any parts in there I should be replacing? My goal is for this XJ to be as reliable as possible - 125k on it now....
 
I bought both NTK O2s from rockauto last week for ~$75 shipped. It's still on the first tank, but looks like the gas mileage is up.
 
This is going to sound crazy, but I've had similar issues that just pop up sometimes & fix themselves two weeks later. I suspect fuel quality / contamination issues but haven't been able to pin anything down.
Check your MAP sensor & wiring, too. Wiggle things around. I've heard dealership techs talk about a common wiring issues where the MAP sensor signal wires rub on a head stud...
 
If it was the upstream O2 sensor, wouldn't it throw a code?

Most of the time they do not throw a code. You may have lost the 12 volts feed (relay, fuse) to the O2 sensor internal heater (or the heater in the sensor went bad), that keeps the O2 sensor hot enough to work at idle.
 
Most of the time they do not throw a code. You may have lost the 12 volts feed (relay, fuse) to the O2 sensor internal heater (or the heater in the sensor went bad), that keeps the O2 sensor hot enough to work at idle.

DISCLAIMER: I have "Oldtimers" disease.

As a note, I can't really remember the last time I saw an upstream o2 sensor code. Lots of downstream sensor codes, but upstream sensors tend to fail slowly and not throw a code in my experience.

Or, at least that is how I remember it. I think. :dunno:
 
Well I snapped the bung out of my cat, so I've got a couple rock auto specials on the way... new front pipe and a cat. Didn't look like it would hold up to welding that bung back on lol
 
I finally got around to doing the exhaust this weekend. New front pipe, new cat, new upstream & downstream O2 sensors. Everything came out easily with a sawsall except the bolts at the manifold flange. Snapped one but got the other un-done. Took a cutting wheel and cut them both off, drilled them out, and put some nice thru-bolts in there. The only real issue I had was the walker gasket I bought from rock auto was too small to fit the flange, so I picked up some copper exhaust gasket maker and tuned-up the old gasket. So far so good, no stumbles on the trip around the neighborhood last night or on the way to work this morning.

What other sensors should I be gathering up for replacement soon (125k mi)? TPS? Crank PS? Cam PS? All of the above?

Thanks for the help guys
Nick

IMG_20130609_185854_966.jpg
 
LOL:

What other sensors should I be gathering up for replacement soon (125k mi)? TPS? Crank PS? Cam PS? All of the above?

YES!!!!

Congrats on the fix!!!
 
Just wanted to update. Made a July 4 300 mile roundtrip in it, no issues whatsoever with stumbling, ran like a champ. This is after doing a new walker downpipe, walker cat, and new Bosch up and downstream O2s. Thanks for the suggestions all :viking:

IMG_20130702_150752_904.jpg
 
Back
Top