Bad Fuel Economy - Toyota Nation Forum : Toyota Car and Truck Forums

macst19 · 01-05-2009, 10:43 PM

Excuse me if maybe my solution has already been found but I've read these forums for a while and did a search and haven't really found much of what I'm looking for. I'm also 17 and I don't know much about cars but I figured I would give this a shot. I have a 92 Corolla with about 166k miles on it, and had a fresh rebuild about 660 miles ago so the car is running greater than ever except for one problem, fuel mileage. First off, the car had a bad fuel pump whenever the car was sent for diagnostics so that was replaced. Now the car starts and runs and drives very smoothly. My only problem is the lack of fuel economy. I would get about 170 miles to the tank, roughly a little over 10mpg. The timing belt was replaced, new spark plugs, 02 sensor is fine, idle is fine, air filter and throttle body are clean, pcv valve is brand new, the little sensor plug that goes into the air box is plugged in. The wires are in order, and are in good condition. The car doesn't idle rough, and doesn't ever stall on me (at least for the 660+ miles I've had it since the rebuild) I can't think of anything else really that is causing this bad mileage other than perhaps fuel injectors? I'm thinking they might be dirty, and I have yet to check if the O Rings are leaking fuel or air. Could the fuel injectors be the culprit? I also have a bad fuel sending unit because my fuel gauge is all over the place. Any input would be appreciated. I bought a bottle of Gumout Fuel System Clean and when I go to fill up later this week, I'll check it out.

Thanks in advance,

Melvin

ae924d · 01-06-2009, 11:57 AM

well in my experience when you rebuild a motor would would buy a new set of injectors. if this is the case they could have put oversized injectors in it. i would check that, check your sending unit. if they didn't put new injectors, i doubt just dirty injectors would cause that much economy loss, but if you have $20 laying around go to wal-marts tire lube and express and they can do a gumout fuel system treatment that actually does a good job, and see if that helps any.

Donald · 01-06-2009, 05:28 PM

If your injector seals were leaking, you would smell gasoline, and or see it pooling around the injectors.

Have the compression and timing checked by someone other than the shop that did the rebuild.
A bad 0xygen sensor is also possibility.

I doubt that Injectors would be changed at a rebuild, unless they were bad. Even then, I doubt oversized injectors would be put in.

macst19 · 01-07-2009, 03:18 PM

Donald, how could I tell if the O2 sensor is bad? The check engine light does not turn on, the injectors are clean, and are not leaking. I'm just real confused as to why the car is running like this.

Donald · 01-07-2009, 05:53 PM

Quote:

Originally Posted by macst19

Donald, how could I tell if the O2 sensor is bad? The check engine light does not turn on, the injectors are clean, and are not leaking. I'm just real confused as to why the car is running like this.

If you have no check engine light, then it probably is not the O2 sensor.

Another possibility is the cold start injector switch could be bad. That might keep the cold start ingector running after the engine is warm. It is one of those temp sensors at the thermostat area. You will need the manual for your car to figure out which one it is and how to test it.

Is your tail pipe very sooty, if so this could be it.

macst19 · 01-07-2009, 09:37 PM

I'll have to pick up an voltmeter to check out the cold start injector. I know where it's at. As for soot in the tailpipe, I think it might have some in there but it could be from the old engine which burnt oil like crazy. I do remember however driving the car home from the shop, I stepped on the gas and alot of dark smoke came out the exhaust pipe. It was also dark and cold but I haven't paid much attention since then to that. I'll check that out tomorrow. Could a bad speed sensor cause this? My speedometer needle shakes at all speeds.

j2b4osan · 01-08-2009, 06:36 AM

I would check the brakes. Often on these old jap cars the calipers start to stick so the car has to over power the brakes in order to move. So it's like the car is dragging itself or somethng. If from a stop you can let off the brake and the car starts to move smoothly (without giving gas) than t this probably isn't the problem. But sticking brakes can and will kill mpg.

macst19 · 01-08-2009, 03:49 PM

Well I feel like a complete idiot. I had changed the sparkplugs with my dad a few weeks ago because the car had cheap autolite plugs and the first plug was foul. We didn't think much of it, well I didn't and my dad well he knows about cars but maybe he overlooked this. Well today I didn't drive the car to school because it didn't start. I got home, I tightened the negative terminal and bam the car started. I drove it around a little and had smoke pop out the muffler for a few seconds but then it was fine whenever I floored it. I parked the car, started checking the plugs and as soon as i pull wire 1 oil splatters out. I'm no mechanic but that's not right. I'm thinking the valve cover gasket wasn't sealed right because the other ones are fine when I checked them. Is this my culprit for such bad gas mileage? I hope you guys agree because man I'm 17, I don't know much about cars.

Donald · 01-08-2009, 06:04 PM

Quote:

Originally Posted by macst19

Could a bad speed sensor cause this? My speedometer needle shakes at all speeds.

No, I doubt that the computer doesn't use a speed sensor signal for engine control.

Quote:

Originally Posted by macst19

I parked the car, started checking the plugs and as soon as i pull wire 1 oil splatters out. I'm no mechanic but that's not right. I'm thinking the valve cover gasket wasn't sealed right because the other ones are fine when I checked them. Is this my culprit for such bad gas mileage? I hope you guys agree because man I'm 17, I don't know much about cars.

No, that won't cause it either

What j2b4osan said is worth looking into. Jack up one wheel at a time, chock one other, turn the wheel to see if it spins freely.

When you jack up the back, let the parking brake off.
When you jack up the front, put the shifter in neutral.

j2b4osan · 01-09-2009, 03:33 AM

When you say "oil splatters out do you mean 1)when you pull the plug wire above the plug was filled with oil? 2)Or do you mean when you pulled the plug oil came out of the cylinder?
I'm no rebuild expert but if the answer is 1) I would say the valve cover o-ring wasn't seated proporly or was forgotten altogether. And if the answer is 2) I'd say you got a bum rebuild and something has failed internally( like a piston ring or sleeve, stuck valve ...)
Good luck

90 GP · 01-09-2009, 03:54 AM

Check the compression and compare readings to the specs for the engine. If you find any low readings that would explain your poor fuel economy and confirm that there is a problem with your rebuild.

macst19 · 01-11-2009, 06:37 PM

What I meant was that there was oil leaking from the top of the spark plug tube and on the plug wire. It's not leaking through the gasket or anything like that. The brakes are fine, I jacked the car up a few weeks ago and checked those. Compression, I don't know how to check that but the car doesn't have any loss in power.

macst19 · 01-11-2009, 06:45 PM

Another thing, the guy at the shop had said something about hydraulic something and that the car would adjust itself? What does this mean?

Rookie_One · 01-11-2009, 06:51 PM

that guy doesnt know anything about the 4A engines!

the valves tappets doesnt ajust themselve with the oil pressure on this engine to compensate the wear

Donald · 01-11-2009, 06:54 PM

Quote:

Originally Posted by macst19

Another thing, the guy at the shop had said something about hydraulic something and that the car would adjust itself? What does this mean?

If he said hydraulic lifters, find another shop. Your engine doesn't have hydraulic lifters.

The only thing on these cars hydraulic is the brakes and the clutch.