1990 Civic - mpg drop

dex3703

New Member
5+ Year Member
Hi,

I have a 1990 Civic LX sedan with 256K miles. I had a big drop in mpg beginning earlier this year. The mileage got worse but I didn't have the money to work on the car. The check engine light went on once, but didn't store a code. I noticed the spark plugs (bosch platinum) were brown and discolored.

A month ago I had work done on the car. Along with timing belt, valve adjust, some seals replaced, etc., I had the O2 sensor replaced. The car's performance was much improved and the mpg was back to what I was used to - mid 30s. After running a tank of gas through the plug color was back to normal.

I am not sure but I think perhaps this 2nd tank of gas is not nearly as good. I have 1/4 tank left and have only put about 250 miles on the tank, whereas normally I'd have over 300.

Is there something else I shoudl check in regards to this? Obvious things have been covered. I did put in a bottle of Chevron fuel cleaner with this tank, so that may be some of it. I don't want to wreck my new O2 sensor if there is something else wrong that should be addressed.

Thanks,
Derek
Seattle
 

Mr. Jollypants

Mr. f**king Jollypants
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
15+ Year Member
Seems like your running to rich.. Try replacing your Air Filter, Fuel Filter. Did you have your injectors looked at?
 


dex3703

New Member
5+ Year Member
ok

Magic8Ball said:
Seems like your running to rich.. Try replacing your Air Filter, Fuel Filter. Did you have your injectors looked at?
Air filter clean K&N. Haven't changed the fuel filter in a long time as it never seems worth it. Mechanic said injector was fine, though not sure to trust him. What do I check?
 

red_EF9si

röckïn dä älmïghty ß16
Registered VIP
5+ Year Member
10+ Year Member
hmm.. i would have said replace the o2 sensor but since you already did that...i would say replace the fuel filter, then go find some race gas (half a tank at most) and run you car semi hard. race gas will clean out your fuel system better than any "injection cleaner" additive. Hope that helps.
 


io_303

NIFOC
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
THis is my basic list on a tune up for my friends usually it helps them. I know some of the stuff if not all have been covered in the posts above me, but its just waht i do.
Plugs - Check them for color, replace if needed
Wires - Test with multi-meter and replace if needed
Coil - Ummm dont test it, swap in a good one and see if it runs any better(does anyone know how to test a coil?)
Distributor Cap - pull it off, its 3 screws and check the contacts on the inside to see if they are burnt to hell
Rotor - With the cap off look at it and see if there is excessive scoring of the basic state of it. Then make sure the gasket is back in blace before you put the cap back on.
Fuel Filter - Change if needed(look at the miles on the car)
Injectors - Injector cleaner, but might be trying race gas soon
O2 Sensor(s) - test with multi-meter, if unsure replace, they are cheap for 4th gens =)
Air Filter - Ummmm look at it, if its dirty clean/replace it
PCV valve - pull it, shake it. If it rattles then it is good, but again it is a cheap part so it might be a good idea to replace it anyway


I know i am forgetting something, if I remember it I will edit my post
 

civic31g

Rice Racers
Registered VIP
5+ Year Member
10+ Year Member
you cant test a coil to see if its going bad. just replace it and the dist cap. also. and you will have a basic tune up.
check all ur fluids and belts too. idk if it will have anyhting to do with gas, but always a good thing to check, did it on my wifes mazda a month or so ago, found out all 3 of her belts were bad and the tranny was low on fluid.
 

io_303

NIFOC
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
civic31g said:
you cant test a coil to see if its going bad. just replace it and the dist cap. also. and you will have a basic tune up.
check all ur fluids and belts too. idk if it will have anyhting to do with gas, but always a good thing to check, did it on my wifes mazda a month or so ago, found out all 3 of her belts were bad and the tranny was low on fluid.
cap...thats what i forgot.....that and the rotor
 

red_EF9si

röckïn dä älmïghty ß16
Registered VIP
5+ Year Member
10+ Year Member
dont forget to check you catalytic converter. that thing can seriously hinder performance & gas mileage.
 

io_303

NIFOC
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
red_EF9si said:
dont forget to check you catalytic converter. that thing can seriously hinder performance & gas mileage.
o thats righ...most people have thes dont they =)
 

shoemaker617

New Member
Registered VIP
5+ Year Member
10+ Year Member
red_EF9si said:
dont forget to check you catalytic converter. that thing can seriously hinder performance & gas mileage.
Im sorry for pulling your card but I have to. The only reason a catalytic convertor is install on a vehicle is for emissions purposes what it does it converts the harmful gases[NOX, carbon monoxide, carbon dioxide] into oxgen and water. So before you send this lad up the pickle tree......dont! The last thing he wants to do is buy a 600-$700 dollar cat. that he doesnt need.
 

io_303

NIFOC
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
shoemaker617 said:
Im sorry for pulling your card but I have to. The only reason a catalytic convertor is install on a vehicle is for emissions purposes what it does it converts the harmful gases[NOX, carbon monoxide, carbon dioxide] into oxgen and water. So before you send this lad up the pickle tree......dont! The last thing he wants to do is buy a 600-$700 dollar cat. that he doesnt need.
true it is restrictive, but it can get clogged bu some of the stuff that comes with emissions like unburnt gas and oil.
 

shoemaker617

New Member
Registered VIP
5+ Year Member
10+ Year Member
io_303 said:
true it is restrictive, but it can get clogged bu some of the stuff that comes with emissions like unburnt gas and oil.
OK.......all cars burn gas to run. How could you have unburnt oil clog up a cat? :?: Maybe if do a triple oil change without draining the oil pan but other then that not possible. If the car has that much unburt gas then it most likly wont even run, or maybe a misfiring cyl'.s or something.
 

io_303

NIFOC
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
shoemaker617 said:
OK.......all cars burn gas to run. How could you have unburnt oil clog up a cat? :?: Maybe if do a triple oil change without draining the oil pan but other then that not possible. If the car has that much unburt gas then it most likly wont even run, or maybe a misfiring cyl'.s or something.
Its a 90, the engine has some miles on it, s**t happens where the cat get clogged. that much unburnt gas can be caused by a slight misfire over a long time. This can also be cloged buy bad valves, or a foweled plugs. If a plug starts going bad it dosent spark as stron and wont burn all the gas in turn cloging the cat. And why the hell would not changing the oil have anything to do with not draining the pan, your just going to blow piston rings or some other seal not giving it enough time to clog the cat before you kill the engine itself.
 

red_EF9si

röckïn dä älmïghty ß16
Registered VIP
5+ Year Member
10+ Year Member
shoemaker617 said:
Im sorry for pulling your card but I have to. The only reason a catalytic convertor is install on a vehicle is for emissions purposes what it does it converts the harmful gases[NOX, carbon monoxide, carbon dioxide] into oxgen and water. So before you send this lad up the pickle tree......dont! The last thing he wants to do is buy a 600-$700 dollar cat. that he doesnt need.
uhh. the only thing i meant by "check your catalytic converter" was so see if it was clogged...and if so replace it with a test pipe or stragight pipe. i would never suggest to anyone to spend crazy money on a new oem one. however a hi flow one wouldnt be a bad investment if passing smog is of concern.
 

Beelzebubba

SubGenius Member
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
:shock:
:shock:

Wow! looks like a melted catalytic converter substrate to me.

What causes a melted cat? A lazy or inoperative O2 sensor can cause too much fuel to be provided and the cat will have to work harder to burn the extra HCs.

Catalytic converters do fail. Especially on 15 year old cars.
 


Top