Resolving Terrible MPG

[stanno]

Hey all;

My car recently just starting being real terrible with fuel. Petrol doesn't last very long and from time to time, i can get a hint of gas when stopped in traffic or when i park up after driving home.

so far i've checked a few systems and i've came up with these diagnosis. i wanted you guys opinions so i can know which system to tackle first or perhaps any that i've missed.

the distributor (probably the same one on it that came from factory) needs servicing i think. i had changed the o-ring recently and saw that the plastic dust proof cover was broken, and according to the manual this can cause an array of problems resulting in weak spark. and i kind of added to breaking that plastic some more when i was manhandling the dizzy. a good servicing should correct this problem i hope.

the plug wires also appear to be the ones from factory, in addition, i bought the car with one plug wire that appears thicker than the other three. however, the car was burning fuel fine before, so i doubt that it's the culprit.

the valve cover grommets appear to be done for. everytime i pull out the spark plugs, the tips (where the plug wires plug onto) are coated in oil. however, the electrodes are nice and tan. so maybe the oil is preventing them from firing properly. i tightened the valve cover nuts, cleaned the plugs and checked 'em back the next day, and they still had oil on 'em. in addition, when at idle, i can hear the engine missing, however, it doesn't miss while i'm driving (accelerating etc).

the thermostat, who knows when last that was changed, cuz i haven't changed it yet. i was reading another members thread where he was also getting terrible gas mileage and it was his thermostat. come to think of it, i think the car does take a little long to reach operating temp.

the fuel filter i did change that when i started smelling fuel fumes in the cabin whenever the car stopped in traffic. since changing it, i have noticed a significant decrease in the fumes. but from time to time, i do get a faint whiff, especially after i park up at home after coming from work.

So, what do you guys think is the most likely cause of my fuel woes.

[white90dx]

There are probably multiple things causing your problems.

First, it would be helpful to get actual numbers for your fuel economy, along with a description of your normal driving conditions (length of drive, type of roads, etc.).

Saying that 'I use up a whole tank a week!" or similar means nothing. I often go through two tanks in a day, and sometimes it takes me 12 months before I fill up the tank. (obviously, one is a road trip and the other the car is parked in my garage - but that's the point - driving conditions matter)

Oil in the spark plug tubes is normally caused by a leak around the base of the tubes. Search the forums to find how you fix it.

Replace your spark plugs, spark plug wires/cap and rotor with new factory components. If there is any damage or cracks in the main distributor body, have it replaced or fixed. Make sure there is no visible damage to the ignition coil that is located inside the distributor - replace if necessary.

If the engine temp ever moves from slightly below the middle after more than a few minutes of driving (up or down), replace the thermostat. That point on the gauge represents any engine temp from around 165*F to 205*F, so if there is any movement, something is wrong.

And lastly - FIX THAT FUEL LEAK!!! You should never be able to smell raw fuel around your car. You have a leak at the tank, filler neck, lines or in the engine bay. Find it and fix it.

-Charlie

[stanno]

i'll record some numbers the next time i add fuel. but the smell of gas definitely is coming from the engine bay, and it's not very often that i do smell it.

[stanno]

charlie;

do you think a weak/dying battery can cause weak spark?

[Mike Gerber]

After the car is warm, does your temperature gage on the dash actually move down a bit as you rev the engine? If it does, that's the sign of a thermostat that is stuck in the open position. This results in lenghty warm-up times and an engine running colder than normal. That results in increased fuel consumption, as the car is running a richer than normal fuel mixture when it is not at operating temperature. If you notice this, change out that thermostat. I prefer Toyota OEM thermostats.

Also, pay attention to what white90dx said:

"And lastly - FIX THAT FUEL LEAK!!! You should never be able to smell raw fuel around your car. You have a leak at the tank, filler neck, lines or in the engine bay. Find it and fix it."

Driving a car that is leaking fuel is extremely dangerous. Get the leak diagnosed and fixed before worrying about anything else.

Mike

[stanno]

I need help in checking for a fuel leak, cuz i can't for the life of me find any. If there was a definite leak, wouldn't i smell fuel all the time the engine is running? I don't. Ok, where would it be leaking from in the engine bay? cuz it's def not from the gas cap or tank. how often should the charcoal canister be changed? cuz mine make noises like air is escaping from it alot.

[Mike Gerber]

Originally Posted by stanno

I need help in checking for a fuel leak, cuz i can't for the life of me find any. If there was a definite leak, wouldn't i smell fuel all the time the engine is running? I don't. Ok, where would it be leaking from in the engine bay? cuz it's def not from the gas cap or tank. how often should the charcoal canister be changed? cuz mine make noises like air is escaping from it alot.

Under the hood I would look along the fuel rail and where the injectors go in to each individual cylinder. Each injector uses an o-ring. I would also check the lines going to and from the fuel filter. I would also raise the car and look at the fuel lines under the car. You obviously don't have road salt to deal with like those of us in the snow belt states, but you probably have some airbone salt to deal with in Jamaica. Salt can corrode fuel lines over time. I'm not sure on the life expectancy of the charcoal cannister. I have never had to replace one on any of my cars. Maybe someone with more experience here could chime in with an answer to that.

Mike

PS: You never answered my question in my previous post about the position of the temperature gage on the dash.

[stanno]

Sorry about that Mike, upon startup, the gauge moves from beneath the C and goes to the half point and stays there all the time the engine is in operation. The only issue i can see with it is that it takes quite a bit of driving to get it to the half point. But then again, i leave home for work at like 7am when the sun has barely just been out, so it's still relatively cool. But after work it does warm up just a bit faster.

it's interesting you mentioned the charcoal canister. I started her up this morning and i got a whiff of fuel. when i went in the bay and sniffed around and the scent was strongest when i went over the charcoal canister.

So i grabbed my manual and carried out the test according to the manual. I took the canister out and blew into the tank port. The manual states that there should be no resistance when blowing into the tank port, and also, air should flow from both the purge port and the other port beneath. i tried that test, and there was alot of resistance blowing into the tank port and no air coming out the other ports, which clearly indicated that the canister needs to be replaced. also when i blew into the tank port, there was a strong smell of gas coming from the lower port that is vented to air. I'm 99% i pin pointed where the smell of fuel is coming from.

[Mike Gerber]

Looks like you have found the problem with the gas ordor. If you don't see any visual signs of other leaks, you will probably have to replace the canister. Let us know if that solves that issue. Another way to test for a fuel leak is if you know of a tech with one of the older style wand hydrocarbon sniffers (the kind they stick in your tail pipe during polution tests). They can use the wand to probe around the car. When it get's near the gas leak the wand will go crazy.

"The only issue i can see with it is that it takes quite a bit of driving to get it to the half point."

Here in the Chicago area during the cold winter months, my cars warm up to the halfway point on the gage in about 5-7 minutes. Takes a bit longer if the temperature is under 10 degrees F. If your car is taking longer than that in your moderate climate, I would change out the thermostat, since it is cheap and easy to do. Your's may be stuck in the open position. I prefer Toyota OEM thermostats for my cars.

Mike

[stanno]

Yeah i was planing on changing it anyway, considering i have no clue when last it was changed. i'll let you know how the canister thing turns out.

[stanno]

Ok, i need some help with this.




Those poor quality pics i took with my phone you see are pics of my throttle body, which as you may can make out, is lightly coated with engine oil. This oil is coming from my pcv port on the valve cover and in addition, a small amt of oil puddles in the intake elbow.

Now from what i know, when oil vapor is burnt in an engine, it reduces octane level which in turn reduces engine power and perhaps even fuel efficiency.

my engine doesn't smoke, but that only means my oil rings are ok; right?

my engine pulls really nicely, but i don't know how it felt in tip top factory spec shape. I've heard that it's normal to see oil puddled like that as long as it's not a ton of oil, but i just have a hard time swallowing that. Can i just make a longer hose that routes those gases and oil from the valve cover to the ground and cap off the end on the throttle body, as i've seen in most performance engines locally? or is it something i should take more seriously and consider if it is a sign my compression rings are needing a change?

[stanno]

Hey Mike, going on the hunch that the thermostat was the main culprit here, early this morning i pulled the radiator cap and started the cold engine. When i took a gander inside the rad, the coolant was circulating through the engine which means that you were right about the thermostat being stuck open! This is most likely why i'm getting this terrible fuel consumption. Gonna go get a genuine one from the dealer cuz they aren't expensive Thank God..

[Mike Gerber]

^ Interesting test. I never even thought of that one.

After replacing the thermostat don't forget to bleed the cooling system properly. Let us know how long the car takes to warm up (reach operating temperature in the middle of the gage) and if it solves your poor fuel mileage issue.

Mike

[stanno]

Sure thing! What about that oil in the throttle body? Any cause for concern?

[Tatohead]

Are you sure it's motor oil? Could be general carbon buildup and sludge common in this area. I recently pulled the TB off my Camry to change the IAC and the sludge was so thick you could scoop it out of there. I cringe to think what's in the runners or intake valves.

I just replaced the thermostat on mine. Very easy on these vehicles. It WILL run better and the side benefit is that the heater will get MUCH hotter.

Good luck