1999 Corolla Running Rich - Toyota Corolla, Chevy Prizm (1998-2008)

Recently bought a 1999 Corolla CE. Love it but it is running rich. Milage is only 30 mpg and black smoke is coming from the tail pipe. Checked code. Had one code; "Engine coolant temperature always reading low." Checked coolant level and OK. Replaced thermostat and ECT and cleared code. Code is gone but milage no better. Thought about MAF sensor but it appears the '99 doesn't have one. Replaced the air filter and no better. Plugs are fine. Car is running fine and seems to have plenty of power. Any suggestions? Oh yea, it has 146K miles.

Hello and welcome to the forum. Could be other reason why you are seeing black smoke from the exhaust. The only real way to find out if it is running rich or not is to run a wideband on the car and look at the A/F mix itself. If that is not possible, at a minimum, a datalogging OBD-II scanner should be hooked up and sensor outputs to O2 sensor and fuel trims looked at. Getting 30MPG is actually pretty decent for an 8th gen - depends on if it has a 4-speed auto, 3-speed auto or 5-speed standard and the driving conditions and mix.

If the mix is truely tuned to rich - I'd double check the plug wires and plugs - if in doubt of when they were change, with that kind of mileage, I would go ahead and change them. O2 sensors could also be on their way out - a CEL doesn't have to tripped to indicate a bad O2 sensor - sometimes they get "lazy" and run that middle ground between working/not working - usually fuel economy suffers. Sometimes a bad chassi ground can have a detrimental effect on performance and fuel economy. These engines are very sensitive to electrical noise - if grounds are not 100% or if ground loops were introduced into the electrical system (aftermarket audio or poor rewiring of any electricals are good examples) - could easily cause all kinds of problems, overall fuel economy at a minimum.

Double check aire pressures - at a minimum, they should be at 30PSI - depending on driving conditions and tires on it - plumping them up a little bit can yield quite a bit more mileage.

Bikeman982

Any smoke from the exhaust (except when cold) is not a good thing.

If the car is running rich it must be due to too much fuel getting to the injectors and the air mixture not correct.

I am not sure what controls the mixture on the 8th generation cars (maybe the ECM?), but I would suspect that.

Thanks for the welcome guys. Just found out the gas I'm using has ethanol in it. Last fillup I got only 27 mpg. Has anyone done research to see what gas gives them the best milage; i.e. higher octanes, etc.? And who has the best deal with gas cards and soforth? I have to find another place to fill up. I drive around 325 miles per week just to work and back. While I'm waiting for your replies, I'll search the acrchives. Thanks again.

Most of the gas that you find will have some percentage of ethanol blended in with gasoline, usually around 10% - sometimes marketed as E10 gasoline. As most have found, runs well enough on most cars, helps reduce certain emissions, and generally ups the octane rating. Downside - less energy per unit volume - so you will tend to use more of it, than if it was 100% gas. Very few, if any gas stations, still carry virgin gasoline. Almost all are E10, standard - some support E85 (85% ethanol). NOTE: Do not run E85 in a Corolla = serious damage will occur.

As for mileage - like they say, your mileage will vary. I tend to see more MPG with higher octanes than with regular gas. Since my commute is a pretty good distance - between 80-200 miles daily, depending on site. I tend to go through some tanks pretty quickly - not much chance to skew any results. I usually average about 30-32MPG on regular in mixed driving (mostly highway). For each grade that I bump it up - I see a tangible 2MPG gain, ie. 89 octane I get 32-34MPG, 93 octane I get 34-36MPG. I attribute this behavior to normal combustion deposits that tend to shift the octane requirements upward as the miles start to roll on (have about ~150K miles on my 2002, 4-speed auto). Worse tank of gas - 87 octane Marathon, got a little more than 23 MPG. Best tank was on Shell 93 V-power - a hair under 44 MPG (this was last weekend).

I would try filling up at a couple of places and see which one does the best for you. Covering 325 miles a week - you should get a pretty good idea of which gas the car tends to run better on pretty quickly. Once that happens, then you can look into gas cards and such.

Right now - I use my American Express and Discover Cards for fillups. Both yield a 5% cash back policy on gas and auto maintenace (I've been with both for some time) - with as much gas as I use, annually about $3500 or so - nice to see $175 come back to use anyway I want. Plus, they are not station specific - I can use them anywhere. Some station specific cards might give a bigger payback initially - but most drop down too much to be worthwhile in the long term.

Thanks, fish. I'll try some different fuels. Just did the math and was surprised how much more I could afford to spend per gallon if I get even 2mpg improvement. Something over 15 cents. I never would have guessed that.

Treated the oil and gas with Seafoam and my milage is now up to 32.5 mpg. I'm getting happy now. Will still experiment with different fuels. Still looking for a card that gives cash back for gas purchases. Looked into Discover and they only give 5% back on 100 dollars worth of gas a month. I use closer to $200 worth per month. American Express Blue gives 5% back on all fuel if I spend at least $6500 per month with the card. That's not gonna happen. BP has a Visa card that gives 5% back on all fuel purchases but you have to use BP fuel. They also give 10% back the first 2 billing cycles. Chase has card that pays 3% back on any three categories that you choose. It seems BP has the best deal for me but only if I get good milage with their fuel. Will check them out and see. With 5% back it might pay to try their premium. I'll do the math with milage, 5% back, etc. and see.

P.S. Only left the Seafoam in the oil around 500 miles, then changed oil and put in Delo 400 15W40. I have an oil burning problem as well. We'll see if this slows the consumption. I was only getting about 650 miles per quart of oil before.

What is the ambient temperature like out there - running 15w40 will really put a dent in fuel economy, not to mention really tough on the valvetrain and oil pump on the 1ZZ-FE engine. That is pretty decent oil - but I would watch the oil weight, I've seen guys run 20w50, because they swear it runs better - not 6 months down the road, and the oil pump lets go. three guys running 20w50 and all three had to rebuild the engine after 20-30K on the clock. One of those guys lives close to me, the others were in Texas and Arizona - so they could technically run a little heavier oil.

For oil consumption - many have seen very good luck with running a 5w30 or 10w30 of Valvoline Maxlife High-Mileage synthetic blend motor oil. Could always try and find out where you are loosing the oil - most common in our generation of Corollas are in stuck piston rings, or leaky valve seals. Some have found good results with running a solvent like Seafoam or AutoRx to help in those cases.

Well I got a whopping 400 miles on the Delo 400 15W-40 before I had to add a quart. What is the absolute best way to get the carbon out of the piston rings if that happens to be the problem. I'll do that and then if no better I guess I'll need to consider new rings.

Signed,

Oil Poor

Well I got a whopping 400 miles on the Delo 400 15W-40 before I had to add a quart. What is the absolute best way to get the carbon out of the piston rings if that happens to be the problem. I'll do that and then if no better I guess I'll need to consider new rings.
Signed,
Oil Poor

Hi there

I have a 98 corolla and have the oil consumption issue. The very best way to get carbon out would be to get a piston job done or try a product called auto-rx. I used to go through a quart of oil every 300-400 miles but now since i have used a product called auto-rx my consumption went down i now burn a quart of oil every 1000 miles and i still have not completed the auto-rx application. Also my MPG went up i used to get 280 miles out of a tank of gas with city driving. I just recently got 310 miles out of a tank of gas. I just filled up and have driven 160 miles and still not at a half tank of gas yet i project i will get more than 310 miles out this tank of gas. I can feel the difference on the engine it is quiter and has more power has not run any better since i have owned the car. My car has 169 thousand miles and i will be doing 2 applications total of aut-rx i feel that it will defintely slow my oil consumption way down. I have since change the viscosity of oil i used also. I switched from 5w30 to 10w30 oil. Also you should change out your PVC Valve and check your valve cover gasket for leaks if you have a leak change it out also. So i would recommend this product it is bit spendy at 20+ dollars a bottle but it would be cheaper than a piston ring job or valve guide job. Good luck with the engine.

Thanks, MiToy. The Auto-rx is a little pricey. For now I am going to add 8 ounces of ATF every oil change or every four quarts of oil added and see if that will do the trick eventually. I'm also going to try the Valvoline Max-life 5W-30 that fish suggested. The heavy oil really didn't help and after doing a little research I think I know why. The 15W only comes into play at startup. Once the engine is above 80 degrees F, the oil is 40W. The 5W of the Max-life 5W-30 will make for better starting and the 30W after warm up should make for a little better gas milage, but probably won't burn much faster than the 40W, if any. I'll let you know how it works out. If it doesn't, I will try the Auto-rx.

As for the gas milage issues there is not much change. Different fuels haven't made a noticeable difference. What has made a difference is speed. If I average around 70 mph I get 32.5 mpg as compared to 30.5 if I average 75 mph and a pitiful 27 mpg if I average 80 mph. Guess who has slowed down? Still trying different things however. Thanks for the help.

a quart of ATF every 3 months or so is highly recommended. you can also add a can of the seafoam. there is a generic version available at walmart for about half the cost.

these clean the injectors and combustion chambers and add additional lubrication.

i too have noticed improved gas mileage in all the machines i use when filling with 89 octane. haven't tried 91 though.