2004 4.0 sputters under load

[HoHoDad]

About a month ago when I was out wheeling my 2004 TJ (4.0L/ automatic 4.56 on 33’s) started sputtering under load when in low range 1st gear. I thought it was going to die but it never did just sputtered along...It would do a few sputters then be back to normal... a minute or two later it would do the same thing. I don’t remember the RPMs but we were crawling over some bowling ball size rocks every few feet. One thing I did notice was that when the sputtering cleared and came back to normal there was a momentary increase in RPMs without any throttle adjustment. Anyway when we got to some normal trail I checked an it had not thrown any codes. other then when we were crawling over the rocks runs like normal. My first thought was maybe some loose or corroded wiring.. I have checked and cleaned all the connectors and I replaced the TPS with a new Mopar TPS as there had been some odd minor rpm's changes when stopped like at a stoplight. Thinking why not the jeep has 196000 miles. It is my daily driver, It does not have any issues like starting and runs like new. About three months ago I replaced the injectors, plugs and cleaned the throttle body. Yesterday coming home at 55-60 i went to pass a truck and it started sputtering.... there was no loss of speed just the sputtering, if I backed off the throttle it stopped... I have been unable to duplicate the sputtering. Since it has not thrown any codes I am thinking maybe fuel pump starting to fail? Your thoughts please I’m at a loss?

 

[Chris]

I hate throwing money at things and just guessing. I always encourage people in this type of situation to keep driving it, doing everything you can to make it sputter. Eventually, a check engine light WILL come on, no doubt about it. That will tell you a lot, and it's better than guessing.

When is the last time you replaced all the O2 sensors? They should all be replaced around every 80k miles. If they are going bad, they can cause things like this to happen.

If you do replace them, check out this thread first:
The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

 

[HoHoDad]

Thanks Chris... Like you I am thinking I will run it until it throws a code. a lot better then throwing money at it..

 

[Chris]

I totally agree. You can blow money really fast by just guessing. And truthfully, there's a lot of things that could make it a sputter. A slowly failing fuel pump, bad O2 sensors, CPS, TPS, etc.

 

[AndyG]

Catalytic converter is likely.

 

[RubiconRick]

I've had a very similar problem for 2-3 years now but never been able to totally find the cause. 2006 Rubicon. Similar symptom with the random sputtering but it will only happen going from idle to initial load. The check engine light also flashes but no codes stored. Garage ran out of ideas to check so I finally went to the dealership. They guessed for a while and that got expensive. new TPS, changed 1 O2 sensor they thought might be weak (there are 4 on this California edition rubicon). Finally 1 tech decided to measure the plug gaps. They were way off but otherwise in good shape. Swapped them out and the problem went away for almost a year. Its starting to come back again. Gonna start with plugs again but that seems weird since they are fairly new. The other thing I discovered recently is that I can reproduce the issue if I sit at idle in neutral and then step on the gas firmly. It will sputter every time and the engine light will flash. If I accelerate slowly it doesn't happen. Once I am under load the issue doesn't happen at all. This problem is very bad when taking off from red lights obviously and I have stalled in the middle of the intersection a couple times.... Any ideas?

 

[RubiconRick]

one of the trips to the dealer they also checked/ cleaned the AIC but that didn't change anything with the issue. The light that flashes is the little orange engine light but it doesnt stay on and there is no code recorded. It may be my imagination but the humidity might play a factor as well. In summer when its hot and dry the problem is less likely to happen. Right now in December when its damp here and near freezing I can reproduce easily by stepping firmly on the gas while in neutral. When the sputtering happens, the gauges go wild, the RPM drops from around 750 down to 200 and then jumps up to 1300 RPM (if it doesn't stall out). Also, if it does stall out, it often wont restart unless I remove the key and put it back in. Then all is normal again. I love my jeep but this can be a safety issue when it stalls out in the middle of an intersection. My son will start driving in a year and a half but I don't feel comfortable letting him go anywhere while its doing this.