Rep Power: 0

Hey guys,
I just picked up a 99 Civic LX a few weeks ago. The engine light was on when I bought it. My code reader read bad O2 sensor (upstream) which I replaced and no more engine light.

The problem I am having is horrible gas mileage. 17 liters of fuel got me 100km which I think works out to 13MPG. I know its winter, and I live in a brutal climate (last week it was -25C to -35C) but my V8 F150 is currently getting better mileage.

I'm worried that my CAT is messed up as I have no idea how long the previous owner drove it with the engine light on. Is there any way of telling if it is screwed up or plugged? I don't want to spend a fortune to find out that nothing is wrong with the CAT. I noticed a very loud rattle at certain RPM and I'm suspecting the encapsulated upper CAT heat shield. I have removed both heat shields above and below the upper CAT. I also replaced both pressure and return gas lines, so I know its not leaking fuel.

Question 1:

Can I remove the encapsulated heat shield around the upper cat with out any problems? The only reason I ask is because the screws that hold it together are rusted so bad that I am going to have to cut it off.

Question 2:

Can I cut out the upper cat and go with headers without throwing any codes? Does it require an aftermarket tuner/computer to do this? Any comments on the 50 dollar e-bay headers?

Thanks.

 
Rep Power: 812

you need to leave the heatshields that directly cover the cat. you can remove heat shields that loosely cover over the cat and exhaust to shield the car body from the exhaust pipe (its only needed if you park in grass and a fire starts). i have all my heat shields removed and it fixed many rattles, but leave the two on that are snugly bolted to the cat. it needs heat to do its job. does your car smell bad after it warms up from the exhaust? when you listen to the exhaust, is it making puttering or irregular pulses? sounds like the car could use a big tuneup since it seems to have been neglected. usually there is an engine code thrown if the cat is bad and the sensor tells the ecu that its not working. so if the engine light is off, i would start looking at the usual tuneup items.

 
Rep Power: 189

Primary o2 sensor determines air fuel mix, replace that one first off if you are getting such horrible mileage I get roughly 440 ish kms from a tank so far and that is using my remote start to let the car warm up a few mins in the morning. Do the tune up as well, crappy spark means crap fuel mileage.

 
Rep Power: 0

In the last few weeks I changed the upper o2 sensor, fuel lines, brake lines, engine oil, fuel filter, air filter, tires, alignment and seafoamed the vacuum line. So far I've driven 230km on a full tank with 1/8th left.

 
Rep Power: 189

Well if your down to that kind of mileage its 1 of 2 things your driving habits or you are in a lot of stop and go traffic, what rpms do you shift at in the car? Mind you I also have a aem cai, apexi catback and msd ign system on my dx. Do you have a remote start in the car at all and if so how often do you use it.

 
Rep Power: 367

my mileage went down to sh%$ since i need to heat the engine for 10 minutes before leaving (5 min drive, but too cold to walk there) block heater and all
not as bad as 13 mpg, though...

 
Rep Power: 189

yeh that remote start or letting her idle in the morning really drops the old mpg on a car, my mx3 which I loved dropped from 10l/100km or 400 km/tank down to about 240ish in winter with the use of the remote start for 10 mins in the morning and that was with a block heater as well. If you want to keep her extra warm you can opt for an inline water heater which really keeps the engine warmed up for you, so much so that it can damn near keep the lower part of the windsheild defrosted.

 
Rep Power: 0

Alright, she is up to 10.5L per 100km or 22mpg. The only difference between last fill up and this fill up is temperature. I cant believe how much temperature can change fuel economy. anyone else out there experience a consecutive week of -35C (-31F) lately? coldest day was -42C with windchill. I cant remember the last time my furnace shut off..

 
Rep Power: 367

try also to look for carbon build-ups?
22 is still kind of low for a 6th gen in winter.
I am at 24 now with short drives (5 min) and an eventual 1 or 2 longer 30 min to 1 hour trips a week (just to give the car a longer drive, actually).

 
Rep Power: 189

seafom will take care of any carbon deposits except for the throttlebody and iac valve lol its deadly stuff. Check the tire pressure make sure its at 30 to 32 psi colder weather can drop regualrly inflated tires down to 25 ish or so psi on really cold days, and yes I experience as cold of not colder weather than you here in saskatchewan, it can get down to -50 with windchill no problem, today its -41 with windchill. I usually hibernate when its that cold on the weekends. 10.5l/100 km is not terrible but you should be able to squeeze a little more out of it unless you are running all season tires in which case they would freeze up on you at that temp and that makes a big difference to gas mileage as well. Intake, header and what not usually do not influence hp on these cars as much as mileage as well if you are interested, I have an aem cai and catback and I can squeeze between 8 and 9L/100 km in winter out of her if I do not use the remote start to much.

 
Rep Power: 812

usually cold weather drops alot of mpgs due to the air having more oxygen per unit volume. going from 75F to 32F i usually lose at least 10mpg on the highway. more in city. below freezing, it gets even worse. its not just the ecu dumping fuel due to having more oxygen, its the engine running on 'warmup-mode' fuel trims due to there not being enough heat to actually keep the coolant warm enough at normal operating temp. then there are the other factors like tires not rolling as easily, fluids not warm enough etc. there are so many factors that can lower mileage in the cold.

 
Rep Power: 189

yep u said it, my mx3 was terrible in winter had the 1.8L v6 in it best I ever got was 10L/200km city out of it mind you I did love that car broke my heart when it got wrote off last month after gettin nailed from behind at an intersection not far from my place. Winter that dropped to close to 13L/100 km in the city. Mine has been really good so far even when using the remote start compared to the mx3. I am really looking forward to the spring and summer months see what I get out of it.

 
Rep Power: 246

Change your plugs!!! Check voltage to coils!!! Replace wide band 02 (front one). And for me i know the new 10% ethanol gas aint helping me. 29 still but was 33 before this winter. Gets down to -10 in ny lately!!