I just rebuilt the 4.0 in my 88 XJ.. I replaced every wear item I could think of including all new sensors ,with the exception of rings and valves (that were still in good shape).. Engine now runs with plenty power but when I'm cruising with no load like downhill it will sputter bad... Any ideas? I have a new fuel filter & fuel pressure regulator but old injectors & fuel pump.. I'm not sure if it did this prior to rebuild because it leaked oil too bad to drive so I just pulled it and rebuilt it..

 

Did you check the timing chain when you rebuilt it? When I did mine I checked and it had tons of play so I replaced it. Mine seems to be doing fine now so I'm guessing that was it.

Does the sputtering go away when you try to accelerate hard when it does it?

 

Probably something to do with fuel, all injectors working properly? Does it sputter while throttling or just when you let off to coast? timing correct? many things to check

 

Yes.. I replaced timing chain and made sure to install it correctly.. As per my Haynes manual ... It also seems to be running rich if that helps... I sprayed the injectors off with carb cleaner prior to reinstalling them.. I'm thinking about getting the fuel pressure checked...

 

Get that checked, run good under heavy throttle?

 

It does fine when revved up climbing hills on the highway and driving light to light in town .. It's just when cruising easy 65-70 mph on the highway...I think I'm gonna get my injectors and fuel pressure checked when I get some time... New fuel pump is only $40 on Rockauto.com so with 220k miles I might just change it anyways..

 

Check the vacuum line to your MAP sensor. It goes from the valve-cover side of the throttle body to the sensor on the firewall. Also, check to make sure all of your spark plug wires are snapped onto their respective posts.

 

Index your distributor per post 13 in the Mostly Renix Tips link in my signature before monkeying around with anything else.

 

Map sensor vacuum line is connected properly and when I put the plug wires on its habit to pull the rubber boot back and see the wire snap on before sliding the boot down..

 

See post 8...........

 

I found the problem.. The o-rings crapped out on my #4 injector... Pissing gas and sucking air causing it to run rich... Problem solved ... Thanks anyway for the suggestions..