Might be time to bite the bullet and take it in to the dealership for a diagnosis. The wear you're putting on the car in the interim may end up costing you more than paying a professional mechanic to identify the source of your issue.

 

Matt,

The car has been to the dealer, AAMCO and neither could find a problem.

Today I replaced the fuel filter (10 minute job!!) and the car feels a little lighter (maybe just my imagination) but still not quite right. The filter I removed was Jaguar labeled so it might have been original.

The only thing that I have left to change is the spark plugs and associated gaskets.

 

Matt,

The car has been to the dealer, AAMCO and neither could find a problem.

Today I replaced the fuel filter (10 minute job!!) and the car feels a little lighter (maybe just my imagination) but still not quite right. The filter I removed was Jaguar labeled so it might have been original.

The only thing that I have left to change is the spark plugs and associated gaskets.

 

Do the spark plugs!!!!! Mine were original and I restored most of my factory power with a new fuel filter, new gaskets, new plugs. I ended up getting 2mpg better after I did my plugs too just because nobody had dealt with them yet.

 

I will change the spark-plugs as soon as I can. My
Fuel consumption is just horrible. At this point the 95 XJS gives me the best, followed by the 74 E and the X is a very distant 3rd!!!. How the hell does a 2004 V6 drink so much fuel that its MPG is worse than a 74 V12??

If its not the spark plugs I don't know where else to look. I am pretty sure my
Fuel consumption issue and my lack of power issue are one and the same. I have no check engine light

What are the correct or original plugs to use on this car? I heard Autolite somewhere?

Thanks for any help

 

Mark, the excessive fuel consumption is interesting. Good fuel economy is one of the more notable things about these cars. My 3.0 automatic gets about 28 miles per gallon on the highway, and about 20 to 22 in the city.

Hope you're able to diagnose the problem soon!

 

Spike, when you say you are getting horrible fuel mileage, can you tell us what you are getting and your driving patterns? A lot of short drives will really cause low fuel mileage or, maybe as low as 12MPG if you only travel a few miles each trip. I would think overall something in the 18-23 MPG range would be "normal" if you would typically get the car fully warmed up and have some kind of city/highway mix of miles in there and the car was in good tune. I know you have been battling that sluggishness issue for a while now. Hope you get to the bottom of that soon.

 

She performs and drinks more gas in stop and go city driving. In the freeway she's a dream. Obviously I understand this car is AWD and that stop and go driving drinks gas, specially in 110 Houston weather. It's just a bit hard to accept that a 1974 V12 car is getting better MPG under the same circumstances, both cars have A/C in full blast.


As soon as I can figure out what spark plugs to use, I will replace them along with the rubber gaskets.

 

At this point I am getting 12-14MPG with some highway driving. It's really terrible.

The sluggishness (specially out of first at stops) continues to randomly come and go. I am going to replace the spark plugs with Autolite double platinum a, but I see that the original plugs are supposed to last 100k miles. It looks like a pretty tough job.

 

Spike, new plugs is not that bad. The big thing is making sure you get the 2 bolts on the back side of the intake. Else it will feel like you have some other bolts that are still installed. But, once you do it, you will laugh at really how easy it is. The big tricks is not forgetting the 2 bolts (1 dead center, kinda on the underside of the intake and then one down near the elbow/bend on the underside of the intake) and then also make sure to disconnect the throttle body from the intake so you don't have to undo the coolant lines. After that, it is pretty simple. Probably a good time to do the IMT o-rings if you haven't done those in the last few years.

 

Thermo, thanks. I have been looking thru the archives and its definately do-able. My IMT o rings where one of the first things I did. Plugs is the only thing left that I can do.

It's so frustrating to not know what's going to happen when I press the accelerator. Sometimes she goes, light as a feather, sometimes she feels like a tractor and just kind of sits there for a second.