My daughter's car had a sudden drop from 30 to 20mpg. I changed spark plugs, distributor cap/rotor, pcv valve and air filter is new. That got it back up to 24mpg.

The car does throws code P1457 every 400 miles or so. I can't find the evap problem but have tried multiple gas caps and never overfill the tank.

The car was throwing a code for the secondary o2 sensor on catalytic converter and I did the non-foulers trick to stop it.

I ran seafoam thru the vacuum hose off brake booster and noticed that smoke came out of catalytic converter area. Never have seen this happen.

I have driven minimally on hwy and my gut says it gets in the 30's on hwy, need to test that out.

Appreciate your input.

-william

 

check for cracks in the exhaust manifold...

also, check fuse #15

https://honda-tech.com/forums/showpo...50&postcount=1

 

Sounds like an exhaust leak near the primary O2 sensor. That will definitely kill gas mileage. When you fix the leak, adjust the ignition timing to spec and consider also replacing the spark plug wires.

P1457 can also be caused by a vacuum leak. Is the engine having any idle problems?

 

Can the catalytic converter be welded/fixed or does it have to be replaced?

Also, is the poor mileage caused by the "brain" making adjustments based on the information coming back from the primary O2 sensor?

thanks, I like to understand what is going on.

-william

 

Listen to ron he knows his **** I would replace the cat if it is craked or broken.

 

if the only problem with the cat is the crack along a seam, i would guess rewelding it would be practical.

but you gotta think, a cat as old as that one may be time to get replace anyway

 

I did two (2) 100 mile runs on the highway this week. The first one on level payment and I got 37+mpg.

The second was from Spg to Branson (big hills) and I only got 27mpg (car was downshifting to get up some of the hills).

If I'm going to replace the cat, where should I be looking to find a new one? My civic is the DX model.

-wgc

 

Try getting it welded or something to patch up the hole. I've got the same problem but mine apparently isn't as serious so I guess that' why I've been able to get away with it. One thing I would do is try to clean the electrical grounds in the engine bay as that my improve your o2 sensor's signal quality and allow it to send 'good data' to the computer faster instead. A weak electrical ground will disproportionately negatively affect an o2 sensor which is why I strongly suggest scrubbing every single eyelit, washer, bolt, bolt hole, etc. (don't scrape paint off!!!) with the first two grounds to work on are the alternator ground and the thermostat ground. Thermostat should be aluminum so if you see any little corrosion, just very lightly scrub it down with high grit sand paper (400?). After that, if you can, measure the resistance of every ground from ground point to negative battery terminal and if it's less than 0.5ohms, you should be good. Might also be a good idea to wiggle some wires around the engine bay while measuring resistance to make sure you don't have any damaged wires. (If numbers go up when wiggling wires, then you have a damaged wire)

 

Here's the photo....

Does it look like someone had done a cheap fix with some type of epoxy or something similar?

 

I thought you meant your cat?? that is not the cat, exhaust manifold? you meant? or am I wrong?

 

thats the manifold,

buy another or have a shop weld it closed

 

You guys are noobs... These cars use a 1 piece exhaust manifold/catalytic converter... If the manifold goes bad, you have to replace the catalytic converter which is why repairing this is such a good idea!

 

I'm reading that the manifold is cast iron and that makes it difficult to get a good weld.

Other option I see is getting another 'system' for an EX and adapting it to the car.

BTW, I live in MO

 

From the look of the picture, you need the whole thing.

 

I can see bolts where the manifold connects to the cat canister. Sure looks like it would come apart in 2 pieces. * you can see three in the picture.

 

I have a little 110 mig welder, so I gave it a shot. In the meantime, I'll be looking at my options for replacing it. I'll let you know if the MPG changes. I did reset the ECU after welding it.

 

Right, I forgot DX's are one in the same, just the top of it in the pic threw me off, plus I have an EX. Those are a pain the ***, and no wonder no one tunes DX's lol.

 

I know the weld looks pretty crappy, but I'm getting 35 mpg in the city again.

 

After 1 tank of good gas mileage, the next one fell flat! Down to 22 mpg. I can't see that the weld has lifted off or anything. I don't understand it at all.

 

how did you measure the mpg? I'm just curious.

 

I LOLd good post

 

Make sure the car is warming up properly. If you can get an OBD-II reader, maybe check to see if the car is properly detecting that the car has warmed up. Only other suggestion is checking the grounds with a multimeter and making sure they're less than 0.5ohms. It might be a good idea to check these ohms value on a cold engine, warm engine and on a hot engine to see if temperature influences these numbers. Probe the body of the o2 sensor and the battery negative ground and see if the ohms of the ground changes depending on temperature of the manifold.
Fill gas tank to completely full. Reset trip odometer. Drive. Fill up gas tank again to the top. Note miles you drove. miles/gallons=mpg. So if you drove 300 miles and you filled up with 9 gallons, your mpg is 33.



Edit: **** I forgot, you have a check engine code coming up with the EVAP system... Uh, maybe you should replace the vacuum hoses that go to the EVAP system since they could be old/cracked, creaking a vacuum leak (waste gas), generating CEL, and possibly causing the EVAP system to malfunction.. I can't believe nobody addressed this issue in this thread. That EVAP working could be very temperature dependent. If you get the EVAP system fixed, you'll probably fix your problem.

 

Hey Fleabag,

For a couple of days I noticed the car was not turning the starter over as quickly as it should. So, I broke out the multimeter and started checking out the grounds that you suggested. While I did this, I noticed a crack around the positive pole of the car battery. So I bought another one and when I was taking the positive clamp off the old one, the entire pole lifted out of the battery.

Now that I've changed the battery the car is back to getting mid 30's in the city again.

What do you think about that?

thanks,

-william

 

Nice! Question is, how and why did the battery crack? How old is the battery? Was the battery bulging or anything like that? Do you still have a check engine light?

 

For the exhaust manifold check out the Dorman OE replacement ones on ebay/amazon. They go for about $200 and are OE fit and quality.

http://www.amazon.com/Dorman-674-439...f=pd_rhf_p_t_1