Hi everyone !

I am in desperate need of a good advice from the conaisseurs.

I've got a 98 Civic LX (D16Y7 engine) back in July. Extremely well maintained and checked/serviced by the book(at Honda). To continue the history of good maintenance, in October I've realized it was the time for a new timing belt.
I went to Honda (different location) and they've done it. They recommended to replace the water pump too, and I agreed.
All went well until I drove home...
Check engine light came on for the first time. I went back to the shop and after many attempts to talk me down, they accepted to read the code.
It was P0170 and P0172.
Needless to say, they insisted it's just a pure coincidence and has nothing to do with their recent work on the car.
I've sent them to their origins and I left. I'll make sure nobody will go there for service anymore...
I eventually got the CEL reset and it didn't show up again until a couple of weeks ago. At that point I invested in an OBD2 scan tool, to be able to check the codes myself.
After 2 full days of reading tons of posts and the Service Manual, I am more confused than ever.
I'll be getting a new primary O2 sensor to replace the existing Denso, although I don't think is necessary (correct me if I am wrong).
When checking the O2 sensor I've noticed a CRACK in the exhaust manifold, exactly above the sensor. I haven't removed the cover to see the extent of the crack, but I am wondering if it has something to do with P0172 system fuel too rich ???

The readings at idle are:

Coolant 190 deg F
ST FTRM -17.9
LT FTRM -15.6
MAP 10.6
Eng RPM 749
IGN ADV 12.0
IAT 73 deg F
ABSL TPS 9.8%
O2S11 0.2-0.8 (fluctuating)
O2S12 0.855 (steady)

I've just noticed the idle not being quite a purr either, but a little shaky.

Please excuse my extra long post, but I guess more details will help an educated opinion.

Thank you in advance.

 

Is the other code P0171 (running lean) rather than P0170?

If the crack is allowing outside air to mix with exhaust gases near the O2 sensor, then you could get code P0171.

Contact Honda to find out whether your Civic is covered under the Emissions Warranty, which pertains to some Civics up to 150K miles or 15 years.

 

Hi RonJ and thanks for the reply, but the codes are clearly P0170 (fuel trim malfunction-bank1)and P0172 (system fuel too rich-bank 1).

 

I was not able to find code P0170 in the 96-98 Civic service manual. Perhaps it's a generic scan tool code redundant with P0172?

 

The same codes were read by the Honda technician, back in October and I know is not in the manual..

I think P0170 (fuel trim malfunction) is just a pending code, sort of pre-code, until the computer gathers more info to pronounce the actual fault code, which is P0172 - fuel system too rich on bank 1 (in my case).

I don't know if it matters or not, but last night I clamped the vacuum hose on the fuel pressure regulator while running at idle, just to see if it makes a difference. It made no difference !!! I have a feeling the regulator might be stuck open, but I don't have the gauge to check the fuel pressure.

What do you think?

 

Any other ideas or suggestions ?

 

I ended replacing the spark plugs, last night. The idle is back to the normal PURR without being shaky, but still haven't got rid of the P0172 code...

HELP !

 

Update:

Now it's getting even more interesting. The engine stalls when I stop at traffic lights, after driving a while, so it's more than warmed-up....!
What the heck is going on ?!

The code remains consistent, unchanged at P0172 system fuel too rich on bank 1.

I need some help, 'cause I'm going nuts.

 

Again, the cracked manifold may need to be replaced.

In addition, other possible causes for P0172 are:

 

Ok I am returning after days and days of frustation...and work.

I have checked everything that the service manual indicated as a possible cause (RonJ posted the list above, as well) and after replacing the fuel pressure regulator, EVAP purge valve and O2 sensor, even PCV valve (thanks Ebay !!!), the car was doing exactly the same thing !!!

Oh well, it's good to know I have some spare parts, now.

Just before getting to dig out the injectors, I went with my gut feeling and popped out the valve cover to check the valve clearance.

Sit down and be amazed.

The morons at Honda service tighten the valves so bad, I am surprized the engine still worked !!! They were at less than half the MINIMUM clearance required by the book, on both intake and exhaust. I don't know if it was done on purpose, just to milk some more money, or they are complete retards...

Anyway, I am posting this for everybody else out there, who (perhaps) ignores the importance on valve clearance, specially on Honda engines.

Good luck everyone and feel free to ask me any questions regarding my long and intricate adventure with this type of error codes.

Cheers !