Rep Power: 0

The LT and ST fuel trim on my 1999 Honda Civic DX are consistently reading above 10 at idle, but go down a little bit when the engine is revved up. I have looked around the engine bay for vacuum leaks and have tried the brake clean spray trick but have found nothing so far. The downstream O2 sensor's heater is broken for other reasons (probably electrical), but that shouldn't affect the fuel mix right? The car also seems to be low on power, but that might just be me because i have other cars and don't drive the car all that much. Is this a serious problem, or can i just ignore it (the car is a beater).

 
Rep Power: 210

Smoke up, Johnny.
Do a smoke test on it. Seal off the throttle body, remove and blow cigar or other smoke through the brake booster vacuum line. Look all over engine to see if any smoke is leaking to pinpoint a possible leak:


Smoke up Johnny:

 
Rep Power: 0

Thanks for the advice. I did a smoke test a few days ago and again today for good measure but didn't find any leaks. I forgot to add that the exhaust manifold also has a small crack above the upstream 02 sensor. Could this be the problem?

Also, does the downstream 02 sensor heater being broken have any other effects on this issue or on the engine in general? It doesn't seem to effect the driveability as far as i;m concerned. I might start another thread about this issue though.

 
Rep Power: 210

I'm not sure but this may help: https://www.scannerdanner.com/forum/...n-or-rich.html and https://www.google.com/search?client...4dUDCAg&uact=5

Read: https://m.buyautoparts.com/blog/oxyg...-buyers-guide/ and https://www.ls1.com/forums/f6/does-p...ileage-183926/

 
Rep Power: 0

I fixed the exhaust manifold crack with high-temp JB weld and checked the fuel trims again, but there seems to be no improvement. Is this even a problem i should be worrying about, can it be attributed to normal wear in the fuel pump, injectors, fuel filter, etc. in a car as old as this one? Or is it a problem i should take a more serious look at?

 
Rep Power: 222

What kind of mileage are you getting?
How do the plugs look?

 
Rep Power: 0

i'm getting around 35 to 40 mpg combined, but it's less when i do a lot of city driving. The plugs look perfect, i've only had the car for about 2000 miles and it seems the previous owner replaced them relatively recently. (the car has around 144000 miles)

 
Rep Power: 222

That to me sounds like it's running fine

 
Rep Power: 0

It does seem to run well, but it is still adding a lot of fuel for some reason. Could it be a computer issue? Is it even a serious issue or can i just ignore it?

 
Rep Power: 222

If you're not getting black soot/smoke out of the tailpipe I wouldn't be too worried