Erratic Fuel Economy - 1991 Camry Sedan - 3S-FE 5sp Manual

[iinoz]

I just purchased a cheap 1991 Camry (SV21) Manual Sedan, CSi model, 5sp manual with 3S-FE engine (car was made in Australia)
It drives very well, purchased it with 138,000km (86,000 miles) on the Odometer.

I always closely watch the fuel economy. I filled it up just after I purchased it and headed from the suburbs of Melbourne to South-West Gippsland where I live (150km away[93 miles]). I then had it serviced. On the first tank which included time when it was serviced I managed, 8.2 l/100km [28.7mpg] (or 12.2km/l), which I thought was rather poor. This was over 647km [400 miles] which included almost exclusively of long trips (normally around 60km [37 miles]return journey) and a trip to Melbourne and back. Nearly 100% country highway/freeway driving. Hardly any red lights or idling, or short trips (under 30km[19miles]!). I drive very carefully and conservatively using 5th gear at close to 100km/h [60 mph] and going to 4th for some sustained climbs on the highways around here.

After I filled the tank a second time I went on a 100km [60 miles]return trip, which included a fair few hills and had 2 kids and an adult passenger as well as a whole lot of shopping on the return journey. I filled up the tank at the end of this trip using the same pump as before and filled it to the extent that some fuel overflowed. This time I had ridiculously good fuel economy of 6.1 l/100km [38.5mpg](or 16.2km/l).

I then filled it up again and drove it to nearly empty, this was mainly a few trips in the area (typically 50km-70km return journey) and another trip to Melbourne. It should be noted that most of my driving occurs in early morning and in the evening, when it is cold. On this tankful I got 8.3 l/100km [28.3mpg](or 12km/l).

I then filled it up about half-way to Melbourne and filled it up again on my return. This time I got a respectable 6.9 l/100km [34.9mpg](or 14.5km/l) [for 268km- 166 miles]. This was driving late afternoon and early afternoon the next day (i.e. during the warmer time of day), and about 30km [19miles] of suburban driving in Melbourne.

The tank is nearly empty again and I have just passed 600km [372 miles] I don't think I will even break 9.0 l/100k [26mpg] (or 11.1 km/l). This time the 600km is made up of a series of trips in early morning and evening of around 60km [37 miles] return journey, like always at a steady and careful 100km/h [60mph] no red lights, no idling, mainly on 5th gear, shifting to 4th on some sustained climbs.

I always reverse into the driveway when I come back home, and I do notice that the exhaust smells a bit rich, normally you would expect a car's exhaust to have no perceptible odor after a long trip (30km+ [19miles+]) when it is fully warm. I talked to the local mechanic, he suggested that the Oxygen sensor might not me working and that it might be worth replacing, only to find out that that this version of the Camry, even though it was fuel injected did NOT have an oxygen sensor at all ! -> is that normal??
He also suggested that the air flow meter might be getting stuck, and suggested examining it and making sure it's flap was moving correctly.

Do other Australian Camrys SV21 (1987-1992) with 3S-FE 2.0 litre engine have an Oxygen sensor?

Can anyone suggest any other solutions, I live in the country and drive on highways with hardly any short-trips I would expect around 7 l/100km [33mpg] (14.3 km/l)CONSISTENTLY.
Is that a reasonable expectation?

I keep the tyres inflated at close to 32 psi (220 Kpa), and regular check the level of the oil and engine coolant. I don't keep the air-conditioner on (it's Winter now{in Australia}).

Any suggestions or ideas welcome.

[scarney1988]

I am not familiar with the australian market models, however maybe I can help a little.

First, I have a question: Why do you fill your fuel tank till it over flows? I am not sure of emissions standards in Australia, but this can cause costly damages to Evaporative systems. I assume you are doing this to get a consistent basis for fuel economy.

If your car does have an oxygen sensor you would easily be able to see it on your car. Open the hood to your engine compartment. The pipes coming out of the front of the engine and bending under it are exhaust pips. If you have an 02 sensor, you will see a small metal cylinder protruding from these pips with two wires coming out. That would be your best bet. Also, in America we have an emissions sticker under the hood which labels all emissions related components the car came with.

As far as your expectation of fuel economy, I do not think it is impossible. Unfortunatly, there are many factors which effect fuel economy.

-Driver habits
-Tire type, size, inflation, and alignment
-Weight of vehicle and payload
-Mechanical functionality (Properly running and tuned engine)
-Environment (head winds, tail winds, hills, traffic jams, stoplights)

I think you track several full tanks and record what each tank yeilded (i.e. 30 mpg) and then find the average of the 10 tanks to get a big picture average.

If you think it is running rich, that is deffinetly something you want to take care of. Could be a bunch of things.

Good luck

[finncamry]

I have a 1989 5sp manual sedan, no oxygen sensor or catalysator with 369,000km on the meter. Mostly short trips, 20-30km or so with 50/50 rural gravel roads/highway driving and occasional "pedal to the floor" accelerations. During the summer fuel consumption is 6.8-7.2l/100km depending on load and driving style. During the winter (-15 Celsius or colder) it's 8.0-8.5l/100km with studded tires.

Edit: I do very very little city driving which maybe partly explains low fuel consumption.

[270+Camry]

using anything that gets power from your accessory belt is going to make you burn more fuel. there will never really be a day where you burn the same amount of fuel as you did the day before.

if you want to really save gas, drive with your windows up. never break cause it makes you loose momentum and light up lights that your alternator has to recharge. dont turn on the radio because that draws more power. Only fuel up at night time or early morning, basically when the temperature is at it's coldest that way you get more gas for your money. Also only drive when it's cool out so u get a higher oxygen mix during combustion for better gas milage. pop it in neutral down as many hills as you can without getting below your base speed that you are trying to maintain. to hell with blinkers, lights, wipers. dont go above above 3000 rpms unless u need to climb something and tailgate the piss out of trucks. also dont drive with other people because driving with friends or family means you are going to waste more gas.

or just assume it's an old reliable car, not a hybrid, way better on gas than an SUV, drive reasonably without playing Fast and Furious everwhere you go, keep its maintenance in check and be happy you got a bomb-proof car that will last way past its shelf life.

[white90dx]

I assume the check-engine light is off? (and that it does turn on when the key is 'on' but the engine is off)

With no O2 sensor, the computer is just taking a best guess at the fuel requirements of the engine. If the temp sensor is off (air or water) or the air flow meter is not working perfectly, or a few other things are having problems it may cause what you are seeing.

It looks like you are averaging over 30mpg, so I would be happy with that.

My old '90 5-speed would get 28-34mpg around town with some freeway driving and 35-38mpg on highway trips.

Oh, and its best to stop pumping gas after the first time it automatically stops. Don't try to top it off (no need to risk damaging the paint or emissions systems for that that extra fraction of a gallon/liter)

-Charlie

PS. Thanks for doing the L/km to mpg math.

[iinoz]

thanks for all your replies, much appreciated.
- I will only fill it up up to the 1st click and leave it at that

to FinCamry: That's the sort of fuel economy I would hope for: 6.8-7.2l/100km [32-38mpg] . The Winters here in Southern Australia are pretty mild, overnight low between 0C-10C with about 5-10 days a year with morning frosts.

to 270+Camry: I would think that the type of roads and the way I drive is very gentle on the car and should produce ideal mileage figures. My driving consists of going to other towns in the area, which are around 25km-60kms away, rural highways, no red lights, all with a speed limit of 100km/h (60mph), with gentle rolling hills and flat sections, with occasional trips to Melbourne (nearly 160km/100 miles each way). I hardly go over 3000rpm.

to white90dx: I haven't had the engine light come on. So far for 2380km (1479 miles) the car has achieved only 8.1 l/100km or just under 29mpg. As I mentioned in the paragraph above to 270+Camry, this was for ideal driving conditions on quiet rural highways. I live in a small town, and walk to shops and we live across the road from the school, so no short trips to ferry kids around or to do simple errands. I only use the car when I am going out of town.

As I mentioned in the original post I think the car is running rich. Should the exhaust with a simple sniff test have any noticeable smell after a long drive (20 miles +) when idling in open air??
I was using google and others mentioned the possibility of the cold start injector is leaking or if the cold start timer switch is malfunctioning - does that make any sense to anyone?

[270+Camry]

do you have a regular place you fuel up at? reason im asking is because here where I live there are certain stations that I stay away from due to the fact that their gas flat out sucks. im thinking that you tried 3 full tanks and im guessing they weren't from the same place. i think scarney had a good point when he said to try to find an average with 10 tanks, gives you more of an average and also works out the inconsistencies between different gas stations. if you are thinking about treating your injectors that is not a bad idea either, just don't make a habit of it if you treat via gas tank, that stuff has the tendency to eat away at the liner of your gas tank.

[iinoz]

I have filled up twice at 2 different Caltex service stations with "Vortex" 98 Octane and the other times at BP (in my town) with their 98 Octane petrol/gasoline "Ultimate" -> from the same pump, which gave 2 very different mileage readings, back-to-back.

When I purchased the car it had done only 138,000km (85,700 miles) in 18 years, and it probably was mainly short trips in the suburbs, I used these fuels as I believe they have various detergents that may help to clean up various deposits that have accumulated.

I filled up yesterday with regular unleaded 91 octane from the local BP, I will see if that makes any difference.

No fuels I have used contained ethanol.

[white90dx]

Oddly enough, using fuel that is too high of a grade for the motor can decrease performance. The 3s-fe does not have a knock sensor to adjust timing to take advantage of the extra octane.

Make sure that the check-engine light does come on when the key is in the ON position but the motor is off.

Without an oxygen sensor, I don't know how you can expect to get great gas mileage. From that factory, it means they have to tune it a bit rich to be safe and account for wearing of various components since there is no feedback system in place. I always thought it was an odd place for a car manufacturer to save money...

If you have been averaging 29mpg so far on the car, that's not bad.

-Charlie

[iinoz]

I have filled up with regular unleaded the past 2 tankfuls and the car has continued to achieve poor fuel economy 8.6 l/100Km and 8.3 l/100Km (or 27.2 and 28.4 MPG). Again this was achieved with driving on 100% rural highways, as described before.

I took it to the Toyota dealer nearby, and got them to have a good look at it. They checked:

1. engine compression - OK
2. Fuel Pressure - OK
3. Throttle position sensor - OK
4. Cold start injector for leaks - none found
5. Engine temperature sensor (I assume they mean coolant temperature sensor) - OK
6. Ignition timing - OK
7. Check diagnostic fault codes - all clear
8. Checked Air Filter - OK
9. Air flow meter - Variable resistance not within Specifications

they also reported:

• spark plugs showing some wear
• Spark plug tubes need to be resealed - oil leaking into cavities
• Injectors may benefit from servicing

They quoted me a hefty A$600 (=US$520) to changeover the air flow meter (AFM) if it could not be repaired. They would send the AFM to a specialist first to see if it could be repaired, the $600 would be only if it had to be replaced.

Is this the going rate for an Air Flow Meter for an 18 year old Camry?
I will go ahead with the other recommendations as it won't cost much and the spark plug tubes will eventually give me some grief if I leave them. I just want to find out what the reasonable cost for the Air Flow Meter is before I go ahead with it.

[white90dx]

That sounds a little expensive for a new AFM... but about right for the dealer. You can probably also get a used AFM from a local junkard instead to see if it fixes the problem.

It only takes a couple bolts and clamps to get it off the car yourself. (make sure you don't unscrew the plastic connector at the top, just pop off the metal clip to pull the harness off)

-Charlie

[iinoz]

Originally Posted by iinoz

I just purchased a cheap 1991 Camry (SV21) Manual Sedan, CSi model, 5sp manual with 3S-FE engine (car was made in Australia)
It drives very well, purchased it with 138,000km (86,000 miles) on the Odometer.

...

After I filled the tank a second time I went on a 100km [60 miles]return trip, which included a fair few hills and had 2 kids and an adult passenger as well as a whole lot of shopping on the return journey. I filled up the tank at the end of this trip using the same pump as before and filled it to the extent that some fuel overflowed. This time I had ridiculously good fuel economy of 6.1 l/100km [38.5mpg](or 16.2km/l).

I then filled it up again and drove it to nearly empty, this was mainly a few trips in the area (typically 50km-70km return journey) and another trip to Melbourne. It should be noted that most of my driving occurs in early morning and in the evening, when it is cold. On this tankful I got 8.3 l/100km [28.3mpg](or 12km/l).

I then filled it up about half-way to Melbourne and filled it up again on my return. This time I got a respectable 6.9 l/100km [34.9mpg](or 14.5km/l) [for 268km- 166 miles]. This was driving late afternoon and early afternoon the next day (i.e. during the warmer time of day), and about 30km [19miles] of suburban driving in Melbourne.

Note that the 2 times I did get good fuel economy was in May for drives during the warmer part of the day, when the temperature was around 20 Celsius (close to 70 F). That was late Autumn, and the rest of my driving has been in cooler Winter weather [Southern Hemisphere - Australia]

The fuel economy became consistent, never getting above 30MPG averaging 28.6MPG over 3131miles (12.15 km/l or 8.23 l/100km over 5038km).

I mentioned to my mechanic that the temperature gauge sometimes goes quite low during a long drive, and then doesn't come back up to the normal range. He suggested replacing the radiator thermostat. It is something I didn't take note of for the first 2 months, but have been carefully observing it lately. It was replaced today, and on a 50km (return) drive to the next town, the temperature gauge sat solidly at the 12 o'clock position after the initial warm up (previously around 10-11 o'clock position). The warm up was quicker, and even with the heater on full and one long descent, the temperature gauge didn't move, whereas previously it would plummet. I assume the thermostat was previously stuck at least partially open. Another related aspect was that previously after a long journey, the car would idle higher as if the engine was not fully warm. Now it was idling at around 700rpm at the end of the drive.

I would expect that this change would improve the fuel economy, and will report back, but my wife and I now have a new car and the Camry isn't used as often, probably have one fill-up every 3-4 weeks.'

I have also mentioned this issue in a related post:Radiator doesn't like to be full