[The Shape]

Today I drove about an hour with the A/C blowing, 97 degrees outside temp. After driving that long on the highway when I got into town every time I stopped at a light it would stumble like it was misfiring as I took off. It would clear up as soon as I gave it a bit more throttle and then shift an accelerate perfectly until the next stop light or stop sign. It's an Auto trans, plugs are brand new and properly gapped about 7k miles ago. Any ideas?

 

[Saxdogg]

Mines the same. It has a slightly lopey idle but runs perfect otherwise. No vacuum leaks I could find or any codes so I've just ignored it.

 

[Kyle.Roth]

I have the same problem with my 98' 4.0 L Manual. During acceleration stumbles at full throttle between 1,000 and 1,500 RPM.

Any body have a solution?

 

[mrsuthern]

Check cleaning throttle plate. And possibly cleaning MAF with sensor safe cleaner. Easy to do starting points no scanner needed. Could also try cleaning the IAC also come to think of it

 

[AZ01TJ]

I have the same problem with my 98' 4.0 L Manual. During acceleration stumbles at full throttle between 1,000 and 1,500 RPM.

Any body have a solution?

Drive like it's a 19yr old vehicle & stop flooring it. Also, give it a complete tune-up.

 

[Backwoodsraider]

check spark plugs. had similar on a 97 Cherokee.

 

[Outdoorzman]

If you have a clean Throttle Body, clean, properly functioning Idle Air Control motor, Throttle Position Sensor is good and you have no codes, you could be having an issue with fuel delivery. Assuming, all of your other tuneup components are in good condition (meaning: new or close to it).

On the 4.0 engine, I believe there is a TSB for insulating one or more fuel injectors to avoid heating them up and vaporizing fuel. I'd also recommend checking fuel pressure at the rail and determine if you have a potential regulator or fuel pump problem.

There are a whole host of other possible issues, but at the age of these vehicles, if you are operating on the original fuel pump, you've gotten many hours worth of work out of that device. Between the fuel pump, check valve, fuel pressure regulator and injectors, it's another part of the drive train to test.

 

[Kyle.Roth]

Thanks for the info.

I ordered this TJ from the factory. Have all the receipts.

If anyone has this problem and fixed it, please share.

Every 3k; GTX 10w30, Fram -16, Lucas injector cleaner, and lube grease points.
Every 25k; cap, rotor, and E3 plugs. Wire set is Auto Zone life time warranty.
Air filter as needed depends on trail conditions. Even carry a spare.
In the past year; both O2 sensors, fuel pump, fuel filter, fuel regulator. Accel Coil.
Intake side is all stock.
Exhaust side; Borla shortly, stock cat and muffler.

No header / intake gasket leaks (as far as I can tell). No leaks in exhaust until the muffler.
No vacuum leaks.

Injectors are not protected from heat. Will investigate.
I can't think that the sensors mentioned could have problems without spending error code.

This weekend I'll do the following and report back;
Accel wire set.
Air filter.
Clean throttle body with spray cleaner.
Check fuel pressure.

Thanks again.

 

[Kyle.Roth]

Regarding full throttle....

Lol.

I'll explain. Traffic permitting, ease out clutch, floor it until 2500 to 3000 rpm. Shift and repeat to the speed limit. Then straight into overdrive (5th).

Obviously on trails, throttle as conditions require. Crawl rocks, go like hell through mud pits.

If you come back clean, you loose.

 

[Kyle.Roth]

Regarding TSB. I searched NHTSA.Gov. They have all manufactures communications. Chrysler has 62 TSB and six recalls for the '98 TJ. Not one mentions injectors.

Thanks again.

 

[wildrnesxperienc]

That injector TSB starts at model year 1999. I'm assuming your exhaust manifold is the one piece manifold. The two piece that was introduced later lets heat from the cats and muffler rise up around injector 3 causing the fuel to vaporize with heat soak on hot days.

 

[Evpjr]

Stop Using that CHEAP Ethanol, and start buying real gasoline!

 

[Kyle.Roth]

Thanks for the TSB info.

I ordered this TJ from the factory. All maintenance has been on time. Most of the work I did myself (Have a huge file of recipes).

Intake side all stock.
Exhaust... I have one piece Borla shorty headers. After header to tailgate all stock.

I'm gonna check for vacuum leaks, header/intake gasket leaks, clean MAS, clean throttle body and idle position sensor.

I use Lucas injector cleaner every three K. That is part of oil & filter change, Grease & Lube and Lucas.

About gas...
As Riggs said in LW 3, ugg Exxon!

 

[Kyle.Roth]

I have the same problem with my 98' 4.0 L Manual. During acceleration stumbles at full throttle between 1,000 and 1,500 RPM.

Any body have a solution?

I found the solution to my problem of stubmble between 1,000 and 1,500 RPM.

As AZ01TJ recommended "...give it a complete tune-up." "Complete" in complete tune-up I defined as; Plugs, cap, rotor and, wires.

The problem was actually traced to bad plug wires. The wire set was Auto-Zone's Lifetime Warranty wires. They didn't say who's lifetime in the warranty. They didn't say how often I would need to use the warranty.

I now have AC Delco's Lifetime Warranty wires.

What didn't solve my problem; (you know throw parts at the problem)
New Accel coil.
New Air filter.
Throttle body cleaned.


One last thing AZ01TJ. I still work my way through the gears at full throttle until 3k RPM.

 

[Rick58]

Thanks for Update....Glad its running better