I have replaced spark plugs, coils and fuel filter. I am use high octane fuel and adding injector and fuel system cleaner to my gas. My 2004 ski 4.2 liter is skipping when I get up to steady operating speed . It may be skipping before that but I don't notice it. Can definitely feel it when I get up to speed. 55, 65, 75 mph etc. Anyone have suggestions. Thanks.

 

Oldelance,

I suspect you're referring to an engine misfire at highway speeds. Is the misfire intermittent or consistent and/or related to hot/cold or just speed? We could do with a bit more information, such as the car details, Model Year, model (XK8 or XKR), mileage, service history etc.

How you plugged in a OBD reader, as the DTC codes will quickly point out the main culprits - fuel or spark. Otherwise you're throwing parts at a problem and it could get expensive. If it's not a misfire or a stall, it could be a loss of power which could be a sign of old Auto Transmission Fluid (ATF) as this causes problems such as you're describing when hot. At the age of our X100s, the ATF should have been changed once at least by now. Check your service history.

As you changed the spark plugs, coils and fuel filter, I would check fuel pressure (available over OBD on some models) during a run when you have the problem. May be a drop in pressure is a sign of a fuel pump going bad (XKRs also have 2 fuel pumps). Also if the problem is on a cold start, you can check the wiring looms to individual cylinders. On an old 1972 Triumph I used an old trick of spraying fine water over the wiring loom above the engine to see if I had sparks which is a sign of an electrical fault in the wiring. Not sure that's applicable or even safe on this motor.

Anyway give us as much info as you can, for us to help.

 

Info for you.

 

It's a 2004 jaguar xk8 4.2 liter 150,000 miles. Just changed the transmission fluid and filter. Have completley gone over the car and have caught up on all maint. Just had to replace the yoke and seal on the differential. It's just a slight skip at cruising speed. No loss of power and other than that the car runs great. Someone mentioned that I may need to replace the injectors.

 

Thanks for that.

With all the work you’ve done, it does lean towards a fuel problem.

Get any half decent garage to read the DTC codes from the OBD port and post them here. Otherwise you’ll be guessing which cylinder has the problem. Expensive to fix them all when you’re not sure of the problem.

 

Thanks for help. One other thing . My check engine light come on sporadically, and when it does I can definitely feel the skip
.

 

Well, the P020x DTCs are for injector problems and do cause a Check Engine Light, but...

as yours is intermittent, and the car should go into restricted performance mode - limited to 3000 RPM, maybe it’ll be a P0300 Random misfire DTC which leads us back to fuel delivery (ie pump) or an electrical fault to the ignition (ie module/wiring for spark).

Really need the DTCs to narrow it down.

 

Thank You I'll definitely get it check it out and keep you informed.