Engine Mileage = Bad fuel economy?

[LJS30]

Lately I've been getting really poor fuel economy from my Mark 7. My computer says I'm getting about 18 mpg which has been steadily going down for some time now. My tire pressure is good and the 5.0HO just had a tuneup in order to pass California smog. Now, the engine does have over 200,000 miles. So could this possibly be the issue?

[HRLMVII]

have you noticed any change in engine speed or load while driving?

have you been having any problems with your transmission?

and have you had an alignment done lately?

[LJS30]

have you noticed any change in engine speed or load while driving?

have you been having any problems with your transmission?

and have you had an alignment done lately?

Transmission is good, rebuilt in fact. Alignment was done several months ago also. My engine idles smooth with no misses also. I'm stumped.

[90LSC]

Crappy gas.

[HRLMVII]

Have you tried using a can of sea-foam, http://www.lincolnsonline.com/tech/00151.html the stuff works awesome,

also try a can of RESTORE - its at any major autoparts store

[gadget73]

How much vacuum does the motor pull at idle? Thats a good indication of overall engine conditon. The higher the better, but you need at least 17" to run right. 18-19" will give good fuel economy, if you can get better than 19" at idle the engine is in good shape. When was your last tune-up? How old are the oxy sensors? They're only good about 60k miles, so if yours are original I'd seriously consider replacing them. The catalytic converters might also be starting to clog by this point in time, which will cost you power and fuel economy. Have you changed the differential fluid? Are any of the brakes hanging? Rear axle ever been rebuilt? What about the front wheel bearings, how old are those and when was the last time they were re-packed?

I'd look at that stuff before jumping straight to worn out engine. You'd also likely get better results out of a set of spark plugs than a mechanic in a bottle.

[LJS30]

How much vacuum does the motor pull at idle? Thats a good indication of overall engine conditon. The higher the better, but you need at least 17" to run right. 18-19" will give good fuel economy, if you can get better than 19" at idle the engine is in good shape. When was your last tune-up? How old are the oxy sensors? They're only good about 60k miles, so if yours are original I'd seriously consider replacing them. The catalytic converters might also be starting to clog by this point in time, which will cost you power and fuel economy. Have you changed the differential fluid? Are any of the brakes hanging? Rear axle ever been rebuilt? What about the front wheel bearings, how old are those and when was the last time they were re-packed?

I'd look at that stuff before jumping straight to worn out engine. You'd also likely get better results out of a set of spark plugs than a mechanic in a bottle.

I'm not really sure what the vacuum is at idle. I will get that checked for sure. As for the oxygen sensors, I had those changed over a year ago due to an upcoming smog test. My last tuneup was in June because I had to get it ready to pass California emissions, which as you know are very stringent. I've had two of the cats changed when I had my complete exhaust rebuilt. However the two cats up front, where the header collector would be have not been changed. Brakes were completely done in June, with wheel bearings changed out also. Rear axle has never been touched but the fluid was changed in June also. Perhaps catalytic convertor?

[Tony T]

My 2cents, most gas now contains up to 10% ethanal, (at least in NY) with out really checking it seems even my Lebaron gets a lot less mileage.

[gadget73]

Could be the front converters are somewhat restricted. The ethanol will play a part too, no doubt. If you really want to know the internal condition of the motor, a basic vacuum check at idle will be useful. That will also show vacuum leaks, and those definitely mess with fuel economy. Beyond that, a leakdown test wouldn't be a bad idea, and you might want to check the slack in the timing chain. The most accurate way to do this is to take the cover off, but you can get a pretty good idea if its sloppy or not with some careful observation.

Remove the distributor cap. Put a long ratchet, breaker bar, etc on the crank pulley with a 15/16" socket. "Rock" the crankshaft back and forth and observe how far you have to turn the handle to get any movement out of the rotor. It should be very small, but if you can really notice the crankshaft moving independant of the rotor, the chain is pretty loose. Another place this sometimes shows up is at idle when checking the timing. With a sloppy chain, the timing mark will sometimes seem to dance around.

If you are going to have someone pull the timing cover to check the chain, just have it replaced. They're cheap, and once the timing cover is off, its maybe a half hour of work to swap the chain out. The fun part is getting at the cover. Ford in their infinite wisdon mounted every stinkin accessory to the timing cover, and it requires removal of all the accessory brackets off the front of the motor. Its a real blast to do.

[LJS30]

Could be the front converters are somewhat restricted. The ethanol will play a part too, no doubt. If you really want to know the internal condition of the motor, a basic vacuum check at idle will be useful. That will also show vacuum leaks, and those definitely mess with fuel economy. Beyond that, a leakdown test wouldn't be a bad idea, and you might want to check the slack in the timing chain. The most accurate way to do this is to take the cover off, but you can get a pretty good idea if its sloppy or not with some careful observation.

Remove the distributor cap. Put a long ratchet, breaker bar, etc on the crank pulley with a 15/16" socket. "Rock" the crankshaft back and forth and observe how far you have to turn the handle to get any movement out of the rotor. It should be very small, but if you can really notice the crankshaft moving independant of the rotor, the chain is pretty loose. Another place this sometimes shows up is at idle when checking the timing. With a sloppy chain, the timing mark will sometimes seem to dance around.

If you are going to have someone pull the timing cover to check the chain, just have it replaced. They're cheap, and once the timing cover is off, its maybe a half hour of work to swap the chain out. The fun part is getting at the cover. Ford in their infinite wisdon mounted every stinkin accessory to the timing cover, and it requires removal of all the accessory brackets off the front of the motor. Its a real blast to do.

Very good points. Thanks.