Have 93 xj 4.0 manual having trouble accelerating and getting up to 55. Put in new air filter,fuel filter. Starts fine idles fine. No power up hill

 

Hey, Phil, welcome!

This should really be in XJ OEM Tech. This area is more for general chit-chat, rather than specific technical problems.

I'll flag your post, and a mod will probably move it, so if it disappears, that's why. No worries - it will still be there, just moved.

How's your fuel pressure? That would be the first place I'd look for that problem. You'll need a gauge to be sure. IIRC the spec on yours is 39 psi, but you should verify that.

Cruiser54's tips are a good place to start with general maintenance.

 

agree sounds like a fuel problem. fuel filter been changed?

 

Yup.

 

oops, guess reading isn't my strong suite...lol, plugged converter?

 

Three reasons come to mind:

The first is having a clogged fuel filter. Since you already addressed this one having changed it.. It is probably not it. I think it would be wise to verify having the correct fuel psi with a gauge immediately after a prime with the engine off, during idle, and while under a load when driving.

The next thing I think of is having low compression. This is very high on the list if the fueling checks out okay. Doing a compression check is easy to do, and is a wise thing to do if your Jeep is sluggish and having difficulty with acceleration.

The third thing I think of is the intake. A very clogged air filter also has been known to cause sluggish acceleration to occur. This is something you have already done though. It is difficult to restrict air intake in many other ways.

Depending on who you ask, the above three seem to ussually be considered the top three reasons for having very sluggish acceleration.

I thought of a fourth reason. An exhaust restriction can cause the same sluggish acceleration too. The catalytic converter and the muffler are the two areas where an exhaust system can become clogged.

Spark plugs, oxygen sensors, and fuel injectors are all worth bringing up to mention.

It could be a combination of different reasons contributing together to cause sluggish acceleration..

 

Agree that fuel pressure must be verified before looking to more complex possibilities. It is what any technician worth their salt would have at the very top of their list for testing if your XJ was in their shop.

For your vintage XJ, you should have approximately 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the fuel pressure should jump to approximately 39 psi.

Also, be sure that there is no raw fuel in the vacuum line leading to the fuel pressure regulator. If so, that indicates a ruptured diaphragm in the regulator which necessitates replacement of the FPR.

A fuel pressure gauge can be rented inexpensively from many parts stores if you don't have access to one; call around for availability. Testing takes just a few minutes. It screws into the "schrader valve" on the fuel rail, looks like the valve stem on a bike tire.

Good luck and keep us updated!

 

I had that problem with a Nissan Hard body, It was a weak coil . It ran fine up to 3000 rpm and then poof it wouldn't get out of it's own way. Just a thought.