Fuel pump or O2 problem? Updated! More advice needed.

[geopig]

Hi all,

I've just started having some issues with my 91 YJ (fuel injected 2.5L) this weekend. Here are the details/chronology of the problems:

-Saturday morning the jeep wouldn't start, turning over but not getting fuel it seemed like. Waited a few minutes and it started up no problem.
-Driving to Yosemite NP from LA, and on slight uphills doing 70-75 MPH short (a second or two) loss of power 2 times during the trip.
-I stopped for grub after driving ~250 miles and when I went to get going again, no problem starting but it stalled and died after a minute in the parking lot. I was rolling so I bump started it again no problem.
-Sunday morning wouldn't start. Tried a couple of times waiting a minute or so between tries and it started after 3 or 4 tries.
-Monday on the way home from Yosemite, stopped after ~150 miles for a drink and wouldn't start. Had to try 4 or 5 times with time in between tries but it eventually started.
-One short loss of power under the same conditions as above on the way home.
-Stalled when back in LA, when driving slowly after exiting freeway in front of a friend's house. Started up after we got his gear out of the jeep which took maybe 3 minutes.

So I'm thinking that the fuel pump may be going or there is a problem with the O2 sensor. I haven't had any warning lights come on at all during any of the problems above. I've also been using good gas and regularly (once per month) put some FI cleaner in the gas. Just wanted to see if it may be anything else. I'll start by replacing the O2 sensor and hopefully it will solve the problem but any additional advice/suggestions would be greatly appreciated. Thanks for reading the long post.

[hi_c]

I'd go even cheaper than that, by starting with replacing the Fuel Filter. Also, have you ever had to drop your gas tank and replace the fuel sock and/or sending unit? If not, then now might be a good time to drop it. It's pretty simple.

Try to run the Jeep out of gas (dropping a full tank would not be fun). When the Jeep is on "E" drop the tank. There is a mesh filter called a fuel sock that goes over the end of the sending unit inside the tank. It's like $4 from the dealer, get one. Also, there is a rubber o-ring that mates the sending unit to the tank. IF THIS O-RING IS BUSTED, THEN THIS IS PROBABLY YOUR PROBLEM. See, (I have 89 2.5L TBI also) the system needs to pressurize fuel so that the next time you start up, the fuel will be at the TB before it cranks. If there is a leak in the seal, you might not be pressurizing. But after trying several times, it might pressurize enough to get you started. I would replace all this first. If your O2 was bad, you'd be idling rough and probably out of range (over 1200 or under 600rpms).

I did this about a year ago and it solved my issues which were similar to your symptoms. When I took the old fuel sock off... it was so deteriorated that when I touched it, it fell apart in my hands.

Good luck, and let us know what you do.

Corey

[geopig]

I will try the fuel sock and sending unit replacement. I just replaced the fuel filter ~3 months ago so theoretically it should be fine. Unfortunately I'm pretty full on gas right now so I'll wait until it's near empty.
Also, I checked constantly and I have no fuel leaking at the rear. I don't know if the ring was busted if there would be enough fuel to leak to notice it on the ground. Thanks for the advice hi_c!

[hi_c]

If the o-ring is busted, it probably won't leak gas, but rather air. Yes, air. You need the air tight seal to pressurize the line. Otherwise there's no pressure keeping the fuel in the line and it will all empty back into the tank, thus not reaching your throttle body.

Also, I didn't mean replace the entire sending unit. I would bet that it is ok since once the Jeep starts, it's relatively ok. I was just asking if the tank had ever been dropped for work. I would just replace the o-ring and the fuel sock. Together, they should only be about $10 from the dealer. Go ahead and order them, cause they might not keep them in stock.

corey

[geopig]

Yeah, I got you but forgot to put "O-ring" in front of sending unit in the last post! Sorry bout that. That sounds exactly like what is happpening. When I leave it, say overnight and try to start it won't. But on the second or third try it will and then there is no problem, so it seems like the line is draining to the tank. I'll do the O-ring and sock replacement when I'm empty, which probably won't be for a couple of weeks since I'm heading out of town for a week in a few days.
Thanks again Corey!!

[geopig]

So today I'm driving home from school (which is only 10 miles) after having the same starting issues (needed a couple of tries to start) then just a few blocks from home it stalled and now won't start again. Also, I just replaced the plugs, wires, cap and rotor about 3 months ago.

So is it possible that it is still the O-ring at the sending unit (suggested by hi_c) or does it sound more serious now, like the fuel pump is shot? Opinions gladly accepted!!

[XJNick]

Hi,

Can you hear the fuel pump running when the ignition switch is in the RUN (not start) position? If not, is there 9-12 volts present at the fuel-pump with the ignition switch in RUN?

To my knowledge, a bad oyxgen sensor would NOT cause a no-start condition.

-Nick

[geopig]

Hey XJ

I can hear the fuel pump come on when the ignition is in the run position, it doesn't continually run but I'm almost 100% that it shouldn't/didn't before. Correct me if I'm wrong on that one. I can hear it power up for a second or two. That makes me think that the fuel pump is ok, unless the pump is not working sporadically which I suppose is possible. I don't have a meter to test the voltage additionally, and I haven't dropped the tank which is full right now. Just for clarification from hi_c's post above, I'm pretty sure that my 91 YJ has the MPI fuel injection system not the TBI (at least is says so in the Haynes manual).

With regards to the O2 sensor, based on other posts I think I should have a rough idle and other power issues if it was, so I agree that it probably isn't the 02 sensor.

Any other thoughts??

[Snitty]

Unfortunately I'm pretty full on gas right now

well if a full tank is unfortunate, feel free to send it all to me... i won't charge much for the convenience