Hello all...

The past few days I have been having an ever-worsening problem with my '98 XJ 4.0L...

From a cold-start, it will fire right up in a ½ second, but once it has warmed up to temp, it will idle rough and stumble trying to catch itself. I can also start to smell un-burnt fuel from the exhaust as it it sitting there trying to catch itself, like it is running really rich or something.

More recently, tonight on my way home, it has started just randomly sputtering and popping during acceleration and cruising at speed. It will start to catch, but I have to lay-off of the throttle and work it on and off to get it catch itself again and accelerate back up to speed.

It also seems to lack power when holding the throttle constant while cruising at speed, like its choking itself out.

I have pulled two plugs, cylinder 3 & 6, to check their condition. Pic is below, but the look to be wearing normally to me. Light grey coating on the electrode and end.

I am going to test the TPS voltage to make sure it is reading correctly. I also have no CEL lit. I am pretty good with electrical, so any testing involved will be pretty simple for me.

I have read a few threads from here and another forum, but everyone's suggestions and solutions are all over the place. From the TPS to the CPS, Cat Converter, Injectors, Fuel Pressure, etc...

As far as injectors go, I have the 703 4-hole ones in my 4.0 currently, and have had them for over 1½ years now... I had to replace my cat-converter about a 1½ years ago too, along with an O2 sensor too...

So, any suggestions on where to start, or another diagnosis to try?

Thanks in advance for all of the info and such from everyone... I've have found solutions to many issues with my XJ from you all before, so hopefully I will once again!

 

Checked the gaps on the two plugs... One is at .042 and the other at .045...

I set them all to .035 when I installed them...

 

Ok, TPS test...

Feed Voltage = 5.7
Idle Voltage = 1.12
WOT Voltage = 4.58

Ramping up and down the throttle range read smooth... No spikes or dropouts...

Here is a pic of the throttle body... Pretty clean compared to others that I've seen cause problems...

 

Fuel pump may be going. You should definitely check pressure. If its dropping during the sputter that would be my guess. Mine was acting similarly when the pump was dying.