Jeep Enthusiast Forums banner

Stumble on Acceleration?

4K views 14 replies 6 participants last post by  Holm-z 
#1 ·
Ever since I bought my 2004 Rubicon 4.0L with Automatic it's have this thing where sometimes when I'm out of stoplight and I go to take off it's like it stumbles for just a moment. It's done this ever since I've had it and it's had a complete tuneup, new plugs, etc, etc. and all kinds of other work done to it and yet this has never stopped or changed in any way.

My CEO is not on and there are no codes for pending code stored in the computer if it's checked with an OBDII reader.

My big brother is of the belief that it it is likely one of the sensors on the intake side of the engine but that's just his educated guess and with no codes he has no idea which one and it would be expensive to just start buying and replacing them hoping to get the right one.

Has any other owners experienced this and did you figure out what caused it and how to cure it?
 
#2 ·
In case it helps anyone help me diagnose my problem here's a list of everything maintenance wise that has been done since I bought it;

New WIX air filter.

Oil and filter have been changed every 3500 miles using WIX filters and Valvoline Durablend 10W40 oil.

New Mopar oil pressure sending unit.

New Bosch fuel injectors.

New Mopar feel injector heat shield wraps on all the injectors.

New iridium spark plugs. I forgot the part number but it's the one that Jerry Bradford here on this forum recommends for 2004 models.

New high extra high capacity battery installed. I forgot the brand but is the one that SouthernGypsy here on this forum recommended.

Every plug under the hood, well really on the whole Jeep that we could get to has been systematically disconnected one by one checked for corrosion and had synthetic dielectric grease brushed in the connector.

New Mopar temperature sending unit.

New Murray OEM replacement radiator.

New Murray water pump.

New Murray older pulley.

New Murray tensioner pulley assembly.

New Gates premium belt.

New Gates premium perfect-fit upper and lower radiator hoses.

New WIX transmission filter and Valvoline ATF+4 fluid.

New PSC dual transmission/power steering cooler.

Power steering system completely flushed through with new Valvoline ATF+4 fluid.

Front and rear diffs completely drained and refilled with Valvoline durable and 75W140 differential fluid.

Brake system completely flushed through with new Valvoline DOT 4 synthetic brake fluid.

Front mini-cats and large rear catalytic converter's all removed so now the exhaust is a streak system other than the stock muffler.

Poison spider hood louver kit installed to help vent off excess under hood heat (plus it looks cool).



I feel like I'm forgetting something but if I do remember something else I'll add it later.
 
#5 ·
Jerry Bransford said:
How well does the engine idle? Does the stumble happen all the time? Just when cold? Only when warm? At this point my initial suspicion would be a bad TPS (throttle position sensor) or less likely, a dirty IAC (idle air control).
The engine idols good normally. I think I tend to notice the stumbling more when it's warm then I do when it's cold. I think I've also felt it once or twice when it was cold or at least not fully warmed up as well but not as much.

That something I forgot to mention that we did on our list my brother did a seafoam treatment on it. Had the exhaust just blowing white smoke out for like 10 minutes. But before he did that he got in there with throttlebody/sensor cleaner and really went to town on everything in the throttlebody to make sure everything was clean and there was no clogs or blockages. But that didn't change anything.

We have not done anything with the throttle position sensor I mean we haven't changed it so it's still the original.
 
#6 ·
AftonJeeper said:
:thumbdown: You should be getting codes from the O2 sensors if this is true.
Nope. No CEL light and no codes. The people at the muffler shop said they've done several of these models and have never had a problem with codes or the check engine light coming on. Only with some (but not all) of the later (JK) models and they even knew how to solve the problem on those.

Removing the cats improved the overall throttle response and noticeably reduced the heat under the hood near around manifold but did not solve or in anyway affect this stumbling on take-off problem.

We just talked about the cats in the "gurgle, gurgle, gurgle" thread if you want more info about that.
 
#11 ·
Put the cats back on... Id10t.

Check fuel pressure and an analog volt meter or a graphing multimeter pinned into the TPS will tell you if there's a flat spot in its sweep. Should start at around a half of a volt with the throttle closed and should be about 4.5 volts at full throttle. Do this test with the key on and the engine OFF. SLOWLY sweep the throttle blade all the way and watch the voltages while you do it. Voltage should climb steadily and evenly. If you get a spike in voltage (short) or a dead spot (open) then replace with Mopar TPS.
 
#12 ·
Update. I changed the TPS with a brand-new mobile or unit, and we cleaned the IAC it looked good to begin with but we want to head and cleaned it since the tip was a little bit black.

The idle is a little bit smoother overall but I'm still having a little bit of a stumble followed by a search on take off.

My brother says that my fuel rail does not have the connector on it that allows us to test the pressure with the gauge that he has.
 
#14 ·
Update. I changed the TPS with a brand-new mobile or unit, and we cleaned the IAC it looked good to begin with but we want to head and cleaned it since the tip was a little bit black.

The idle is a little bit smoother overall but I'm still having a little bit of a stumble followed by a search on take off.

My brother says that my fuel rail does not have the connector on it that allows us to test the pressure with the gauge that he has.
The fuel pressure can be checked with easily but not from under the hood. Under the driver side just inside the frame rail you'll see where the braided fuel line snaps onto the hard line. Use a T fitting with the pressure tester and check it that way.
 
#15 ·
My upstream o2 sensor went bad but didn't send any codes. Try unplugging it (you will gets code when you do that) and see if it runs better. If it does, then that's your problem.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top