guku0701

i have a sc400 1992 with 190k miles. the previous owner has gutted both the cats and i get pretty bad gas mileage.like 10 mpg in city and 18 highway.my question is would i get better gas mileage if i put back catalytic converters?im thinking about magnaflow cats which cost around 70$.u guys think this is a good idea?

Vortes

Cats shouldnt effect gas mileage, something else is wrong if your gas mileage is that bad.

guku0701

so cats dont have anything to do with gas mileage?my mechanic said it would improve..i was planning to change my o2 sensors and is there any way you can tell if o2 sensors are bad by looking at them?when i took them out they looked pretty good(almost no carbon but i used a blow torch to heat them up) i kinda felt a difference but could be my mind.

Kaydee

actually it will...

the SC400 comes with 4 o2 sensors, 2 before and 2 after the main cats. If you hollow out the cats, the secondary sensors will think that you are running rich and will adjust. That is probably why you're having this problem now.

xspsi6

iTrader: (31)

If the ecu thinks there is a rich condition via 02 sensor feedback then it will lean out the mixture which will actually give you better fuel mileage.

jjpark712

iTrader: (1)

Lean fuel mixture does affect little bit but not dramatically.
It will not go too lean where it may hurt the engine.
Lean= higher operating temp in combustion chamber.

Long term fuel trim will go lean. Short term will run rich at times. So not that dramatic. If you are getting 10 mpg fix cat. I will start from there. Fyi (Non forced induction cars need back pressure from exhaust system to run more efficiently. Called scavenging using back pressure, helps to suck out exhaust gas from other combustion chambers)
That means, if you change the amount of back pressure by length of headers or larger pipes they all may affect it.

Either gain power to loose mpg. Or gain mpg to loose power.

Going back to bad mpg, lot of variables but fix that fuel mixture. Then drive it to see its gotten better.

If not, time to look more in depth. Cooling temp, air mass sensor,fuel pump efficiency fuel volume delivery, filters , injectors ect.
Probably I'm forgetting something but just a rough idea.
Plus, keep in mind that preventive service is a good way to keep your cars runnIng healthy.

jjpark712

iTrader: (1)

Quest. Why were you about to change o2 sensor when your car is hollow??

jjpark712

iTrader: (1)

Cat. I meant by cat. Why do you need to change o2 sensor when cat is hollow. May not see carbon much because your engine is running lean.

guku0701

so from alot of views i take it that i need to put cats back on.would magnaflow universal cats work?coz these are like 70$ each and oem stuff is like 200$..

xspsi6

iTrader: (31)

Obd 1 systems can not have that much control over air/fuel mixture as it is usually in the +/- 7% correction so the lack of cats are not your problem, Look else where such as a bad coolant temp sensor etc.

guku0701

[QUOTE=xspsi6;7301237]Obd 1 systems can not have that much control over air/fuel mixture as it is usually in the +/- 7% correction so the lack of cats are not your problem, Look else where such as a bad coolant temp sensor etc.[/QUOTE

where can i find the coolant temp sensor and how does it affect my gas mileage?sorry im a little new on this topic..

Cleet

iTrader: (5)

Secondary o2 sensors don't adjust, they are monitoring probes not regulating probes. They are simply for checking that the cats are doing their job.

xspsi6

iTrader: (31)

There is 2 coolant temp sensors 1 in the radiator and one on the engine. I am unsure of 92 model year cars exactly.

guku0701

i just changed the coolant temp sensor by the engine ignition coil..i have yet to test it..waiting for the ecu to reset

INTIMAZY

iTrader: (5)

Werd.

Downstream sensors are there strictly for the cats. Upper sensors are for tuning. Some cars even have factory widebands before the cats.