So I have a 98 cherokee 4.0L 4x4 auto, whenever I try to accelerate when the motor is cold or luke warm it starts to lose power and then there is a popping noise under the hood. It happens when heading to work, leaving work for lunch and when coming home from work. Also if I stop at a fast food place go in and eat (maybe 20 min) it will do it as well, basically the motor doesn't have to be all the way cold just slightly cold. It only happens for about 30-60 seconds then it's good from there on till the next cool down. If I let it sit and idle till warm I'm good but the motor will idle rough for about 60 seconds, sometime between cold and warm, then it's fine.It will not set a check engine light either. I've installed new plugs, wires, cap, rotor and cam pulse pickup sensor. So I have no idea right now

 

Bump for some help

 

Get codes scanned .

 

There are no codes. For some reason this problem will not set a check engine light

 

Did you have it checked??? Just because the CEL isn't on doesn't mean it doesn't have any stored codes.

 

Ok so I had it scanned and no Codes are stored. Nothing in the history or pending.

Also I changed the idle air control valve, throttle position sensor and the battery a few months ago too.

 

Just keep throwing parts at, no need to do any diagnostic tests such as checking the fuel pressure.

 

Well I wanted to get the basics out of the way. And can you elaborate on how fuel pressure would cause this on only cold to semi cold start ups?

 

Thought I would mention my 97 has been doing the same thing. I too have no codes, though I have not scanned it yet. I checked my fuel pressure this evening and it was 20 psi cold and 28psi at idle normal operating temp. Supposed to be 49, +-5 psi. Giving it throttle brings it down to 22psi. Also fails pressure drop test but just barely. I'm really thinking weak pump or clogged filter. Current pump is approx 5 years old 75,000 miles from Advance. Going to scan tomorrow then based off that pull trigger on new pump/filter assembly.

 

A cold engine requires more fuel, a weak pump won't keep up with demand and the engine will be starved for fuel and the you will have misfires with a load.

 

Ok that would make sense I'll have to test it this weekend. The only thing though is mine performs well under a load, like climbing hills or pulling a car around the yard.

 

You should still check the fuel pressure so you can rule that out.

 

I will. I'll check it this weekend.

 

If your fuel pressure is within specs, and all other troubleshooting proves nothing, consider your upstream Oxygen Sensor (O2S) as being defective.

I had a similar problem several years ago so I changed my upstream O2S and it fixed it.

O2S's are only good for about 120,000-150,000 miles. If your O2S's have never been changed and you have the mileages stated, it might be a good idea to replace them. Use NTK Oxygen Sensors. They were the factory sensors when your Jeep was built. NTK part numbers: Upstream (before Cat) 23151, Downstream (after Cat) 23099. These are exact fit.

I do not recommend Bosch O2S's.

Rockauto has the cheapest prices on O2S's.

However...If your fuel pressure is not in spec, like in Jeepin'Hubb's post, I recommend installing a Bosch or Carter (cheaper) fuel pump module. I do not recommend Airtex fuel pump modules.

 

Is there any specific tool needed to check the fuel pressure besides the fuel pressure tester itself, like special adapter?

Also why do you not recommend Bosch O2's? I check with carquest on getting O2's and that's all they have are Bosch O2's. I was planning on changing mine out bc I have 211k on the jeep and they are probably due lol