sinyce

Need some expert advise, cuz I'm stumped, here's what I've done so far:
1. New fuel pump, Bosch complete hanger
2. New fuel filter - Honda OEM
3. New fuel pressure regulator - Honda OEM
4. Fuel Pressure Guage atop the Fuel Filter
5. Fuel Pressure reads 34psi at idle with FPR connected, jumps to 44 psi with FPR disconnected, snap throttle jumps to 44 psi

At this point I am ruling out a fuel delivery issue.

6. Rebuilt throttle body, looks almost new
7. Sent out Fuel Injectors for servicing - report came back with no issues
Dont think the injectors are leaking, because I see the fuel pressure at 34, even when i shut the car off.
8. Took apart the IACV on the rebuilt TB, looks brand new no carbon, clean, I still shot it with carb cleaner and reinstalled
9. Burped / Bleed the coolant system after that, until fan came on 2x
10. Plugged every vacuum line at the intake manifold:
- Brake booster - no changes in scan tool on STFT
- PCV Valve - no changes in scan tool
- Solenoid Purge valve port -- no changes in scan tool
- Cruise Control - no changes on scan tool on STFT
11. Replaced PCV Valve and Hose -- Honda OEM ---old hose was collapsed.
12. Sprayed carb cleaner where Intake Manifold meets the head - nothing

At this point I am ruling out any issues with a major vacuum leak, past the TB BUT before the exhaust manifold.

13. Compression Test was shocking for a 210,000 Miles car at 150psi on all 4 cylinders +/- 2 psi. (150, 150,153,151)

14. Spark Plugs are NGK - Honda OEM models. Spark plug wires are within Ohms - these are the newer 10.2 mm.

16. Replaced Primary Heated Oxygen Sensor with Denso - First time fit - no splicing.

17. Car has no drivability issues, idles fine, no stumbling or hesitation. There is a slight rough idle but I've seen that on many civics - the idle stays between 750-800 rpms.

On my to do list:
18. Check the aftermarket 4-2-1 exhaust manifold for leaks - not sure how.
19. Replace the Secondary 02 sensor
20. Replace the IATSensor, although I think this good, I've seen the scan tool show air temp at 33 and climb to 46 degree Celcius, so I'm guessing that it works.
21. Smoke test - dont have the equipment, but i'll call around

Freeze Frame Data - no surprise here
ST Fuel Trim - 26%
LT Fuel Trim - 18%
Manifold Absolute Pressure: 32 kPa (not sure) but I live near the water, so sea level
Primary 02 sensor sine waves between .1 - .8 volts and averages at 4.5
I'm getting betwwen 24-27mpg, and that sucks it used to be in the 30's.

Gents please read the above carefully, before snapping off random suggestions. I've done tons of research on this subject - ScannerDanner, Schroedersbox, and Eric-the-car guy have some excellent footages on youtube on this subject. I'm still stumped.

Former User

Sounds like an exhaust leak. See any cracks in the exhaust manifold?

sinyce

Visually no, but I plan to pour some Seafoam via the tiny cruise control vacuum line tomorrow, let it sit for ten minutes and watch for smoke around the exhaust manifold.

Forgot to mention:
Adjusted valve clearances to Honda specs
Adjusted Ignition Timing to 12deg BTDC (the 2pin plug jumped)

Former User

The combination of poor gas mileage and running lean tells you to look carefully for an exhaust leak near or upstream of the primary O2 sensor.

Is your O2 sensor located in the exhaust manifold or in exhaust pipe A?

sinyce

Good question that worried me for a while, a few years ago i installed an aftermarket exhaust header, this header pipe connects to a downpipe. the 02 on the stock is located on top of the header.
On this aftermarket the 02 is located on the #4 cyl pipe at the bottom near the flange that bolts on to the downpipe.
So I'm thinking this setup only reads the gasses from my #4 cylinder. But this code only started a few months ago.
On the stock header, Honda did have a recall for cracks around the primary 02 sensor.

Former User

The most likely cause of the code is an exhaust leak. There are three general possibilities to focus on:

1) Leaking exhaust manifold gasket
2) Cracked exhaust manifold, including around the O2 sensor bung.
3) Leaking gasket between exhaust manifold and exhaust pipe A

Inspect all these items carefully from above in the engine bay and from below with the front end on jack stands. If there are no obvious issues, replace both gaskets and then go from there.