poor mileage, no other symptoms

[dlb]

a while back i disconnected the vac advance and was running at 13* BTDC and was getting about the usual mileage, 30+ mpg. in the last few months though it has fallen to consistently around 25 mpg. i'm driving the exact same mix of city/hwy and there are no noticeable changes in the cars performance. last year i had a similar experience except that the car would idle poorly while cold. i looked and found the choke was stuck but no such symptom this time around. i checked anyway and found the choke to be operating fine.

i have since cleaned the air filter, checked tire pressure, swapped dizzy's with the parts car, set the timing to stock 5* BTDC (no pinging this time around), and hooked up the vac advance again, but all this has had no effect on the mileage. i've currently got my 185/70R14 winter tires on but i've taken the tire size into account when calculating mileage. this started before i put them on and they're not super aggressive tires anyway so i have ruled out increased rolling resistance.

i can't remember when i last changed the fuel filter but it has not been acting fuel starved, which i've usually found is the way an old fuel filter presents. i should probably swap it anyway since it's only $5.

thoughts?

[takza]

* could be the tires?

* colder weather?

* winter gas?

* diaphram on the carb...the one that leaks?

* front toe alignment?

* still might be a good idea to use some carb cleaner and then some light oil to free up the coke and be sure that it is fully open when warm?

[dlb]

i should add that i have made no other changes to the car recently besides the ones i already mentioned (winter tires, dizzy swap + vac advance hooked up), and that i've still got the weber on the car. this will be the third winter i've had the weber and never had any cold weather mileage issues in the past.

had the alignment done earlier this year. i'll clean the choke and check it when warm like you suggest, takza.

[Petros]

the fuel filter change will have no affect, save your money unless it needs a new filter. check your brakes from a draging caliper, this happens more than most realize, affect economy noticably.

[dlb]

takza, i owe you a beer--'twas the choke not being fully open when warmed up! just three screws to adjust it and mileage is back to normal, huzzah!

[takza]

Easy fix!

Just redid the alignment on my Focus and found it was off quite a bit....seems to have improved mpg. I'll be rechecking every 6 months. Seems every time I check alignment on something...it is off. Way too easy to hit a pot hole or something.

Now using ADVANCED STRING THEORY:

https://tercel4wd.com/forums/viewtopic.php? ... 300#p45300

[dlb]

i was going to ask how you're digging the focus so far. is it ready for winter? i'm not sure if you get snow at the plateau.

[takza]

All I can say is...it's not a winter car....though it's not a rear wheel drive pickup or wagon. Other wise...doing OK.

[dlb]

well, the choke adjustment has helped but not as much as i hoped or imagined it would. just got 26 mpg on the last tank. i was chatting with a friend about this though and he mentioned a plugged exhaust could be affect mileage. as soon as he said this i remembered that a few months ago, right around when my mileage became poor, i noticed my exhaust sounding kind of funny on start-up. like it had a hole in it somewhere, but i looked and couldn't find any. the sound mostly improves after a few minutes of driving. i had a new muffler (and pipe? not sure) put on 1-2 years ago.

i guess my questions about this are: are newer pipes/mufflers as prone to buildup as old ones? are there normally other symptoms involved? how can i check to see if the exhaust is in fact plugged?

*edit* i should add that i do not have a catalytic converter.

[Highlander]

Dave- Do you have an associated loss of power? A plugged cat will make the engine work harder and eventually can stall it out. I don't know of a quiet way to test the exhaust for blockage-but if you crack the connection into the cat it'll free up the exhaust restriction (if any) and have your Butt-dyno tell you if its got more ooomph or not. Not very scientific, and not very repeatable or consistent, so YMMV.
For many years I thought that my cars did great not having the cat block up on me only to find out that they all had had the catalyst punched out -they still passed emissions, but it would have been easier had the cat been functioning.

[dlb]

sorry highlander, i just edited my post to say that i do not have a cat in the mix. just a pipe and muffler!

just finished googling this. didn't find a lot of useful info but someone did mention that "a restricted exhaust will cause a drop in engine vac." this is interesting because i hooked my vac advance up again and noticed it was advancing 1-2* less than in the past, and that i was not having the good ol' predetonation problem this time. this seems to point to a partially clogged exhaust, no?

[4wdchico]

Got it that you do not have a cat now. But if it did have a cat at some time in the past the innards could have passed downstream and partially blocked the pipe or muffler. The vac gauge test with the should show a difference with the after cat piping connected/disconnected if you have a partial blockage.

That or test it by running it wide open up a known grad that you have powered up before. A car with a partial exhaust blockage will fall on it's face at some point and not reach full RPMs and power.

[dlb]

no, i can't say there's been any loss of power up steep hills or anywhere at all for that matter, and the pipe and muffler were replaced along with the cat. it's been driving fine and i wouldn't know there was a problem if i wasn't obsessive about mileage. i will scour my exhaust tomorrow though because the strange exhaust sound does seem to coincide with the poor mileage. that's the only concurrent symptom i have come across so far.

[dlb]

peter, what would you do for a dragginc caliper? spray some PB blaster around the caliper piston maybe? i checked and it feels like my driver side might be dragging a little. passenger side was fine and i checked both rears as well just to make sure the parking brake wasn't dragging but they spun much more freely than the front.

[Petros]

You have to replace the caliper, or the flex hose. Either the flex hose is internally falling apart and it acts like a one way valve (not releasing the pressure) or the caliper is full of corrosion and the piston does not retract all the way. What happens is when you step on the brakes the pads do not retract and drag on the rotor. Usually if the brakes have not been applied for a while it will slowly retract so you would not know by just turning them. You have to have someone step on the brakes hard, with the suspect wheel in the air, and you see if it rotates freely before and right after the brake application. You also get accelerated pad wear, so if the pads are wearing uneven it is also a good indication of a caliper hanging up.

Realize that both the rear and front brakes should drag a little, just so you can hear it. If it did not do that there would be too much pedal travel. But it should not be too much drag, just a little.