(96 xj 4.0 i6 classic 6 inch lift 35 inch tires cold air intake aftermarket exhaust) so im in my 3 week of owning my jeep and something ive noticed is if i dont put the highest grade fuel (93) in my tank that my jeep will stall and die as if its not getting enough fuel in the system. So im questioning is this normal and are you supposed to put this fuel in our jeeps or is this concerning like i think?

 

Many people fall for the misconception that higher octane fuels are somehow better than the rest, and this is wrong. Don't fall for that.

Octane level is all about ping/knock/pre-deotonation resistance. There is zero use that a run-of-the-mill 4.0 I6 has for anything higher than regular (whatever "regular" happens to be at your altitude).

If your Jeep is having issues running on regular, something is wrong and needs to be addressed. Fuel pressure/fuel pump, fuel filter (most 96's and all earlier years have them), injectors, O2 sensors, cat, TPS, IAC....all of these things or more could be your culprit. Start diagnosing and eliminating possibilities.

 

Where would you recommend starting with diagnosis?

 

Replace the fuel filter. If problem still exists, check fuel pressure. Possibly may be time for a new fuel pump and pickup screen/sock after replacing the external filter.

Also may need a tuneup? How the the spark plugs look? Wires? Cap and rotor?

Start with the basics.

Yep. The 4.0 is a low compression engine and will not detonate 87 octane if timed correctly. No need to run any higher octane. Remember: The higher the octane, the SLOWER the fuel burns.

 

This.

 

All spark plugs and wires are new so ill try fuel filter and see how that works

 

Anything with electronic fuel injection and electronic ignition with low compression will run just find on regular fuel.

I had to bump up to mid grade when I was running my 85 carbureted 2.5L at 16-18 degrees spark advance to keep it from pinging. If you are getting ping on a fuel injected I6, you would have to have either really bad carbon buildup in the cylinders or something wrong with the ignition system.

 

Yeah running the wrong octane will cost you more and could hurt your mpgs a little bit also.If normal gas causes you to stall your either using a cheaper gas station with crappy gas or you got fuel system problems.

 

I run a tank of premium from shell once a month or every 6 weeks pretty much just for added cleaning power from their "V-power" I notice no difference in performance or MPGs as a result. But as part of a raise package I received from work I have a gas card with 400$ every month. If i didn't have that, I likely wouldn't spend the extra 15 bucks it takes to fill up (its a dollar more a gallon for premium by me) and just get a $4 bottle of STP injector cleaner. I advised a friend of mine to do the same thing, once a month or so to fill up with premium, and he claims that he gets noticeably better MPGs, ( GMC Terrain) But I think the bump in his economy has more to do with better driving habits because he just spent so much more on gas.

 

Unless your buying ethanol free gas that stuff does semi work as a fuel system cleaner since its alcohol,And most of your fuel system cleaners are alcohol based.

 

Cap and rotor been removed for a good visual inspection? Basics........

 

This should be engraved at the top of every page of every automotive forum on the Internet.

 

Heh. Please tell me where you can find 97 octane outside of an airport!


(Yes, I know it was a typo.)

 

Whoops.. 87 octane.. Been working two jobs lately and running on less sleep..

In South Dakota we have 87($2.17), 89($2.39) and 90/91 octane at the pumps. 91 ($2.89) is usually ethanol-free so of course I buy that for the yard-tools. doh.

 

And spark plug gap and torque. I'd then suspect the intake modification from factory could be the culprit.