[Guest]

98 TJ/4.0 with 95K miles. Has been working fine. About 1 yr ago I started to have a strange problem, at highway speed it would suddenly quit excelerating, it would not die just not go forward. I would pull over for maybe a minuet and then drive on. It never left me stranded untill last week. I had to drag it home. I am thinking the fuel pump, however some one said to check the catalytic converter. Any thoughts? No check engine light.

Don.

 

[Olin18]

please provide us with just a little more information. When it would slow down on you was it under hard accel. Or just normal driving.
From what you have mentioned, I would say you would be wise to check your fuel filter. If the fuel pump was bad your jeep wouldn't run at all. But what you describe sounds like text book old filter.

 

[Guest]

Well the other day it was at highway speed, no increase in acceleration. However when I finally tried to limp off the highway, I could start my Jeep, it would idle fine, then when i tried to give it gass it would bog, no matter what the input, full throttle, partial throttle, or feathering the throttle. I tried all I could think of, please note that this morning after having sat for a few days I drove it around my parking lot. I wonder if this has to do with operating temp, so again back to the converter? I did not spell check this time sorry...

 

[2344]

Sounds like it could be an O2 sensor, but that normally trips the check engine light. maybe run the scan anyway to see if the light is just not coming on

Phil

 

[Guest]

O2 sensor? Why? Would you mind elaberating...
Thanks,
Don

 

[283]

Sounds like the fuel filter to me, also.

Ken Linzmeyer

 

[Guest]

Fuel filter!

Even if were wron its cheap insurance




Wheel on!

 

[Guest]

Another idea. Bang your exhaust, any rattling inside, especially around the muffler could mean an internitent blockage. If its OBDII then your cat or O2 would trip an instant check engine lite.





Wheel on!

 

[WILL]

Ditto, fuel filter. Put a bottle of STP fuel treatment in the tank too.

 

[2344]

I agree it should trip the computer,

as for why, if the o2 sensor isnt working, then the computer is getting incorrect readings about the lean/richness of the fuel air mixture, causing the symptoms that you are stating. The only reason i mentioned it is my wifes vehicle had the same problem, changed the o2 sensor and no problems.

Phil

 

[GeeAea]

The fuel filter in a TJ is an integrated filter/pressure regulator. You have to drop the tank ....and it ain't no $10 item.

 

[LEVE]

1. I agree, code recovery is a must,
2. It's the first place to start,
3. But an O2 sensor,
4. Should not cause de-powering.

 

[2344]

Well I dont know what you would call not beeing able to go the speed limit on the highway when you were previously able. Or then a few days later only beiing able to go on side streets because you cannot go faster than 25mph. The engine just wont push you faster.

Me I call that loss of power. Maybe my wifes car is a freak of engineering that once the O2 sensor went bad the engine decided to take a nap.

Phil

 

[RRich]

It does sound sort of like an O2 sensor, but it wouldn't be as bad as you describe. It'll run bad, but not to the point it can't be driven. Even totally disconnecting it, it'll still be drivable.

If it was Fuel, or lack of it (pump, filter etc.,) you should also be complaining of backfiring.

Sounds like exhaust - a loose baffle in the muffler or cat can do it. Something causes it to move, it blocks the exhaust flow, then eventually falls back out of the way - a real hair puller!)

Hook a vacuum gauge to manifold vacuum - then put the gauge inside where you can see it while driving.
Hopefully at first it'll be running fine - note the reading at idle - should be about 17+.
Watch how it reacts when you drive it normally.
Then when it "happens" if the vacuum is way low, doesn't bounce back when you decelerate - it's exhaust.

You might have to call around to find a vacuum gauge - diagnosing by vacuum is rapidly becoming a lost art. Everyone thinks the computer can "do everything." Not so, the computer can, sometimes, give a clue.

Then of couse it can be something simple, like a loose coil wire - have a close look. Start there.

 

[LEVE]

In reply to:

Me I call that loss of power.

[/ QUOTE ]1. Look... I'm not denying the Jeep is de-powering.
2. I'm not trying to get into a flame war with you.
3. I'm not trying to say you're and Idiot and I'm not...
4. I'm only trying to help you.
5. But I did try to tell you that the 02 sensor,
6. Likely wasn't the culprit,
7. Despite the code.
8. If I offended you,
9. that was not my intention.

 

[RRich]

Sorry, LEVE's right. You can disconnect the O2 sensor.
O2 sensors have an influence over the ECM, but not a profound influence.

Most anything can set an O2 code too - a bad plug wire will - misfire in a cylinder puts too much unburned O2 in the exhaust, the sensor sees the abnormality and sets a code.
Codes just are clues, not specific.

Your wife's vehicle - you didn't say what it was. A GM?
Many GM's, and some others, have a back-up PROM - when the ECM "sees" a failure, like the O2 sensor, it goes into "back-up mode." Instead of using sensor information, it substitutes standard readings that'll keep it running till you get it fixed. Run, but not great, goes full rich, timing goes to a set value. Mileage & performance suffers, sets code.

But - if the Cal-Pak or back-up PROM isn't working, it just shuts down when it tries to switch over. When you try to restart after turning the key off, it again tries to run on the main circuit, until it detects the failure again and tries to go into back-up.
A new O2 sensor stopped it from going into back-up.

Sonme ECM's don't have a replacable/removable prom for this, they do it internally - you get to replace the entire ECM.

That may explain your wife's vehicle. Or maybe not.

 

[2344]

Well it sounded simaler to my wifes situation so I thought I would throw it out there.

In her case it was fairly severe, but like I said It may be an exception, I really dont know.

Thought Id pitch in,
Sorry if I am wrong.


Phil

 

[jdoggmoney]

Are you kidding me? No other in-line filter? IMO... very poor design!

If this is true, it's time also to check fuel pressure/volume. Many electric pumps die slowly as you have described over time. I think a Haynes/Chiltons will have the numbers and you can get a gauge fairly reasonable at one of the local chain parts store.

For starters you may just safely park and chock the Jeep the next time it acts up and crawl underneath to listen. You may be able to hear the pump pulsing or cutting in and out.

Good Luck!

 

[Guest]

To all you guys thanks!!! I read some stuff in my Jeep book, about testing the fuel pressure etc, the vaccume info is cool thanks again. Can I check the fuel pressure with a tire gauge, I know its not the correct, too but will it work?

I will try all these ideas... Again my thanks and please dont argue over my silly problem.

Don

 

[LEVE]

In reply to:

Can I check the fuel pressure with a tire gauge, I know its not the correct, too but will it work?

[/ QUOTE ]1. Pressure is pressure,
2. But I wouldn't advise it.
3. EFI Fuel pressure testers aren't too expensive,
4. And you'll need one again...
5. So pop for one,
6. You can never have too many tools.
7. May I suggest This or This...?
8. But again, I doubt it's a fuel related problem,
9. Because it's dying so darned quickly,
10. I'm still convinced it's electrical,
11. But I've been wrong before,
12. Oh, if you do test the fuel pressure...
13. That only tells you it's good during the test.
14. That does NOT determine if it's good all the time,
15. Like under engine load.
16. And that's really when you need to do the test...
17. It kinda puts ya in a bind.
18. I don't recommend running the gauge into the tub,
19. And driving around...
20. That's an accident waitin' to happen.
21. So you need to "T" the line and add,
22. An electric sender and gauge.
23. The you know the constant state of the EFI pressure.