CEL light, system too rich, hesitation, and awful gas mileage

[hondacivicduty]

Hello. Hope all is well. This is my first posting and I desperately need help. I got scammed on a 99 Civic EX that was supposed to be in great condition, but literally the day after I bought it the engine blew and had to be replaced. However, since the engine swap, the CEL light comes on and off at least once week, the efficiency is horrible (maybe 20-25 mls/gal), and it revs somewhat irregularly (goes way down to 100 rpm in neutral and sometimes cuts out altogether at stops). I went to both Honda and AutoZone to run the code: P0172. It indicated a fuel problem, specifically: MAF sensor dirty or faulty; vacuum leak; fuel pressure or delivery problem; bad O2 sensor; bad fuel pressure regulator. Upon learning this, I took it back to the mechanic who had done the engine swap. He recommended that I have the O2 sensor replaced. That was done to no avail and the light is still coming on and the fuel efficiency still godless. What on earth should I do? Is it likely to be a costly problem? What should I check or do next? I have already pumped well over $2000 into this car since I bought it less than two months ago, so the wallet is running on empty and I can't afford to do much more. Thanks in advance for any advice that you can share with me.

[hondacivicduty]

Hey! Me, again. I just wanted to clarify that this car is a 99 Civic EX and has 92K miles.

[Killa_CRX]

From the symptoms you describe, my finger is pointing towards an o2 sensor problem too... Go to autozone and get the code read again... you should have gotten back more information than just a P0172 code.

Also check and make sure one of your injectors is not stuck open, or if your spark plugs are firing properly.... does the car backfire or missfire any?

So the car has 92k miles on it... but how about the engine you had put in to replace it?

[hondacivicduty]

Hey, Killa! Thanks for your reply. Bad O2 sensor is what my mechanic said but, when I swapped it out, no change. The CEL went off for about 25 miles and then came right back on (wasn't certain if that was just due to the under hood fuse being temporarily removed or what). What next? Most importantly (since I just swapped the engine) is there any way that this indicates a bad engine? Because I only have a month warranty on the engine I bought. Is it a fuel problem only? Or potentially more, since I never had this issue before the swap.

[hondacivicduty]

What exactly is a misfire? What are the indicators of it?

[Killa_CRX]

Originally Posted by hondacivicduty

What exactly is a misfire? What are the indicators of it?

Have someone check the wiring to the primary o2 sensor to make sure there are no loose wires.

the indications of a miss fire are when the spark plus does not spark for one reason or another in any of the cylinders.

[hondacivicduty]

After all that research and run-ins with several shady shops and mechanics, finally I took my civic to a honda specialist to find out that I was dealing with to completely seperate problems. The shaking in first gear was chatter caused by a bad clutch replacement in which my craptastic mechanic neglected to properly resurface the flywheel before replacing the clutch. The inefficiency and the check engine light, however, were caused by super-tight exhaust valves that had not been adjusted when my engine had been replaced. Now the fuel efficiency and check engine light issues are totally resolved (thank God!). Unfortunately, though, I am still dealing with the crappy chatter, at least until I can afford to get my clutch redone.