Lousy fuel economy
 

Hi guys,

So, typically with my driving pattern (about 90% city, extremely short trips, cool weather) I get about 21 or 22 mpg. When I've driven a tank of mostly freeway miles, I can see up to 24 or 25 mpg. This consumption been fairly constant over 5 or 6 tanks. I always fill up at the same pump at the same station, so I am pretty confident about eliminating that as a variable.

These last two tanks, I've noticed my fuel economy get noticeably worse - like 19 mpg. This started about two or three weeks ago. The only thing I have personally changed since then has been my primary (inline) fuel filter. I've checked the hose clamps repeatedly for leaks and it seems to be just fine... unless maybe it's a really slow leak I am just not noticing.

I haven't checked tire pressures (but will) but I can't think of anything else, unless I am suddenly getting winterized fuel - but this late in the season?

Any other things I ought to explore?

Yikes... city driving is very, very hard on cars, especially if they are short trips where the engine doesn't get a chance to reach operating tempurature. Carbon build up may explain the fuel economy problem, perhaps? I would suggest a nice, long highway drive, or perhaps an italian tune-up. Don't be shocked if you see smoke belching out the back when you get up to speed.

Oh, don't I know it! I try to get it out onto an open stretch of road and just open it right up every week or two. I've been pretty consistent about that too, but I am mostly intrigued about why the drop in economy has been so sudden. My driving habit's really haven't changed, but maybe I just need to be driving it harder and more out of the city? Not sure.

I also should add - my short trip are generally a few miles of stop and go - but about 30 minutes worth of time. So by the time I reach my destination, the engine is actually up to operating temperature (and the oil is at the pressure I normally see when the motor is at operating temp, about 1.5 bar). That said, yeah - lots of short trips.

It could be the fuel formula has changed (ie adding 10% bio Diesel or something). I agree, too early for a change to Summer Fuel in BC.
I think goo has accumulated on your injectors and you need to dump some Diesel Injector Cleaner in the tank and do the "Italian Tuneup". Search the forum. Basically a fun Sunday Drive on hilly roads.
Then if the problem persist, look for fuel leaks, air constriction, injection problems ect.
Do the Italian tune up and check back. I have full confidence this forum forum will help you sort it out.

Tire preasure ?
Brakes hanging up
Transmission slipping
bad thermostat

JOHN

Valve adjustment and condition of air filter?

More pertinent information:

1) Valves were done ~ 5000 kilometres ago.
2) Air filter is new - only about 800 kilometres on it.
3) Tire pressure I will check today, I could be low.
4) Brakes don't seem to be hanging up any, but I'll check.
5) Tranny shifts exactly as it always has - no change there.
6) Tstat seems fine, the car operates at exactly the temp it always has (typically around 85 degrees in the city)

Right now I am guessing the most likely culprit is my tire pressure. There are really so many variables though. Perhaps my station's fuel supplier changed fuel on them? There has been a recent cold snap - maybe that has had some effect in combination with my short trips?

I will let you guys know what I find when I check out my tires and we'll see what effect that has if any.

19 is not a big dif in economy vs 21... fuel mix change at the pump could explain it. as could the tire pressure. alignment, brakes. the miles on the air filter is irrevelent. pull and inspect it. you could have driven through a lot of dust, or had some oil blowby trap extra dust...

All of the above, and check your injector jumper lines for leaks, and make sure your fuel cap seals properly.

Will do. I'll pull the air filter and check it out, in addition to checking tire pressure.

Last night when I was checking my primary filter for leakiness, I had a good long look at the IP and injector lines, and it all looks like it always has to me - dry, no weeping fuel evident. None at the injectors, none on the injector return lines.

As for the fuel cap sealing, well, it feels nice and firm when I attach/detach it, but is their any more quantitative way I should consider testing how well it seals? Part of emissions testing here of course is testing that the cap seals properly, and mine was tested just last year and passed easily.

How long do you spend at each stop? You could try using an extra key to keep it running, and lock the doors. drive it hard between stops, and you may start to notice a slight increase in fuel economy over time. Not sure about how others feel about a car running at all times, but I don't think it consumes that much fuel idling (big rigs do it all the time), and it will keep it up to temp.

mention of the fuel cap got me thinking... scary I know... anyway, I have seen fuel tanks collapse from vacuum, are you getting the same amount of fuel in your tank as always?

X2 - I just replaced a weeping line last week.....I had been averaging around 22 mpg for the last 5-6 tanks......but this morning I checked and I was at 23.7mpg.

Maybe it was other factors too....but worth a shot

EDIT: sorry, I see you already checked that...

Have you pop tested your injectors and checked the timing? How many miles the engine could also just be a little tired.

Thats a little low but not that low, you should be doing 2-3 mpg better.

Haven't checked my timing or my injectors - the car has 307000 kilometres on it (so, about 191000 miles). Sure, it is very possible things are just old and a bit tired - but really, would that account for the /sudden/ change in economy? I haven't had the chance to check the injectors lately as the car is my primary driver right now, so it'd be quite awkward to have it off the road for any more than a day or two.

As for the exacts particulars of my typical driving habits - well, it's really just me driving myself and my wife to our respective workplaces and home again. The total time for each trip is about 30 minutes, but we are located downtown - so a lot of stop and go.

I'll get down to the garage later tonight and report back on the air filter and tire pressures. Let's see what the next tank brings (especially if it turns out my tires are low). This small of a change in economy certainly seems within the realm of tire pressure.