Dreadful fuel consumption

Hi all, I'm new to the forum. I've got a 2002 C4S Tip with 31k miles on the clock, FSH. Problem with the car is I can only manage some 180miles from a full tank. The car has just been serviced by the dealers (oil service) and it's got new plugs last year (also at the dealer). The driving that I do admittedly is not hwy but I'm also not stuck in traffic. From what I read on here people are managing at least twice my figure! I drive with a careful right foot and don't race the car at all. Just had the MAF cleaned today. Also, the car has a slight stutter when cold when pulling away from stationary. Could this be related? It's all well and good once warmed up... Any ideas?? Cheers, Jeff

What's your avg mpg

Around town I get about 300km's(180miles) from a full tank. On a long run at 110km/h maybe 500km's non stop but never tested to empty. Just indicated. Around town I have seen average consumption as bad as 30L/100km... well, I wouldn't say bad more like fun! I think 180miles for a tank is within my expectation. Keeping it above 3000rpm keeps the oil companies in business. :-)

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As shown on the trip computer, it is around 17-18 UKMPG, which equates to roughly 14-15 USMPG. Thing is though, the calculation is not accurate (i.e. from the calculations, the car has somehow lost say a gallon or two)... I don't know what are the usual suspects for the fuel consumption in these cars. There is a very noticeable stutter/lag when the car is cold and accelerates from a standstill... Thx mate.

well, I average about 16.8 mpg in Boston / suburban driving - I'd say your mpg isn't far off. you may be running a little rich but hard to say without you doing some diagnostics on durametric or a dealer computer hookup while running. But frankly, I don't think many of us bought this thing for the fuel economy....

My trip computer indicates around 22 mpg

Best I get is 22-24 on the highway long distance drives. Around town I get between 14-18. If i got more, I would be driving the car the way it was not supposed to be driven!

I'm currently at a 15.6 average on the computer. I've always gotten horrible mileage while my wife can get in the 21-22 range.

We don't have enough information to know if you have an issue, but I suspect not. My highway mileage was ~24-26mpg, my mixed city suburban driving was ~17-18mpg, and my all urban driving (short trips, traffic filled) were ~12-14mpg. Conditions play such a huge role in fuel consumption I don't think you can generalize without more data. At least you're doing better than me at the track (9-10mpg)

Quotes source post: 10907485

true statement

'03 C4S I bought 3 weeks ago has fairly similar number. I am getting about 18 mpg mixed highway>city. On the road up from South Carolina I got 25.7 mpg all highway.

Anything above 12mpg and you're not driving it right. 14-15 sounds on par with urban driving. What wheels you have by chance? I noticed for heavy urban driving, lighter wheels can net you 1-2mpg more as well. For example going from 32+ lb 19s to 18" forged 20lb wheels.YMMV

Quotes source post: 10907485

Hear! Hear!

Your fine...same thing with me. I do about 10 stoplights, 15 miles one way and a section of highway about 1 mile long going to work. I fill up when I have a quarter tank remaining. My best mileage so far has been 17MPG and my worse was 14.5 MPG - must have hit every light a few times on that tank. Gas mileage is good on the highway in 6th gear at 75 - but, not so good in town.....oh well. I drive a Porsche 911 (996) to work and everywhere else - everyday - life is good!! Ray

I always end up with mixed driving between city and highway. I average 22+ mpg.

Is this the Prius forum?

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Hahaha! Exactly

I don't worry about the gas mileage in the 911. That said, I certainly keep an eye on it as a possible indicator of maintenance issues. On an average tank, I get between 18-20 mpg, more on longer highway trips and much, much less on PCA barbeque runs, mountain tours, and occasional excursions to my favorite roads.

if the OP is getting 180 miles out of a full tank to empty, and you are not flogging it no stop, something is wrong. All my driving is stop and go city style and I'm never shifting before 4 grand. I get 260 miles out of a tank.

Thanks for the replies guys! Just to clarify, like you guys, I don't care much about the money for fuel, it's the fact that the car needs a refuel every other day if I take it to work! It's only just occurred to me this fuel consumption problem as I usually go to work by a E250 and it's gone in for repairs (the missus, the iPhone and a post in the car park). I am also worried that there's some problem with the car that I or the dealer didn't pick up. Just put in an order for the durametric cable

Get your alignment and suspension checked. I had horrific MPG and a floating front end at high speed when I first purchased my car, and they finally found a rear trailing arm that needed to be replaced and a 4 wheel alignment as it was out of spec. My MPG jumped from 12 to 14 on the highway to 29 to 31 now in highway driving. I get less in the city, probably around 18 to 22 mpg if I drive it gently. Also try a few bottles of Techron fuel system concentrate.

Jim, Do you get that figure from a full tank till the fuel light comes on? I just brimmed it last night before the fuel light came on, but in any event less than a quarter tank, and it did 180miles...

Thanks for the suggestion! Will get a bottle of Techron plus tomorrow and will book it in for an alignment. It does track straight and feel planted though but will get it done! As for wheels I am running stock C4S wheels ie those turbo looking ones with dealer supplied S02A tires

Differences in driving really influence fuel mileage thus fuel mileage varies from driver to driver. First are you sure the filling of the tank is right? Sometimes the nozzle shuts off early. I have found for the most consistent fill ups to turn the nozzle handle nearly upside down then let the nozzle shut off on its own. Next the slight stutter could be important. I take it the CEL is dark? Does the CEL come on when you first turn the key to the on position? The car is new to you. Do you know the previous owner used good gasoline? You might consider running a bottle or two of Techron through the tank to remove fuel system/engine deposits. Follow directions and I prefer to change the oil/filter after the last tank with Techron gets low enough to prompt me to add fuel, which is generally about a 1/4 tank of fuel remaining. Also, these engines benefit from a good run. No need to go out and behave like a rally driver on meth but a good highway jaunt of 30+ miles can have the engine perk up noticeably. 'course, before you head out you want to make sure there is nothing else that can account for the behavior and poor fuel mileage. About fuel: Be sure to use the proper grade of fuel, octane grade, and buy top tier gasoline and buy from a busy station. Supermarket station gasoline varies in quality is what an Evo (UK car mag) fuel test a few years found and even gasoline at any station can vary in quality if the fuel is old and thus stale. High octane fuels go stale quick hence the advise to buy from a busy station. Anyhow, the stutter could be an early warning of a failing AOS. My 02 Boxster exhibited a mild hesitation when moving off from a stop and this eventually proved to be due to the AOS. You will need to consult with an experienced Porsche shop to have this possibility looked into. Things you can do to help fuel economy. Be sure the engine intake air filter is not too dirty. Check the tire pressures and be sure they are set right. When cold weather hits tire pressures plummet and they need to be adjusted.

I get 28 mpg on the freeway if I try my hardest to achieve maximum mpg (easy on acceleration, careful braking, etc.). Of course, other than to see what was the best mileage I could obtain, I rarely drive like that. Even so, it averages to about 23 mpg of combined city/hwy driving, with plenty of "spirited" driving per tank full. Per the computer, I averaged 14.7 mpg on the track. I also have learned to fill it with the nozzle upside down like Macster mentions. If I don't, I can never be sure if it's completely full until it's overfilling onto the ground. The automatic shut-offs on the nozzles are a very unreliable way to know when full, but they seem to work way better when upside down for some reason that I assume is related to the shape of the bend in the fuel filler pipe.

The CEL does light up upon first turn and goes off after the car is started. I've actually got the car for quite a while, from a friend and his wife used to use it. When I cleaned the MAF today I also disconnected the battery as per research on here. Hope it does get better. Speaking of brimming it, I only get about 30-40miles out of the first quarter. Maybe I am not brimming it enough then?

You want to see bad mileage? Buy a V8 Cayenne!

^^^ Yea!

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No kiddin ...

Same again.....I only get 30-40 miles out of the first quarter tank....

A couple of thoughts: -I believe C4s have a smaller tank than C2s, at least in Mk1 vehicles. So, miles per tank is not really a good metric to determine consumption per mile. Dividing the miles driven by the number of gallons at refueling is the only way to know for sure what you're getting. -I have found that idling the engine, such as at stoplights, really affects my mileage. Heavy stop and go traffic gets me 14-15 MPG (computer indicated), while open road driving is always well over 20. Occasionally over 25 even with some fun.

Only one litre difference so should be too much variation on a tankful.

Don't know what the difference is but I get 27.3 on long runs and 24.3 around town I don't baby the car either!

The C4 and C4S utilize a "saddle" shaped gas tank that sits over the front differential. The fuel gauge only reads one side of the saddle, and it is set up to assume that the other side is full. As a result of this setup, you could be in a situation where the gauge shows that the tank is full, but it really isn't. I have this issue at certain gas stations. I also occasionally run into the issue where I can only fill the tank 3/4 of the way, and it is reflected on the gauge. Again - this only happens at certain gas stations. Have you tried filling up at different stations to see if this improves anything?

Our C4 has gotten it's float stuck a few times. I'll also get it where the pump shuts off, the gauge says it's full, then over the course of a few miles it will drop down to 3/4 full. That doesn't, however, seem to screw up the OBC calculation of the average MPG.

The C4S is not going to get great MPG because its AWD. Yours will be even worse because of the Tip auto trans. The Tip causes even more drivetrain drag and is not nearly as efficient as the 6 speed manual. Im surprised you even found a C4S with an auto as that combo seems quite rare. Im even more surprised someone actually bought one then worried about fuel mileage. Maybe post a pic of the C4S, their great cars.

My computed MPG when I last autocrossed my Corvette was 4.5...at least you know it could be worse. A speed shop with a dyno and a sniffer could tell you if your car is running rich, and it would probably be cheap since you wouldn't actually be doing any pulls. Is the car backfiring at all? If it's running way too rich, that can be a clue. My MPG was crappy in the 996 BEFORE I added the 8-degree wing shims...that pushed it from "crappy" to "horrendous." But as long as I can make it from one gas station to the next, I'm content...

19-22 mixed town & country roads. 28-30 @70-75 on highway

I think temperature had a lot to do with it. I get good economy in the winter with the exception of short journeys when it's near or below zero. Typically (all year) I get around 17 mpg around town and between 25 and 30 mpg on the motorway cruising between 80 and 90. I use premium high octane fuel only. I accelerate quickly at every opportunity it's safe outside town. When I first got the car I experimented with driving cautiously to see what mpg I could get, the conclusion was that the difference is negligible, and I seemed to get better economy around 85 than 70. Economy in stop start traffic is shocking. I would expect the higher temperatures and resulting lower air density, harder worked cooling system and probably a/c running due to your location would mean lower mpg outside winter months...

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Maybe if you drove it farther than the end of your driveway If I remember correctly the quoted numbers at the time were around 20 which was pretty good (in my opinion anyway) given what it was and as I recall the RWD numbers weren't substantially different. When it was new, out of our 4 vehicles the 996 got the best actual milage (when she was driving) as any tank that I didn't do any driving in came out at 21.5-22.5 (her V6 F150 was only 1mpg behind (again, when I didn't drive) followed by my Golf at 18 and Jag at 16).

How many gallons does it take to fill it? 16?

Cheers, all very good points. Again, the reason I'm concerned is because that might indicate a problem with the car, eg AOS as suggested by Macster. Guess it's not all that unusual after all

Forgot to mention that I came from a 986 Boxster S Tip. That did 280mi per tank easily in the same conditions...

Comparing MPGs is mostly useless IMO as there are many variables that aren't often inficated(sea level, hills, heavy urban, heavy stop n go,driving style, maintenance, avg MPH, etc)

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It reads then like you are not filling the tank completely. My 02 Boxster (and my 03 Turbo) when driven consistently through a full tank of fuel, which I can do as I use the cars the same way day in and day out or over a shorter span of time -- hours on a long non-stop drive -- gets the same miles from the 1st quarter of a tank of fuel as the 2nd, and the 3rd. The 4th I can't say for sure since I generally fill up at 3/4 level. If I continue to drive into the 4th quarter of a tank I generally adapt a more fuel efficient driving style to ensure I do not run out of fuel. I do not advocate brimming the tank. I prefer to find a fueling technique that ensures consistent and complete fueling without having to jump through hoops or fill until the gasoline appears at the top of the filler neck. This can feed raw gasoline to the charcoal canister which can ruin it. And I hate to spill gasoline. For me I have found for the Turbo turning the nozzle nearly upside down and relying upon the auto shut off work works the best. Fill ups are quite consistent. However, I know my cars well enough that once in a while -- every 25+ fill ups -- generally when I get lazy and do not turn the nozzle upside down completely the nozzle shuts off prematurely. But before trying to add more fuel, I confirm the incomplete filling by turning on the key and observing the fuel level gage needle. If this reads low then I go back and resume fueling but this time make sure the nozzle is upside down and the nozzle vapor recovery sleeve is sealing against the tank filler tube opening properly. While the Boxster is not so sensitive I have adapted the same technique for it too.

Once again. HOW MANY GALLONS OF GAS DO YOU PUT IN EACH TIME?

Getting a full load of fuel is no slam dunk. The fuel gauge at low fuel levels may not be accurate. Managing fuel requires more thinking than any other car I have owned. Back to the OP. Compared to my 911 C2 Manual coupe, your C4S, Tiptronic, cab weighs maybe 400-500 lbs more. Rough, rough numbers: 100# for wide body, 100# for 4WD, 100# for Tip, 200# for cab. That will affect your mileage. I get 19.5 mpg. When I was a new owner I got 15 mpg. The difference is I learned how to be smoother with the throttle when driving with traffic. Give me open space and I will bury the throttle.

I never get the same amount of gas ever! Have read all the fixes. The saddle tank is just that, weird & unfixable. I feel like posting "hooray" on days when I get 14 or even once got 15 gallons...now that's a good day! Always near 20 miles per gallon heavy footed or way more when relaxed driving. 180 per tank is way too low, and I think you're not filling the tank. Always upside down nozzle. I thought I had figured out the gas tank problem when twice in a row, filling 1 gallon then waiting a few minutes, and filling up the rest...it worked twice in a row...pfff. The zip tie thingy didn't work either-