Hi I have a 99 xj sport that runs worse every time I start it?
It has always had this miss I couldn't figure out it surges on the highway and now just runs terrible?
My attempt to get it reliable and back on the road I have replaced the fuel pump cleaned the fuel line and rail it has new 4 hole injectors I have replaced every sensor including coolant temp and both O2's a new cat plugs leads dizzy the coil twice and crank and cam sensors it should run perfectly?
But no it has just gotten rougher I just checked the manifold gasket by spraying carb cleaner to see if it would skip and rev a bit But no difference Finally I am lead to think it must be a crack in the exhaust manifold as it is over fueling and has black smoke ?
When I was doing the spray test I couldn't hear any exhaust leak I am sorta running out of ideas?
I am going to change the manifold gasket and while it is apart I am going to fit extractors just incase it is the exhaust manifold I really don't know what else to do.
Any ideas?

 

I would apply a vacuum gauge and check the compression

 

Agree. And don't pull the manifold yet.

 

Ok thanks what pressure should i be looking at on a vac gauge off the manifold? as for the compression test? if it had low compression on a cylinder ie bad rings or valves it would smoke Blue and use oil it does not do that it is Black sooty fine smoke looks like it is over fueling ?

 

Any OBDII codes?

See if you enter closed loop. Test TPS and MAP (circuit could be bad). Got the service manual?

Check fuel pressure.

Check CPS/CKS sync.

Check the operation of the injectors and oxygen sensors. What do you have for testing equipment?

 

Could also be the PCM. Solder joints on the main connectors break, coil and injector drivers go bad.

Test test test.

 

codes?

 

I have tried 3 code readers and No Codes?

 

This might be dumb question of the day ... But you gotta think of everything when dealing with a XJ For the life of me I cant get it to run smooth I have replaced everything some twice .. REVELATION a Light Bulb Moment! Last time I had the throttle body off the gasket **** itself Not having any gasket paper I made one out of cardboard it was thick cardboard box cardboard you know with internal ribs I tightened it down good but are now thinking that the cardboard might of shrunk with engine heat allowing air in and making it run more ****house every time I drove it? Once you gotta love country towns I have to order some gasket paper off ebay and wait another week But this might be the $6.99 Fix ..... Fingers Crossed

 

Can spray a little carb cleaner round the base to see if your idle changes.

 

Couple thoughts

Do check the compression. A burnt/ bent/ sticking valve will not cause blue smoke or cause it to use oil as you mentioned.

You mentioned"new" injectors. Is this new like in fresh from China or rebuilt OEM.
Another thought.. you said no codes but when you look at the live data is the vehicle trying to go richer or trying to go leaner. Might help you figure out if it's a vacuum leak affecting all the cylinders or one rich cylinder that's causing the rich exhaust.

 

How many miles are on this engine??

As others mentioned, it's time for a compression test. Not that difficult on the 4.0 liter engine. The compression spec for this engine is 120-150 psi with no more than a 30 psi variation between cylinders. Start there and report back your exact compression results on all cylinders.

 

You didn’t list it, have you tried thoroughly cleaning your throttle body and IAC? Gunked up passages could easily make it run rough and rich. Won’t cost you anything and can eliminate a couple possibilities.

 

Guys I think I might of found the issue
Firstly tjwalker it has only 240.000 klm on the clock and poni the throttle body is clean with new sensors
I was changing the throttle body gasket I had a cardboard one on I made I thought it might be leaking and was I think when I noticed the butterfly did not snap shut it slowed down at the last bit and of you give it a rev the rpm comes down slow?
There is about or mm of play in the shaft in and out up and down side to side Me thinks it is Buggered and letting air in and the pcm is over fueling
As hot air is less dense than cold air when it gets to temp it sucks more air Anyway I managed to get a throttle body of a guy on a Australian FB Group for $ So I just have to wait on the post and see what happens

 

fixed it was the throttle body