1998 Civic: code P0171: fuel pressure regulator?

Kaz Kylheku wrote in news: snipped-for-privacy@gmail.com:

Honda does not use P0170. Are you /certain/ the code you see is P0170?

What's that in civilized English?

Makes me suspect EGR, actually...

Try pinching the /return hose/, not the vacuum hose.

There is almost no difference, though I'd swear

The manual lists a whole bunch of possible causes of P0171. I'm not sure you can do this one yourself without shotgunning lots of uselessly-spent money at the car.

When did you last change your fuel filter?

I'd still get out a propane torch and make a basic test for leaks.

--scott

Never. The service table doesn't mention the fuel filter at all. Though it does seem odd that thousand and thousands of liters of fuel can pass through this little thing, and yet no change interval is published.

I've already looked up the change procedure, and how much the new filter costs from a couple of sources.

Kaz Kylheku wrote in news: snipped-for-privacy@gmail.com:

It's very unlikely the fuel filter is the cause of this problem.

Have you checked to make certain you're actually getting a P0170? If you are, there's another possible cause that's not mentioned in the manual.

With the return hose pinched off using a G-clamp, the driving experience is like this. There is some slight hesitation when accelerating from a stop during warmup. Acceleration and hill climbing is somewhat poor in general. The idle is very low, but not rough.

I would say that with the FPR return hose clamped, the car drives somewhat simlarly to how it drives when the FPR is connected normally and unrestricted. The best driveability occurs with the pinched vaccuum line.

But the car is driveable not matter what we do to the regulator; the fuel pump is clearly working. It may not be a pressure problem at all.

I'm going to do the O2 sensor test described in the service manual. (Hold engine at 3000 RPM until fan comes on, then scan the output of #1 O2 sensor, which should be 0.3 to 0.6V. If it's out of that range, it should be replaced.)

There is also a test described for a stuck or leaking EVAP purge control valve.

I did some driving while monitoring the O2 sensors and fuel trim. Some interesting findings.

The #2 O2 sensor basically has binary behavior it either reads about 0.9xx volts most of the time except during DFC0 (driving in gear with foot off throttle), when it reads a low voltage of 0.0xx at 0% fuel trim.

The #1 fuel trim and O2 reading can be described as having demonstrated two personalities.

During the first fifteen minutes of the run, fuel trim was usually at 46.9%, when accelerating, driving steadily at around 50-60 km/h, and even when idling in neutral at stops. The O2 sensor was reading about 0.485 to 0.505 volts all the time, except when coasting to a stop (DFCO) it would drop down into the

Then while I was cruising on a stretch of highway at 90 km/h, the fuel trim value adjusted down to 35%. The #1 O2 sensor value dropped, to about 0.465. Next, after I coasted to stop at a red light, the fuel trim cut to 5.5%, and the O2 reading was only 0.2xx. Big difference from previous stops, when it was

After that, there was a bit of street driving at 50-60 km/h before arriving at my destination. Now, the fuel trim did not go above 35%, and the oxygen sensor stayed in the 0.3xx range. At each stop, the trim dropped to 5.5% and the sensor to 0.2xx.

My interpretation is that this may be a bad O2 sensor, since peak value I observed was 0.505V, even at high fuel trim. It never indicates a rich mixture. Come on, the car eats a lot of gas, and its exhaust stinks of unburned fuel. You would think the O2 would indicate rich at some point?

The observed change in behavior could be that the ECU realizes that the O2 lean indication is garbage, and cuts back the rich fuel trim.

Hmm; looks a lot like the repair bucks should be spent in the direction of a new O2 sensor. Will check for that possible exhaust manifold leak, though.

Kaz Kylheku wrote in news: snipped-for-privacy@gmail.com:

Asking for the THIRD time: Are you sure you get a P0170 code in addition to the P0171?

Yes; I think I can read the screen! Two different OBDII diagnostic programs show the same two codes. Both codes come back eventually after reset.

Kaz Kylheku wrote in news: snipped-for-privacy@gmail.com:

Honda does not use P0170.

Does your Check Engine light come on for two seconds when you first turn the key to "II", and then go off and stay off, even after the engine starts?

any "P0XXX" code is from the universal list, not a manufacturer specific list like "P1XXX". P0170 is "Fuel Trim Malfunction (Bank 1)"

it's not a honda-specific code because it's on the universal obdII list!

highly unlikely this is an issue. filter congestion symptom is starvation when you're on a hill, fully loaded, and with a strong head wind. not before.

honda filters are high capacity and are typically good for hundreds of thousands of miles.

Tegger wrote in news:Xns9DA7C0BCF4507tegger@

Just to clarify why I've asked this: spurious codes usually mean the ECM is going bad.

I suggest you pull the ECM, remove its cover, and check for moisture or corrosion inside the ECM case. Your ECM should be behind the passenger-side kick panel, under the dashboard, just ahead of the door.

those trim percentages seem crazy high. normally, "trim" means deviation in the average from stoichiometric, and that should be just a few percentage points.

i'd two two things at this point:

1. because of the age of the vehicle, i'd go to
   formatting link
   and get a new oem sensor - ngk or denso, not bosch on a honda.
2. i'd double check on the potential vacuum leak scenario. as scott dorsey says, use a propane source to diagnose.

better yet, just google for this being a real honda code:

accord, civic, prelude.

the two common responses:

1. replace O? sensor.

1. adjust valves.

#1 being the most likely imo.

I put in my vehicle info, and that site didn't come up with any NTK/NGK sensors, just Walker, Denso and Delphi. Hmm.

That site has free shipping in the US; I'm in Canada. They will undoubtedly slap on at least 15 bucks for shipping here, if they even ship here at all. Plus, by the time the item arrives, I will waste at least another $20 in excess fuel consumpion! On a tank, it goes less than 400 km, whereas it should be closer to 600.

Better idea: yesterday afternoon I went to Vancouver Auto Parts and got a made-in-Japan NTK sensor for $78 + tax, and installed it right away. Now it drives better, and the smell of unburned fuel in the exhaust is gone. Haven't seen any rough idling or power dropout.

I will wait for the MIL to go off after a few drives. If not I will reset the codes and see whether they reappear.

Honda DOES use P0170. It is the "Temporary DTC" for both P0171 and P0172. This according to the FSM for the '00 Acura TL.

ok, good.

you should just reset them. if they re-appear, that's when you go to the next stage in diagnosis.

"E. Meyer" wrote in news:C852426C.1CF3F% snipped-for-privacy@msn.com:

That's odd.

I have TSB 03-020. This is Honda's official OBD-II DTC list as of March 29, 2003.

The TSB specifically says: "This is a list of all DTCs for all OBD II models. No one model has all these DTCs."

P0170 is NOT listed.

Can you give some details on the "Temporary DTC" thing?