I have a 98 xj classic and the engine is back firing in the intake and really sluggish at take off every now and again more more frequent here lately.
I have replaced the following:
Fuel pump with new screen,
plugs, wires, cap, and button,
checked all sensors,
not getting any codes at all.

Problem is still there, i had a 96 xj come thru the shop that had similar problems was upstream o2 sensor. But i want a few ideas before i spend 100 bill on a oem sensor. Any suggestions?[/font]

 

I had the same problem with my '98, and it ended up being the upstream O2 sensor. Unplug the sensor and drive around. If the problem goes away, replace the sensor. Mine was instantly better when I unplugged it.

Also, does it stop running rough when you give it full throttle?

 

When I give it full throttle it'll just back pop a couple times then take off like a bat out of hell

 

Check your exhaust manifold for cracks. Your symptoms sound like mine. It is the o2 sensor but only because it can't get a proper reading when the exhaust leaks out before the o2. The tiniest crack will do it and you won't even get a cel

 

No cracks already replaced the manifold

 

Really sounds like ignition if the fuel pressure is good, you did check it, right? What does your scan tool say the TPS is doing?

 

What I know is mostly Renix, pre 91. Floor-boarded, (or past 70/80% throttle) it will ignore most of the sensors and run on default settings in the puter'.

Mine popped back out the intake for at least a year before I found a wire shorting to ground. Yes, it would "launch" floor-boarded LOnger story shorter...Might have been the temp sensor (sender?) Maybe my one 02 sensor 5v feed wire. Yours is different, but still if wires to ether of those were shorted to ground, or shorting in the harness the puter might be getting bad info.

I think without a temp sender or an 02 sensor it should function OK, just not optimum. In your shoes I might unplug some stuff and triple check the wiring for anything chaffed or shorting. With no signal the computer should make it at least work OK.

This problem, backfiring out the intake comes up regularly, and normally we don't see a solution, the thread just stops. It's said that happen when it's extra lean, which a temp sender might be able to cause. Hope to see a solved post someday!

 

No codes on the scan tool to and all others working like they should. Ended up changing front oxygen sensor and its fixed the problem. Thanks for all the help

 

Cool! Much thanks from all for getting back with your solution, and glad to hear you got it!

 

You bet. The guys on this forum helped me diagnose mine, so I can only pay it forward.

 

Same here! Glad you got it, xjclassic!

 

my 91 was doing same thing ended up being a coolant temp sensor

 

I'm not positive, but I'm pretty sure it was a coolant temp sensor wire grounding causing my intake backfire with throttle. Was "pre forum", I just fixed the wires without knowing exactly which one it waz.