Topic: Why is my Jeep running rough?

[bustedknee]

I bought a 2000 Wrangler, used, last summer (Virginia).  2.5L Engine(EPE)/5Spd M/T AS72(DDQ)  Stock except for the tires (to the best of my knowledge).

The previous owner had just done "several things" to it.  He was a little sheepish about this but did say he replaced the plugs as well as plug wires.

It did run a little rough, especially when under a load.  It didn't really miss, but almost.

I added a can of Heet to the next couple of tanks of gas and performance improved immensely.  Since I lived in Alaska for 33 years I am familiar with water (condensation) in the tank, so I figured that was it and I had solved the problem.

After the next tank of fuel without Heet I noticed it ran just a tiny bit rough when under a load.  So I added another can of heat and it smoothed right out.  It ran as smooth as a Singer sewing machine!
I looked up Heet on the Internet and found that it will slightly boost the octane of a tank of gas.

After the price of gas went down I tried a tank of high octane fuel.  Again, it ran as smooth as a Singer sewing machine!  My milage jumped from 17-18 MPG to 20-21 MPG!


I'm not much of a mechanic so I can only speculate on this.  Did someone do a tuneup on this vehicle while it had a tank of Hi-test and now it prefers Hi-test?  Or could they have done something else?

And my second question:  Will using hi-test hurt my little engine in any way?

[Jeffy]

I'd check to see if it has a JET Stage II Chip or something.

Unless he increased the compression or changed the PCM somehow, it shouldn't be running rough with Regular.  Maybe had carbon build up?  How do the plugs look?  I'd maybe run a can of Seafoam though the engine.

[bustedknee]

Without looking at the Jeep it sure sounds like the "Chip" to me. 

I'll investigate and get back to the forum.

Thanks

[bustedknee]

I looked around under the hood and I don't know what I'm even looking for. 

From the website for the chip it looked like there was a plug somewhere on the left side of the engine?

Nope.

On the firewall.

Still researching...

[bustedknee]

Okay, it does NOT have an aftermarket chip.

I was sure that was it from the symptoms.

I took it in for service and the dealers says everything is fine except dirty injector...  Which he "cleaned". 

Since my radio was deprogremmed I suspect they did a reset as well.  Hell I could have done that.

Hmmmm.

[bustedknee]

Final Update:

Four days after the service dept gave my Jeep a clean bill of health the engine light came on.

I took it back in and they said the code indicated an "EVAP Sensor" problem.  They found a cracked hose and replaced it.

They also said this would not cause my complaint.

However,

The problem is now gone.  My Fo-Bang-Ah is runing as smooth as silk.