Help!

The performance of my x-type is gone down pretty dramatically, my mileage has gone from 24.5 to 21mpg (US) and my Dynolicious App gives me tops 150hp.

Here is what I have tried:

-Cleaned MAF Sensor
-Cleaned Air Temp Sensor
-Removed K&N Filter and replaced it with new standard filter (in case it was oiling the MAF)
-Replaced Fuel Filter
-Used a can of SeaFoam in the gas tank
-Used SeaFoam deep creep through the air intake

All to no avail. I'm thinking about replacing the O2 or MAF sensors, but that's pretty expensive or cumbersome and I show no codes.

I'm absolutely at a loss about what to do... The car has 84k miles. Sparkplugs are less than 30k miles old. No hissing or vacuum leaks.

Car starts and idles just fine, but has no power. Exhaust smells too much of gas, so it's clearly a fuel/air mix issue. I just don't know where from.

Any ideas? Need some out of the box thinking here, guys...

Thanks in advance!!

cs

 

Are you running premium gasoline? Have you changed where you purchased your fuel recently? You're not using the new E15 gas are you?

 

Yes, 92 or 93, have changed gas stations a couple of times... no difference.

 

Tire pressure good? Low PSI makes you feel like you're driving through sand.

 

When you say the performance has gone down just what do you mean? Does the car misfire? Does it run or idle rough? Is the check engine light on? Has the mileage gone down suddenly or has it been since winter started? Have your driving patterns changed recently? If you detail the issue you are having better the chances of finding a resolution to your problem is better. Really, 21.5MPG in winter in Minnesota might not be that bad. Mine is about that in about 70/30 mix of city/freeway and my car runs fine.

 

Not all brands of spark plugs are created equal.

What is the brand of plugs in the car now, the ones with 30,000 miles on them?

If they are worn out or the wrong ones, that could easily explain the lack of power, poor mileage, and - do to poor combustion - the rich gassy exhaust scent.

There are many discussions throughout the forum, in all the different car models, about the "best" plugs, and the "best heat range". Personally, I think the factory specified plug is the best one.

Another thing it could be is a thermostat that is not working correctly. If your car never properly warms up, the computer will at the very least cause it to run rich and doggy.

My money is on the plugs.

//Be sure to change out the intake gaskets when you pull the manifold for the plug change, too!

 

Yes, the performance has gone down quite suddenly. I've had this car for 5 years and while the mileage goes down a bit, it's never been this bad.

It's really obvious, the kind of thing where hills that I used to climb in 5th gear now I need to downshift to 4th...

No misfire, good idling, no check engine light...

As I said... a mistery!!!

 

Those are all good thoughrs, Bruce, thank you... I don't remember what the spark plug brand is... but why would performance have dropped so suddenly? Can spark plugs go bad in 30,000 miles?

Temperature seems good.

 

Mechanical failures usually fall into one of two categories: 1) Sudden, catastrophic failure, or 2) a gradual decline due to wear until a part exceeds the minimum required for it to function properly. I think you might be at category #2; your plugs simply reached the end of their optimum useful life. "Optimum" is the keyword, thus the performance issues.

Yes, plugs can fail in 30,000 miles, but I am guessing yours simply wore out - for whatever reason. (Heck, I have a lawnmower that needs a new spark plug every 10 hours!)

As to your statement "Temperature seems good", read this product description about the temp gauge. Although it refers to different models of Jaguars, I suspect our X-Types may have the same issue as my temp gauge always sits dead-center in the middle, no matter how I drive the car.

Plugs and a thermostat are both inexpensive items. There are quite a number of "How To" here in the forum on how to change them out. Forum member daxter1987 seems to have one of the best DIY's on changing out the upper radiator hose. His instructions get you right there to the thermostat.

Best of luck, and keep us apprised on how it all shakes out.

 

The misses had a similar issue with her car. Sudden loss of power. We had it in the garage a few times, and told they couldn't find anything wrong. Even after a having it serviced and costing me a couple of hundred quid.
Seems that mechanics these days don't like doing the simple things these days. When I got some time off work, I replaced the plugs and HT leads. And the car is back to running how it should be. On inspection of the HT leads, they were all broken and not making contact. For the sake of elimination at least it worth trying, and will only cost you a few quid. Hope all works out for you.

 

Thanks all for your replies. I "think" I might have found the issue, which was on the MAF. The K&N filter was totally over-oiled and it wasn't enough to clean the sensor itself, I had to wipe out the whole intake and replace the filter.
It feels better now, but I'll know for sure as soon as I finish this tank of gas and can calculate the mileage.