My miles per gallon keep droping. After resetting the computers max mpg I have seen is 18.2 but it keeps droping and is at 16.4 right now. What worries me other than having to refuel so often is that im driving super soft purposly to conserve fuel but still. This making a big hole in my pocket. What can I do??? There is no check engine light codes. Car idles at 700rpm while on drive and a bit higher in neutral. I have only removed the second pair of cats. But the gas problem comes from before removing them. Sometimes I can smell what seems like fuel fumes in the cabin more in the trunk but there is no leaks. To be honest it seems to me like im not even getting the milage the trip computer shows. Im fueling $20 every other day. Taking the same trips I do on my toyota fj cruiser wich I put $20 every four or 5 days. I dont know where to start looking on thisone. My guess is that something with the fumes I can sometimes smell has to do with evaporative system but again dont know where to start cheking. Help

 

What kind of driving is this? If mostly city/traffic driving, 16 mpg isn't all that bad, IMHO. Mine gets 12-14 mpg in city drving.

If your getting 16 mpg on a steady speed highway trip, something is wrong indeed. It should be well into the 20s.

Anyhow.....

The "could be" list is long.

You might consider getting a scan tool that displays live data (as opposed to a simple code reader) so you can observe what the management system is doing. Having no codes on these cas doesn't mean much, as they tend to be very reluctant to set a code at all.

There IS one very easy-to-fix possibility. Does your temp gauge read "N" for normal? Or does is stay down towards the cold side of the scale? If the engine stays cold the system will over-fuel. Common problem; replacing the thermostat fixes it in nearly all cases.

Next, remove the exhaust manifold heat shield and check the manifolds for cracks. If cracked there will be outside air drawn into the exhaust. This tricks the computer into adding more fuel. These cracks usually don't produce an exhaust leak noise...so don;t be fooled. You have to remove the cover and actually look.

If you're in the mood for an inexpensive guess, replace the coolant temp sensor. If it gives a cold signal at all times, the system will over-fuel.

Others will chime in.

Cheers
DD

 

Doug, the temp gauge is not exactly in the middle, but almost there.

What is the way to check the coolant sensor with a voltmeter? For example after driving and engine being at full operating temp what should I set on the voltmeter and what should ir read?

 

I'll try to find the specs


DD

 

I had a brake caliper hanging up on me. Cost me 2 mpg.

 

Does the station pump kick itself off occasionally while fueling up? There is a 'relief valve' (Rochester Valve) which sits atop the fuel tank that relieves pressure buildup in the tank. When that valve is faulty, there is no way for adequate air to escape the tank and pressure builds causing the fuel pump to work harder. The fuel flow rate starts to decrease creating a leaner condition and the computer will try to compensate by increasing fuel flow (riching). That pressure buildup in the tank also results in the smell of fuel. A poster here has a writeup on his experience leading to a Rochester valve replacement, and he located a suitable AC Delco replacement (ac delco 214552) for about $25 that was a perfect match and solved his problem.

https://www.jaguarforums.com/forum/x...ntinued-81248/

Also, sometimes the most obvious mileage culprit gets overlooked - faulty O2 sensors.

 

for me it was the rochester valve, take a look at my post as mentioned above.

 

thank you i will look at the post. altho i dont have the pump kicking when fueling. i do have the smell

 

I seem to be having Rochester Valve issues.
Where is the thing? i got info thats its on the top of the gas tank, or under the floor? i ordered the new valve but im gonna need to find the old one first

 

Found it on left side. ha!

 

If one suspects one's Rochester valve, can one drive around with a loosened petrol cap? That would be a simple test, would it not?
I might even try it for the hell of it, to see if my car uses less fuel.

 

That's what I'm doing.